CN114585797A

CN114585797A - Damper for mitigating vibration of downhole tool

Info

Publication number: CN114585797A
Application number: CN202080070304.9A
Authority: CN
Inventors: 安德烈亚斯·霍尔
Original assignee: Baker Hughes Holdings LLC
Current assignee: Baker Hughes Holdings LLC
Priority date: 2019-09-12
Filing date: 2020-09-02
Publication date: 2022-06-03
Also published as: SA522431934B1; BR112022004718A2; EP4028628A4; EP4028628A1; WO2021050335A1

Abstract

Systems and methods for damping torsional oscillations of a downhole system are described. The system comprises: a downhole string comprising a fracturing device; and a damping system located at least one of: in and/or on the downhole string, the damping system is configured to damp torsional oscillations of the downhole string. The method comprises the following steps: installing a damping system at least one of: on and/or in the downhole system, wherein the downhole system comprises a downhole string having a fracturing device, and the damping system is configured to damp torsional oscillations of the downhole string.

Description

Damper for mitigating vibration of downhole tool

Cross Reference to Related Applications

This application claims the benefit of U.S. patent application 16/568809 filed on 12.9.2019, which is incorporated herein by reference in its entirety.

Background

1. Field of the invention

The present invention relates generally to downhole operations and systems for damping vibrations of a downhole system during operation.

2. Description of the related Art

Boreholes are drilled deep underground for many applications such as carbon dioxide sequestration, geothermal production, and oil and gas exploration and production. In all of these applications, boreholes are drilled such that they pass through or allow access to materials (e.g., gases or fluids) contained in a formation (e.g., an enclosure) located below the surface of the earth. Different types of tools and instruments may be disposed in the borehole to perform various tasks and measurements.

In operation, downhole components may be subjected to vibrations, which may affect operating efficiency. For example, severe vibrations in drill strings and bottom hole assemblies can be caused by cutting forces at the drill bit or mass imbalances in downhole tools (such as mud motors). The effects of such vibrations may include, but are not limited to, reduced rate of penetration, reduced measurement quality, and excessive fatigue and wear of downhole components, tools, and/or equipment.

Disclosure of Invention

Systems and methods for damping oscillations (such as torsional oscillations) of a downhole system are disclosed herein. The system includes a downhole system arranged to rotate within a borehole and a damping system configured on the downhole system. The damping system includes one or more dampers mounted at or in a drill bit or other fracturing device of the downhole system. These dampers are arranged to reduce or eliminate one or more specific vibration modes and thus may enable improved downhole operation and/or efficiency.

According to some embodiments, a system for damping torsional oscillations of a downhole system is provided. The system comprises: a downhole string comprising a fracturing device; and a damping system located at least one of: in and/or on the tubular string, the damping system is configured to damp torsional oscillations of the tubular string. At least one of: on and/or in the fragmentation device, the damping system comprises at least one damper element arranged in contact with a portion of the fragmentation device.

In some such embodiments, the damper element may be disposed on or in a fracturing apparatus or drill bit attached to the downhole string.

In some embodiments, a method of damping torsional oscillations of a downhole system in a borehole is provided. The method comprises the following steps: installing a damping system at least one of: on and/or in a downhole system comprising a downhole string having a fracturing device, and the damping system is configured to damp torsional oscillations of the downhole string.

Drawings

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features and advantages of the invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings, in which like elements have like numerals, and in which:

FIG. 1 is an example of a system for performing downhole operations that may employ embodiments of the present disclosure;

FIG. 2 is an illustrative graph of a typical plot of friction or torque versus relative speed or relative rotational speed between two interacting bodies;

FIG. 3 is a hysteresis graph of friction force versus displacement for a positive relative average velocity with additional small velocity fluctuations;

FIG. 4 is a graph of friction, relative speed, and product of the two versus time for a positive relative average speed with additional small speed fluctuations;

FIG. 5 is a hysteresis graph of friction force versus displacement for zero relative average velocity with additional small velocity fluctuations;

FIG. 6 is a graph of friction, relative velocity and product of the two for a zero relative average velocity with additional small velocity fluctuations;

FIG. 7 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 8A is a graph of tangential acceleration measured at the drill bit;

FIG. 8B is a graph corresponding to FIG. 8A showing rotational speeds;

FIG. 9A is a schematic graph of a downhole system showing the mode shape of the downhole system as a function of distance from the drill bit:

FIG. 9B illustrates exemplary corresponding modal shapes of torsional vibrations that may be excited during operation of the downhole system of FIG. 9A:

FIG. 10 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 11 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 12 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 13 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 14 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 15 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 16 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 17 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 18 is a schematic view of a damping system according to an embodiment of the present disclosure;

FIG. 19 is a schematic view of a damping system according to an embodiment of the present disclosure; and

FIG. 20 is a graphical illustration of modal damping ratio versus local vibration amplitude;

FIG. 21 is a schematic view of a downhole tool having a damping system;

FIG. 22 is a cross-sectional view of the downhole tool of FIG. 21;

FIG. 23 is a schematic graphical arrangement of a drill bit having a plurality of damper elements disposed within blades of the drill bit of a downhole tool according to an embodiment of the present disclosure;

FIG. 24 is a schematic view of a drill bit having a damper element disposed about a bit shank according to one embodiment of the present disclosure;

FIG. 25 is a schematic view of a drill bit having a ring-type damper element disposed about a bit shank according to an embodiment of the present disclosure;

FIG. 26 is a schematic view of a drill bit having a ring-type damper element disposed about the bit shank and a tangential damper element mounted in the blade according to one embodiment of the present disclosure;

FIG. 27 is a schematic view of a tangential damper element according to one embodiment of the present disclosure;

FIG. 28 is a schematic view of a tangential damper element according to one embodiment of the present disclosure; and

FIG. 29 is an illustrative graph of a typical plot of force or torque versus relative velocity or relative rotational speed between two interacting bodies associated with a hydraulic damper element.

Detailed Description

FIG. 1 shows a schematic diagram of a system for performing a downhole operation. As shown, the system is a drilling system 10 that includes a drill string 20 having a drilling assembly 90 (also referred to as a Bottom Hole Assembly (BHA)) conveyed in a borehole 26 penetrating a formation 60. The drilling system 10 includes a conventional derrick 11 erected on a floor 12 supporting a rotary table 14 that is rotated at a desired rotational speed by a prime mover, such as an electric motor (not shown). The drill string 20 includes a drilling tubular 22, such as a drill pipe, that extends downwardly from the rotary table 14 into a borehole 26. A fracturing apparatus 50 (such as a drill bit attached to the end of the BHA 90) fractures the geological formation as it rotates to drill the borehole 26. The drill string 20 is coupled to surface equipment, such as a system for lifting, rotating, and/or propelling (including but not limited to) a drawworks 30 via a kelly joint 21, swivel 28, and line 29 through a sheave 23. In some embodiments, the surface equipment may include a top drive (not shown). During drilling operations, the drawworks 30 is operated to control the weight-on-bit, which affects the rate of penetration. The operation of the drawworks 30 is well known in the art and therefore will not be described in detail herein.

During drilling operations, a suitable drilling fluid 32 (also referred to as "mud") from a source or mud pit 31 is circulated under pressure through the drill string 20 by a mud pump 34. The drilling fluid 31 enters the drill string 20 via the surge arrestor 36, the fluid line 38, and the kelly joint 21. The drilling fluid 31 is discharged at the borehole bottom 51 through an opening in the fracturing apparatus 50. The drilling fluid 31 is circulated uphole through the annular space 27 between the drill string 20 and the borehole 26 and returned to the mud pit 32 via a return line 35. A sensor S1 in the fluid line 38 provides information about the fluid flow rate. A surface torque sensor S2 and a sensor S3 associated with the drill string 20 provide information about the torque and rotational speed of the drill string, respectively. Additionally, one or more sensors (not shown) associated with the line 29 are used to provide hook loading of the drill string 20 and other desired parameters related to the drilling of the borehole 26. The system may also include one or more downhole sensors 70 positioned on the drill string 20 and/or BHA 90.

In some applications, the fracturing apparatus 50 is rotated by simply rotating the drill pipe 22. However, in other applications, a drilling motor 55 (e.g., a mud motor) disposed in the drilling assembly 90 is used to rotate the fracturing apparatus 50 and/or to superimpose or supplement the rotation of the drill string 20. In either case, the rate of penetration (ROP) of the fracturing apparatus 50 into the formation 60 for a given formation and a given drilling assembly is highly dependent on the weight-on-bit and the rotational speed of the drill bit. In one aspect of the embodiment of fig. 1, the drilling motor 55 is coupled to the fracturing apparatus 50 via a drive shaft (not shown) disposed in a bearing assembly 57. As the drilling fluid 31 passes under pressure through the drilling motor 55, the drilling motor 55 rotates the fracturing apparatus 50. The bearing assembly 57 supports the radial and axial forces of the fracturing apparatus 50, the lower thrust of the drilling motor, and the reactive upward load from the applied weight-on-bit. The stabilizer 58, which is coupled to the bearing assembly 57 and/or other suitable location, acts as a centralizer for the drilling assembly 90 or portion thereof.

The surface control unit 40 receives signals from downhole sensors 70 and equipment via transducers 43, such as pressure transducers, placed in the fluid line 38, as well as signals from sensors S1, S2, S3, hook load sensors, RPM sensors, torque sensors, and any other sensors used in the system, and processes such signals according to programmed instructions provided to the surface control unit 40. The surface control unit 40 displays desired drilling parameters and other information on a display/monitor 42 that are used by an operator at the drilling rig site to control the drilling operation. The ground control unit 40 includes a computer; a memory for storing data, computer programs, models and algorithms accessible to a processor in a computer; a recorder such as a tape unit, a memory unit, or the like, for recording data; and other peripheral devices. The surface control unit 40 may also include a simulation model used by the computer to process data according to programmed instructions. The control unit is responsive to user commands entered through a suitable device, such as a keyboard. The ground control unit 40 is adapted to activate an alarm 44 in the event of certain unsafe or undesirable operating conditions.

The drilling assembly 90 also contains other sensors and equipment or tools for providing various measurements related to the earth formation surrounding the borehole and for drilling the borehole 26 along a desired path. Such equipment may include equipment for measuring formation resistivity near and/or ahead of the drill bit, gamma ray equipment for measuring formation gamma ray intensity, and equipment for determining inclination, azimuth, and position of the drill string. A formation resistivity tool 64 made according to embodiments described herein may be coupled at any suitable location, including above the lower activation sub-assembly 62, for estimating or determining formation resistivity near or ahead of the fracturing apparatus 50 or at other suitable locations. Inclinometer 74 and gamma ray equipment 76 may be suitably positioned for determining the inclination of the BHA and the formation gamma ray intensity, respectively. Any suitable inclinometer and gamma ray equipment may be used. Additionally, an azimuth device (not shown), such as a magnetometer or gyroscope device, may be utilized to determine the drill string azimuth. Such devices are known in the art and are therefore not described in detail herein. In the above-described exemplary configuration, the drilling motor 55 transmits power to the fracturing apparatus 50 via a shaft that also enables drilling fluid to be transmitted from the drilling motor 55 to the fracturing apparatus 50. In alternative embodiments of the drill string 20, the drilling motor 55 may be coupled below the resistivity measurement equipment 64 or at any other suitable location.

Still referring to FIG. 1, other Logging While Drilling (LWD) devices, generally designated herein by the numeral 77, such as devices for measuring formation porosity, permeability, density, rock properties, fluid properties, etc., may be positioned in the drilling assembly 90 at appropriate locations to provide information for evaluating the subsurface formations along the borehole 26. Such equipment may include, but is not limited to, temperature measurement tools, pressure measurement tools, borehole diameter measurement tools (e.g., calipers), acoustic tools, nuclear magnetic resonance tools, and formation testing and sampling tools.

The above described devices transmit data to a downhole telemetry system 72 which in turn transmits the received data uphole to the surface control unit 40. The downhole telemetry system 72 also receives signals and data from the surface control unit 40 and transmits such received signals and data to appropriate downhole equipment. In one aspect, a mud pulse telemetry system may be used to communicate data between the downhole sensors 70 and equipment and surface equipment during drilling operations. A transducer 43 placed in the fluid line 38 (e.g., a mud supply line) detects mud pulses in response to data transmitted by the downhole telemetry system 72. The transducer 43 generates electrical signals in response to mud pressure changes and transmits such signals to the surface control unit 40 via conductor 45. In other aspects, any other suitable telemetry system may be used for two-way data communication (e.g., downlink and uplink) between the surface and the BHA 90, including, but not limited to, acoustic telemetry systems, electromagnetic telemetry systems, optical telemetry systems, wired pipe telemetry systems, which may utilize wireless couplers or repeaters in the drill string or borehole. Wired pipe telemetry systems may be constructed by connecting drill pipe sections, where each pipe section includes a data communication link (such as a wire) extending along the pipe. The data connection between the pipe sections may be made by any suitable method including, but not limited to, a hard or optical connection, induction, capacitance, resonant coupling (such as electromagnetic resonant coupling), or directional coupling methods. In the case of coiled tubing as the drill pipe 22, the data communication link may be along the side of the coiled tubing run.

The drilling systems described so far relate to those which utilize drill pipe to convey the drilling assembly 90 into the borehole 26, with the weight on bit typically being controlled from the surface by controlling the operation of the drawworks. However, a number of current drilling systems, particularly those used for drilling highly deviated and horizontal boreholes, utilize coiled tubing to convey the drilling assembly downhole. In such applications, sometimes a thruster is deployed in the drill string to provide the desired force on the drill bit. Additionally, when coiled tubing is utilized, rather than rotating the tubing via a rotary table, the tubing is injected into the borehole via a suitable injector, while a downhole motor (such as drilling motor 55) rotates the fracturing apparatus 50. For offshore drilling, offshore drilling rigs or vessels are used to support drilling equipment, including a drill string.

Still referring to FIG. 1, a resistivity tool 64 may be provided that includes, for example, a plurality of antennas, including, for example,

transmitters

66a or 66b and/or

receivers

68a or 68 b. Resistivity may be a formation property of interest in making drilling decisions. Those skilled in the art will appreciate that other formation property tools may be used with or in place of the resistivity tool 64.

Liner drilling may be one configuration or operation for providing fracturing equipment and is therefore becoming increasingly attractive in the oil and gas industry because of several advantages over conventional drilling. One example of such a configuration is shown and described in commonly owned U.S. patent No. 9,004,195 entitled "Apparatus and Method for Drilling, Setting, and Cementing a Borehole During a Single pass" (applied and Method for Drilling a Borehole, Setting a line, and Cementing the Borehole dual Single Trip), which is incorporated herein by reference in its entirety. Importantly, although the rate of penetration is relatively low, the time to align the tailpipe to the target is reduced because the tailpipe is being drilled while drilling the borehole. This may be beneficial in expanded formations where the shrinkage of the borehole may hinder the installation of a liner. Furthermore, drilling in depleted and unstable formations using a liner minimizes the risk of pipe or drill string sticking due to borehole collapse.

Although FIG. 1 is shown and described with respect to a drilling operation, those skilled in the art will appreciate that similar configurations may be used to perform different downhole operations, albeit with different components. For example, wireline, wired pipe, liner drilling, reaming, coiled tubing, and/or other configurations may be used, as is known in the art. Further, production configurations may be employed for extracting material from and/or injecting material into the formation. Thus, the present disclosure is not limited to drilling operations, but may be used for any suitable or desired downhole operation or operations.

Severe vibrations in the drill string and bottom hole assembly during drilling operations may be caused by cutting forces at the drill bit or mass imbalance in the downhole tool (such as a drilling motor). Such vibrations may result in reduced drilling rates, reduced quality of measurements made by tools of the bottom hole assembly, and may result in wear, fatigue, and/or failure of downhole components. As understood by those skilled in the art, there are different vibrations, such as lateral, axial, and torsional vibrations. For example, stick/slip and high frequency torsional oscillations ("HFTO") of the entire drilling system are both types of torsional vibrations. The terms "vibration", "oscillation" and "fluctuation" are used in the same broad sense of repeated and/or periodic movement or periodic deviation of an average value, such as average position, average velocity, average acceleration, average force and/or average torque. In particular, these terms are not intended to be limited to harmonic deviations, but may include all kinds of deviations, such as, but not limited to, periodic deviations, harmonic deviations, and statistical deviations. The torsional vibration may be excited by a self-excitation mechanism that occurs due to the interaction of the drill bit or any other cutting structure (such as a reamer bit) with the formation. The main differences between stick/slip and HFTO are frequency and typical mode shape: for example, HFTO has a frequency typically higher than 50Hz, compared to stick/slip torsional vibrations which typically have a frequency lower than 1 Hz. Furthermore, the excited modal shape of stick/slip is typically the first modal shape of the entire drilling system, while the modal shape of HFTO may be high order and typically limited to a smaller portion of the drilling system and relatively high amplitude at the excitation point, which may be the drill bit or any other cutting structure (such as a reamer bit) or any contact between the drilling system and the formation (e.g., made by a stabilizer).

Due to the high frequency of vibration, HFTO corresponds to high acceleration and torque values along the BHA. Those skilled in the art will appreciate that for torsional motion, one of acceleration, force and torque is always accompanied by the other two of acceleration, force and torque. In this sense, acceleration, force, and torque are equivalent in the sense that any one of these does not occur without the other two. The loading of the high frequency vibrations may have a negative impact on the efficiency, reliability, and/or durability of the electrical and mechanical components of the BHA. Embodiments provided herein relate to providing torsional vibration damping on a downhole system to mitigate HFTO. In some embodiments of the present disclosure, torsional vibration damping may be activated if a threshold value of a measured characteristic (such as torsional vibration amplitude or frequency) is achieved within the system.

According to non-limiting embodiments provided herein, the torsional vibration damping system may be based on a friction damper. For example, according to some embodiments, friction between two components (such as two interacting bodies) in a BHA or drill string may dissipate energy and reduce the level of torsional oscillations, thereby mitigating potential damage caused by high frequency vibrations. Preferably, the energy dissipation of the friction damper is at least equal to the HFTO energy input caused by the bit-rock interaction.

The friction damper as provided herein may cause significant energy dissipation and thus mitigation of torsional vibrations. When two components or interacting bodies are in contact with each other and move relative to each other, friction forces act in opposite directions of the speed of the relative movement between the contact surfaces of these components or interacting bodies. Frictional forces cause energy dissipation.

Although described specifically with respect to a friction damper, the dampers, damper elements, and damper systems of the present disclosure are not limited to friction. That is, other principles of damping may be implemented using dampers having different configurations, as described below. For example, damping may be generated by viscous damping, frictional damping, hydraulic damping, magnetic damping (e.g., eddy current damping), piezoelectric (shunt) damping, and the like. As used herein, a damper element may be part of a damping system configured to dissipate energy due to relative movement between at least a portion of the damper element and a tubular string. That is, the relative movement of the damper element or a portion thereof enables energy (e.g., HFTO) to be dissipated, and thus may reduce vibration within or along the tubular string.

Fig. 2 is an illustrative graph 200 of a typical plot of friction or torque versus relative velocity v (e.g., or relative rotational velocity) between two interacting bodies. The two interacting bodies have contact surfaces and a force component F perpendicular to the contact surfaces joining the two interacting bodies_N. Graph 200 shows the dependence of the frictional force or torque of two interacting bodies on the frictional contact or characteristic of a speed weakening behaviour, such as a cutting behaviour. At higher relative speeds between the two interacting bodies (v > 0), the friction or torque has different values, shown by the point 202. Decreasing the relative speed will cause increased friction or torque (also referred to as speed weakening characteristics). When the relative speed is zero, the friction or torque reaches its maximum value. Maximum friction also known as stictionSticking friction or stiction.

In general, the frictional force F_RDependent on normal force, e.g. equation F_R＝μ·F_NWherein the friction coefficient is μ. Generally, the coefficient of friction μ is a function of speed. Herein, the normal force may also fluctuate corresponding to the excitation vibration in the normal direction. In the case where the relative velocity between the two interacting bodies is zero (v ═ 0), the static friction force F_SComponent of normal force F_NCorrelation, equation F_S＝μ₀·F_NWherein the coefficient of static friction is mu₀. In the case where the relative velocity between two interacting bodies is not zero (v ≠ 0), the coefficient of friction is called the coefficient of kinetic friction μ. If the relative speed is further reduced to a negative value (i.e. if the direction of relative movement of the two interacting bodies switches to the opposite direction), the friction or torque switches to the opposite direction and has a high absolute value corresponding to a step from a positive maximum to a negative minimum at point 204 in the graph 200. That is, the friction force versus speed relationship shows a shift in sign at the point where the speed changes sign and is discontinuous at point 204 in the graph 200. The speed weakening property is a well known effect between interacting bodies that are frictionally connected. The speed-weakening characteristics of the contact force or torque are considered to be potential root causes of stick/slip. The velocity weakening characteristics can also be achieved by utilizing a dispersing fluid having a higher viscosity at a lower relative velocity and a lower viscosity at a higher relative velocity. The same effect can be achieved if the dispersing fluid is forced through relatively small channels, since the flow resistance is relatively high or low at low or high relative velocities, respectively.

Referring to fig. 8A-8B, fig. 8A shows measured torsional acceleration versus time for a downhole system. In the 5 second measurement time shown in fig. 8A, fig. 8A shows an oscillating torsional acceleration with an average acceleration of about 0g, superimposed by an oscillating torsional acceleration with a relatively low amplitude between about 0s and 3s and a relatively high amplitude of at most 100g between about 3s and 5 s. FIG. 8B shows pairs in the same time period as FIG. 8AThe speed of rotation should be used. From fig. 8A, fig. 8B shows the average speed v₀(by line v in FIG. 8B₀Indicated), the average speed is relatively constant at about 190 rpm. This average velocity is superimposed by the oscillating rotational velocity variation with relatively low amplitude between about 0s and 3s and relatively high amplitude between about 3s and 5s according to the relatively low and high acceleration amplitudes in fig. 8A. It is noted that even in a time period between about 3s and 5s, where the amplitude of the rotation speed oscillation is relatively high, the oscillating rotation speed does not cause a negative value of the rotation speed.

Referring again to FIG. 2, point 202 shows the average velocity of the two interacting bodies, which corresponds to the average velocity v in FIG. 8B₀. In the schematic of FIG. 2, the data of FIG. 8B corresponds to a velocity having a mean velocity v₀The point around the velocity that oscillates at a relatively high frequency due to HTFO, this average velocity changes relatively slowly over time compared to HFTO. Thus, the point showing the data of fig. 8B moves back and forth on the positive branch of the curve in fig. 2 without or with only little reaching of the negative velocity value. The corresponding friction or torque therefore oscillates around a positive average friction or average friction torque and is usually positive or reaches a negative value only in rare cases. As discussed further below, point 202 shows a position where a positive average of relative velocity corresponds to static torque, and point 204 shows a vantage point for frictional damping. It should be noted that friction or torque between the drilling system and the borehole wall does not produce additional damping of high frequency oscillations in the system. This is because the average velocity of the relative velocity between the contacting surfaces of the interacting bodies (e.g., stabilizer and borehole wall) is not so close to zero that HFTO causes a shift in the sign of the relative velocity of the two interacting bodies. In contrast, the relative velocity between two interacting bodies has a high average value at a distance from zero that is large so that HFTO does not cause a sign shift of the relative velocity of the two interacting bodies (e.g., shown by point 202 in fig. 2).

As will be understood by those skilled in the art, the contact force or torque as shown in FIG. 2The weakened nature relative to the relative velocity results in energy being applied to the system for causing relative movement of the interacting bodies at an average velocity v₀Oscillating, the average velocity being high compared to the velocity of the oscillating movement. In this context, other examples of self-excited mechanisms (such as coupling between axial and torsional degrees of freedom) may give rise to similar characteristics.

The corresponding hysteresis is depicted in fig. 3 and the time plot of friction and speed is shown in fig. 4. FIG. 3 shows the frictional force F_r(also sometimes referred to in this context as cutting force) versus displacement relative to position, which moves at a positive average relative velocity with an additional small velocity fluctuation (causing an additional small displacement dx). Thus, fig. 4 shows the friction force (F) for a positive average relative velocity with an additional small velocity fluctuation (causing an additional small displacement dx)_r) Relative velocity of the magnetic flux

And the product of both (indicated by label 400 in fig. 4). Those skilled in the art will appreciate that the area between friction and velocity over time is equal to the dissipated energy (i.e., the area between line 400 and the zero axis), which in the case illustrated by fig. 3 and 4 is negative. That is, in the case illustrated by fig. 3 and 4, energy is transferred from friction into oscillation via frictional contact.

Referring again to FIG. 2, point 204 represents the advantageous average velocity for frictional damping of small velocity fluctuations or vibrations in addition to the average velocity. For small fluctuations in relative movement between two interacting bodies, the sign of the discontinuity at point 204 in FIG. 2 and the relative velocity of the interacting bodies also causes a sudden sign change in the friction or torque. This sign change causes hysteresis, resulting in a large amount of dissipated energy. For example, comparing fig. 5 and 6, fig. 5 and 6 have similar graphs as fig. 3 and 4, respectively, but show the case of zero average relative velocity with additional small velocity fluctuations or vibrations. Corresponding product below line 600 in fig. 6

Is equal to the energy dissipated during a period of time, and in this case is positive.

That is, in the case illustrated by fig. 5 and 6, energy is transferred from the high-frequency oscillation into the friction via the frictional contact. This effect is quite high compared to the case illustrated by fig. 3 and 4, and has the desired sign. It is also clear from a comparison of fig. 2, 5 and 6 that the energy dissipated is significantly dependent on the difference between the maximum friction and the minimum friction at v-0 (i.e., position 204 in fig. 2). The greater the difference between the maximum and minimum friction at 0, the higher the energy dissipated. Although fig. 3-4 are created by using a speed weakening characteristic, such as the characteristic shown in fig. 2, embodiments of the present disclosure are not limited to this type of characteristic. The devices and methods disclosed herein will work for any type of characteristic, provided that when the relative speed between the two interacting bodies changes their signs, the friction or torque undergoes a step with a sign change.

A friction damper according to some embodiments of the present disclosure will now be described. The friction damper is mounted on or in a drilling system (such as the drilling system 10 shown in fig. 1) and/or is part of the drilling system 10, such as part of the bottom hole assembly 90. The friction damper is part of a friction damping system having two interacting bodies, such as a first element and a second element having a frictional contact surface with the first element. The friction damping system of the present disclosure is arranged such that the average velocity of the first element is related to the rotational velocity of the drilling system in which the first element is installed. For example, the first element may have an average or rotational speed similar to or the same as the drilling system, such that small dynamic oscillations cause a sign shift or zero crossing of the relative speed between the first and second elements according to point 204 in fig. 2.

It should be noted that friction or torque between the drilling system and the borehole wall does not produce additional damping of high frequency oscillations in the system. This is because the contact surface (e.g.,stabilizer and borehole) does not have a zero average value (e.g., point 202 in fig. 2). According to embodiments described herein, the static friction between the first and second elements is set to be sufficiently high to enable the first element to accelerate the second element (during rotation) to an average velocity v of the same value as the drilling system₀. The additional high frequency oscillations thus introduce slip between the first element (e.g., damping device) and the second element (e.g., drilling system) at a positive or negative velocity according to the oscillations around the position in fig. 2 equal to or near point 204 in fig. 2. Inertial force F_ISlip occurs when a static friction force, expressed as the coefficient of static friction between two interacting bodies multiplied by the normal force, is exceeded: f_I＞μ₀·F_N. According to an embodiment of the present disclosure, the normal force F_N(e.g. caused by contact of the contact surface between two interacting bodies and surface pressure) and the coefficient of static friction mu₀Adjusted to achieve optimal energy dissipation and optimal amplitude. Furthermore, the moment of inertia (torsion), the contact and surface pressure of the contact surfaces and the arrangement of the dampers or contact surfaces with respect to the distance from the drill bit can be optimized.

For example, turning to fig. 7, a schematic diagram of a damping system 700 according to one embodiment of the present disclosure is shown. The damping system 700 is part of a downhole system 702, such as a bottom hole assembly and/or a drilling assembly. The downhole system 702 includes a drill string 704 that rotates to enable drilling operations of the downhole system 702 to form a borehole 706 within a formation 708. As discussed above, the borehole 706 is typically filled with a drilling fluid, such as drilling mud. The damping system 700 includes a first element 710 operatively coupled (e.g., fixedly connected) or an integral part of the downhole system 702 to ensure that the first element 710 rotates at an average speed that is related to (e.g., similar to or the same as) an average speed of the downhole system 702. The first member 710 is in frictional contact with the second member 712. The second component 712 is at least partially movably mounted on the downhole system 702 with the contact surface 714 between the first component 710 and the second component 712.

In terms of friction, the minimum friction withThe difference between the maximum frictional forces is positively correlated to the normal force and the static coefficient of friction. The dissipated energy increases with friction and harmonic displacement, but only dissipates energy during the sliding phase. In the viscous phase, the relative displacement between the friction interfaces and the dissipated energy is zero. The upper amplitude limit of the viscous phase increases linearly with the normal force and friction coefficient in the contact interface. The reason is that one of the contact bodies contacts the body to

A reaction force in the contact interface which can be caused by the inertia J of the one contact body in case of being accelerated

The torque M must be higher than the limit defining the viscous and slip_H＝F_Nμ_HAnd r. As used herein, F_NIs a normal force, and μ_HIs the effective coefficient of friction and r is the effective or average radius of the frictional contact area. For complex frictional contact parts of interacting bodies, sticking or slipping can occur simultaneously. Herein, the contact pressure may be optimized for optimal damping and amplitude.

A similar mechanism applies if the contact force is caused by a displacement and a spring element. Acceleration of contact area

May be attributable to excitation of the mode and depends on the corresponding mode shape, as discussed further below with respect to fig. 9B. Acceleration as far as contact interface viscosity is concerned with additional inertial mass J

It is equal to the acceleration of the excited mode and the corresponding mode shape at the additional location.

The normal and friction forces must be adjusted to ensure that the slip phase is within a suitable or acceptable amplitude range. The allowable amplitude range may be defined by an amplitude between zero and a load limit, for example given by the design specifications of the tool and the component. The limit may also be given by a percentage of the expected amplitude without a damper. The dissipated energy, which can be compared to the energy input (e.g., by forced excitation or self-excitation), is one measure to determine the efficiency of the damper. Another measure is the equivalent damping provided for the system, which is proportional to the ratio of the energy dissipated within one period of harmonic vibration in the system to the potential energy during one period of vibration. This measure is particularly effective for self-excited systems. In the case of a self-excited system, the excitation can be estimated by a negative damping coefficient and both the equivalent damping and the negative damping can be directly compared. The damping force provided by the damper is non-linear and strongly dependent on the amplitude.

As shown in fig. 20, the damping is zero in the viscous phase (left end of the graph of fig. 20), where the relative movement between the interacting bodies is zero. If, as mentioned above, the limit between the stick and slip phases is exceeded by the forces transmitted through the contact interface, relative sliding movements occur which cause energy dissipation. The damping ratio provided by the frictional damping then increases to a maximum value and then decreases to a minimum value. The amplitude that will occur depends on the excitation, which can be described by a negative damping term. Here, as depicted in fig. 20, the maximum value of damping provided must be higher than the negative damping from the self-excitation mechanism. The amplitude occurring in the so-called limit cycle can be determined by the intersection of the negative damping ratio provided by the friction damper and the equivalent damping ratio.

The curve depends on different parameters. It is advantageous to have a high normal force, but the slip phase occurs at the minimum amplitude of the system of the bottom hole assembly. In terms of inertial mass, this can be achieved by high mass or by placing the contact interface at a point of high acceleration relative to the excited mode shape. In terms of the contact interface, a high relative displacement is advantageous compared to the amplitude of the modal shape at the contact point, e.g., along the axial axis of the BHA. Therefore, an optimal arrangement of the damping device according to the high amplitude or relative amplitude is important. This may be achieved by using simulation results, as discussed below. The normal force and coefficient of friction can be used to move the curve to lower or higher amplitudes without having a large effect on the damping maximum. If more than one friction damper is implemented, this will result in a superposition of similar curves as shown in fig. 20. This is advantageous for the overall damping achieved if the normal force and the friction coefficient are adjusted to achieve a maximum of the same amplitude. Furthermore, a slightly shifted damping curve will cause the resulting curve to be wider relative to the amplitude, which may be advantageous to account for the effect that the amplitude may be shifted to the right of the maximum. In this case, the amplitude will increase to a very high value in the case of a self-excited system, as indicated by negative damping. In this case the amplitude needs to be moved to the left of the maximum again, for example by moving away from the bottom or reducing the rotational speed of the system to a lower level. The amplitude in this context is scaled approximately linearly by the average rotational speed as indicated and discussed with respect to fig. 8B.

Referring again to FIG. 7, the tubular string 704, and thus the downhole system 702, is rotated at a rotational speed

Rotation, which may be measured in Revolutions Per Minute (RPM). The second member 712 is mounted to the first member 710. The normal force F between the first element 710 and the second element 712 may be selected or adjusted by the application and use of the adjustment element 716_N. The adjustment element 716 may be adjusted, for example, via threads, actuators, piezoelectric actuators, hydraulic actuators, and/or spring elements, to apply a force having a component in a direction perpendicular to the contact surface 714 between the first element 710 and the second element 712. For example, as shown in fig. 7, the adjustment element 716 may apply a force in an axial direction of the downhole system 702 that translates into a force component F perpendicular to the contact surfaces 714 of the first and

second elements

710, 712 due to the non-zero angle between the axis of the downhole system 702 and the contact surfaces 714 of the first and

second elements

710, 712_N. In some configurations, the angle between system 712 and the inertial mass element is selected or defined to allow sliding motion and avoid self-locking.

The second element 712 has a moment of inertia J. When HFTO occurs during operation of the downhole system 702, both the downhole system 702 and the second element 712 are accelerated according to the modal shape (e.g., defining an amplitude distribution along the dimensions of the drilling system, drill string, and/or BHA) and the amplitude of the modal (e.g., scaling the amplitude of the modal shape). Exemplary results of such an operation are shown in fig. 8A and 8B. Fig. 8A is a graph of tangential acceleration measured at the drill bit, and fig. 8B is the corresponding rotational speed.

Due to the tangential acceleration and inertia of the second element 712, relative inertial forces occur between the second element 712 and the first element 710. If these inertial forces exceed the threshold between stick and slip, i.e. if these inertial forces exceed the static friction between the first 710 and second 710 elements, relative motion will occur between the

elements

710, 712 causing energy dissipation. In such an arrangement, the acceleration, static and/or dynamic coefficient of friction and the normal force determine the amount of energy dissipated. For example, the moment of inertia J of the second element 712 determines the relative force that must be transferred between the first element 710 and the second element 712. The high acceleration and moment of inertia increases the tendency to slip at the contact surface 714, thus resulting in higher energy dissipation and equivalent damping ratio provided by the damper.

Energy dissipation due to frictional movement between the first element 710 and the second element 712 will generate heat and wear on the first element 710 and/or the second element 712. To keep wear below an acceptable level, a material that can withstand wear may be used for first element 710 and/or second element 712. For example, a diamond or polycrystalline diamond compact may be used for at least a portion of first element 710 and/or second element 712. Alternatively or in addition, the coating may help reduce wear due to friction between the first and

second elements

710, 712. The heat may cause high temperatures and may affect the reliability or durability of the first element 710, the second element 712, and/or other components of the downhole system 702. The first element 710 and/or the second element 712 may be made of and/or may be in contact with a material having a high thermal conductivity or a high thermal capacity.

Such materials having high thermal conductivity include, but are not limited to, metals or metal-containing compounds such as copper, silver, gold, aluminum, molybdenum, tungsten, or thermal greases, oils, epoxies, silicones, polyurethanes, and acrylates, and optionally fillers such as diamond, metals or metal-containing chemical compounds (e.g., silver, aluminum in aluminum nitride, boron in boron nitride, zinc in zinc oxide), or silicon-containing chemical compounds (e.g., silicon carbide). Additionally or alternatively, one or both of the first and

second elements

710, 712 may be in contact with a fluid (such as a drilling fluid) configured to remove heat from the first and/or

second elements

710, 712 in order to cool the

respective elements

710, 712. Furthermore, amplitude limiting elements (not shown) such as keys, grooves or spring elements may be used and configured to limit the energy dissipation to acceptable limits, thereby reducing wear.

When the damping system 700 is arranged, high normal forces and/or static or dynamic coefficients of friction will prevent relative sliding motion between the first element 710 and the second element 712, and in such cases, no energy is dissipated. In contrast, low normal forces and/or static or dynamic coefficients of friction may result in low friction, and slip will occur but the dissipated energy is low. Additionally, a low normal force and/or static or dynamic coefficient of friction may cause the friction at the outer surface of the second element 712 (e.g., between the second element 712 and the formation 708) to be higher than the friction between the first element 710 and the second element 712, causing the relative velocity between the first element 710 and the second element 712 to be not equal to or near zero but to be within the range of average velocities between the downhole system 702 and the formation 708. Thus, the normal force and the static or dynamic friction coefficient as well as the arrangement of the damper element with respect to the excited mode shape and mode shape may be adjusted (e.g., by using adjustment element 716) to achieve an optimized value of energy dissipation.

This can be done by adjusting the normal force F_NCoefficient of static friction mu₀The dynamic friction coefficient mu, the arrangement of the damper element with respect to the excited mode shape, or a combination thereof. The normal force F can be adjusted in the following manner_N: positioning the adjustment element 716 and/or causing the actuator to produce a force on one of the first and second elements having a force on the first and second elementsThe force of the perpendicular component of the contact surface of the second member adjusts the pressure conditions around the first member and the second member, or increases or decreases the area on which the pressure acts. For example, by increasing the external pressure (such as mud pressure) acting on the second element, the normal force F will also be increased_N. Adjusting the pressure of the mud downhole may be accomplished by adjusting mud pumps on the surface (e.g., mud pumps 34 shown in fig. 1) or other equipment affecting the mud pressure on the surface or downhole (such as bypasses, valves, surge arrestors). The normal force may be adjusted to be a harmonic of the same frequency as the natural frequency of the excited modal shape, and thus have a low normal force value for low accelerations of the inertial mass and a high normal force value for low accelerations of the inertial mass, and thus allow a sliding motion of low acceleration values.

The normal force F may also be adjusted by a biasing element (not shown), such as a spring element_NThe biasing element exerts a force on the second element 712, for example in an axial direction away from or towards the first element 710. Normal force F may also be applied in a controlled manner based on input received from the sensors_NAnd (4) adjusting. For example, suitable sensors (not shown) may provide one or more parameter values to a controller (not shown) that are related to the relative movement of the first and

second elements

710, 712 or the temperature of one or both of the first and

second elements

710, 712. Based on these parameter values, the controller may provide an increase or decrease in the normal force F_NThe instruction of (1). For example, if the temperature of one or both of the first element 710 and the second element 712 exceeds a threshold temperature, the controller may provide a decreasing normal force F_NTo prevent damage to one or both of the first element 710 and the second element 712 due to high temperatures. Similarly, for example, if the distance, velocity, or acceleration of the second element 712 relative to the first element 710 exceeds a threshold, the controller may provide for increasing or decreasing the normal force F_NTo ensure optimal energy dissipation. By monitoring the parameter values, the normal force F can be controlled_NTo achieve the desired result within a time period. For example, the normal force F can be controlled_NTo provide optimum energy dissipation while drillingMaintaining the temperature of one or both of the first element 710 and the second element 712 below a threshold value for the stroke or a portion thereof.

In addition, the static or dynamic coefficient of friction may be adjusted by utilizing different materials, such as, but not limited to, materials having different stiffness, different roughness, and/or different lubricity. For example, surfaces with higher roughness typically increase the coefficient of friction. Thus, the coefficient of friction may be adjusted by selecting a material having an appropriate coefficient of friction for at least one of the first and second elements or a portion of at least one of the first and second elements. The material of the first and/or second element may also have an effect on the wear of the first and second element. In order to keep the wear of the first and second elements low, it is advantageous to choose a material that can withstand the friction occurring between the first and second elements. The inertia, coefficient of friction, and expected acceleration amplitude (e.g., as a function of mode shape and eigenfrequency) of the second element 712 are parameters that determine the dissipated energy and also need to be optimized. The critical mode shape and acceleration amplitude may be determined by measurement or calculation, or based on other known methods as understood by those skilled in the art. Examples are finite element analysis or a transfer matrix method or a finite difference method and analyze or analyze the modality based on the modality. It is optimal to arrange the friction damper where high relative displacements or accelerations are expected.

Turning now to fig. 9A and 9B, an example of a downhole system 900 and corresponding modality is shown. Fig. 9A is a schematic graph of a downhole system showing the mode shape of the downhole system as a function of distance from the drill bit, and fig. 9B shows an exemplary corresponding torsional oscillation mode shape that may be excited during operation of the downhole system of fig. 9A. Fig. 9A and 9B are schematic diagrams illustrating potential locations and arrangements of one or more elements of a damping system on a downhole system 900.

As schematically shown in fig. 9A, the downhole system 900 includes various components having different diameters (as well as different masses, densities, configurations, etc.), and thus during rotation of the downhole system 900, the different components may cause various modes to be generated. The exemplary mode indicates where the highest amplitude will be present, which may require damping to occur by applying a damping system. For example, as shown in fig. 9B, a modal shape 902 of a first torsional oscillation, a modal shape 904 of a second torsional oscillation, and a modal shape 906 of a third torsional oscillation of the downhole system 900 are shown. Based on knowledge of the mode shapes 902, 904, 906, the position of the first element of the damping system can be optimized. Damping may be required and/or achieved where the amplitude of the mode shapes 902, 904, 906 is at a maximum (peak). Thus, two potential locations for attaching or installing the damping system of the present disclosure are illustratively shown.

For example, the first damping location 908 is proximate to the drill bit of the downhole system 900 and primarily dampens the first and third torsional oscillations (corresponding to the modal shapes 902, 906) and provides some damping for the second torsional oscillation (corresponding to the modal shape 904). That is, the first damping position 908 is approximately at the peak of the third torsional oscillation (corresponding to mode shape 906), near the peak of the first torsional oscillation mode shape 902, and at about half the peak relative to the second torsional oscillation mode shape 904.

The second damping position 910 is arranged to provide again primarily damping of the third torsional oscillation mode shape 906 and some damping for the first torsional oscillation mode shape 902. However, in the second damping position 910, damping of the second torsional oscillation mode shape 904 does not occur because the second torsional oscillation mode shape 904 approaches zero at the second damping position 910.

Although only two positions for arranging the damping system of the present disclosure are shown in fig. 9A and 9B, embodiments are not so limited. For example, any number and any arrangement of damping systems may be installed along the downhole system to provide torsional vibration damping to the downhole system. An example of a preferred mounting location for the damper is where one or more of the modal shapes are expected to exhibit high amplitudes.

Due to the high amplitude at the drill bit, for example, one good location for the damper is close to or even within the drill bit. Further, the first and second elements are not limited to a single body, but may take any number of various configurations to achieve the desired damping. That is, multiple body (multi-body) first or second elements (e.g., friction damping devices) may be employed, where each body has the same or different normal forces, coefficients of friction, and moments of inertia. For example, such a multi-body element arrangement may be used if it is not certain which mode shape and corresponding acceleration are expected at a given location along the downhole system.

For example, two or more element bodies may be used that can achieve different relative sliding movements between each other to dissipate energy. The multiple bodies of the first element may be selected and assembled using different static or dynamic coefficients of friction, angles between contacting surfaces, and/or may have other mechanisms that affect the amount of friction and/or the transition between stick and slip. Such a configuration may be used to damp several amplitude levels, excited modal shapes, and/or natural frequencies.

For example, turning to fig. 10, a schematic diagram of a damping system 1000 according to one embodiment of the present disclosure is shown. The damping system 1000 may operate in a similar manner as shown and described above with respect to fig. 7. Damping system 1000 includes a first element 1010 and a second element 1012. However, in this embodiment, the second element 1012 mounted to the first element 1010 of the downhole system 1002 is formed from a first body 1018 and a second body 1020. The first body 1018 has a first contact surface 1022 between the first body 1018 and the first member 1010, and the second body 1020 has a second contact surface 1024 between the second body 1020 and the first member 1010. As shown, the first body 1018 is separated from the second body 1020 by a gap 1026. The gap 1026 is provided to prevent interaction between the first body 1018 and the second body 1020 such that they may operate (e.g., move) independently of one another or do not directly interact with one another. In this embodiment, the first body 1018 has a first static coefficient of friction or dynamic coefficient of friction μ₁And a first force F perpendicular to the first contact surface 1022_N1And the second body 1020 has a second coefficient of static or dynamic friction mu₂And a second force F perpendicular to the second contact surface 1024_N2. Further, the first body 1018 may haveFirst moment of inertia J₁And the second body 1020 may have a second moment of inertia J₂. In some embodiments, the first coefficient of static or dynamic friction, μ₁First normal force F_N1And a first moment of inertia J₁Is selected to be different from the second static or dynamic coefficient of friction, mu, respectively₂A second normal force F_N2And a second moment of inertia J₁. Accordingly, the damping system 1000 may be configured to account for a plurality of different modal modes at substantially a single location along the downhole system 1002.

Turning now to fig. 11, a schematic diagram of a damping system 1100 according to one embodiment of the present disclosure is shown. The damping system 1100 may operate in a similar manner as shown and described above. However, in this embodiment, the second element 1112 mounted to the first element 1110 of the downhole system 1102 is formed from a first body 1118, a second body 1120, and a third body 1128. The first body 1118 has a first contact surface 1122 between the first body 1118 and the first element 1110, the second body 1120 has a second contact surface 1124 between the second body 1120 and the first element 1110, and the third body 1128 has a third contact surface 1130 between the third body 1128 and the first element 1110. As shown, the third body 1128 is positioned between the first body 1118 and the second body 1020. In this embodiment, the three

bodies

1118, 1120, 1128 are in contact with each other, and thus may have a normal force and a static or dynamic coefficient of friction therebetween.

Contact between the three

bodies

1118, 1120, 1128 may be established, maintained or supported by a resilient connecting element (such as a spring element) between two or more of the

bodies

1118, 1120, 1128. Additionally or alternatively, the first body 1118 may have a first static or dynamic coefficient of friction μ at the first contact surface 1122₁And a first force F_N1The second body 1120 may have a second coefficient of static or dynamic friction μ at the second contact surface 1124₂And a second force F_N2And the third body 1128 may have a third coefficient of static or dynamic friction μ at the third contact surface 1130₃And a third force F_N3。

Additionally or alternatively, the first and

third bodies

1118, 1128 may have a fourth force F between each other at the contact surface between the first and

third bodies

1118, 1128_N13And a fourth coefficient of static or dynamic friction mu₁₃. Similarly, the third body 1128 and the second body 1120 may have a fifth force F between each other at a contact surface between the third body 1128 and the second body 1120_N32And a fifth coefficient of static or dynamic friction mu₃₂。

In addition, the first body 1118 may have a first moment of inertia J₁The second body 1120 may have a second moment of inertia J₂And the third body 1128 may have a third moment of inertia J₃. In some embodiments, the coefficient of static friction or the coefficient of dynamic friction μ₁、μ₂、μ₃、μ₁₃、μ₃₂Force F_N1、F_N2、F_N3、F₁₃、F₃₂And moment of inertia J₁、J₂、J₃May be selected to be different from each other such that the product μ is for at least a sub-range of relative velocities of the first element 1110, the first body 1118, the second body 1120, and the third body 1128_i·F_i(wherein i ═ 1, 2, 3, 13, 32) are different. Furthermore, the static or dynamic coefficient of friction and the normal force between adjacent bodies may be selected to achieve different damping effects.

While shown and described with respect to a limited number of embodiments and specific shapes, relative sizes, and numbers of elements, those skilled in the art will appreciate that the damping system of the present disclosure may take on any configuration. For example, the shape, size, geometry, radial arrangement, contact surfaces, number of bodies, etc. may be selected to achieve a desired damping effect. While in the arrangement shown in fig. 11, the first and

second bodies

1118, 1120 are coupled to one another by frictional contact with the third body 1128, such arrangement and description is not limiting. The coupling between the first and

second bodies

1118, 1120 may also be created by a hydraulic, electrical, or mechanical coupling device or mechanism. For example, the mechanical coupling between the first body 1118 and the second body 1120 may be created by a rigid or elastic connection of the first body 1118 and the second body 1120.

Turning now to fig. 12, a schematic diagram of a damping system 1200 is shown, according to one embodiment of the present disclosure. The damping system 1200 may operate in a similar manner as shown and described above. However, in this embodiment, the second element 1212 portion of the damping system 1200 is fixedly attached or connected to the first element 1210. For example, as shown in this embodiment, the second element 1212 has a fixed portion 1232 (or fixed end) and a movable portion 1234 (or movable end). The fixed portion 1232 is fixed to the first element 1210 along a fixed connection 1236, and the movable portion 1234 is in frictional contact with the first element 1210 across a contact surface 1214 (similar to the first element 1010 being in frictional contact with the second element 1012 described with respect to fig. 10).

The movable portion 1234 may have any desired length that may be associated with the mode shape shown in fig. 9B. For example, in some embodiments, the movable portion may be longer than one tenth of the distance between the maximum and minimum values of any modal shape that may have been calculated for a particular drilling assembly. In another example, in some embodiments, the movable portion may be longer than one quarter of the distance between the maximum and minimum values of any modal shape that may have been calculated for a particular drilling assembly. In another example, in some embodiments, the movable portion may be longer than half the distance between the maximum and minimum values of any modal shape that may have been calculated for a particular drilling assembly. In another example, in some embodiments, the movable portion may be longer than the distance between the maximum and minimum values of any modal shape that may have been calculated for a particular drilling assembly.

Thus, even though the exact location of modal maxima or minima may not be known during downhole deployment, it may be ensured that the second element 1212 is in frictional contact with the first element 1210 at the location of maximum amplitude to achieve optimal damping. Although shown using a particular arrangement, those skilled in the art will appreciate that other arrangements of the partially secured first element are possible without departing from the scope of the present disclosure. For example, in one non-limiting embodiment, the fixed portion can be in a more central portion of the first element such that the first element has two movable portions (e.g., at opposite ends of the first element). As can be seen in fig. 12, the movable portion 1234 of the second element 1212 is substantially elongated and may cover a portion of the modal shape (such as the

modal shapes

902, 904, 906 in fig. 9B) corresponding to the length of the movable portion 1234 of the second element 1212. The elongated second element 1212 in frictional contact with the first element 1210 may be preferred over a shorter second element because the shorter second element may be located in an undesired portion of the mode shape, such as in a damping position 910 where the second mode shape 904 is small or even zero, as explained above with respect to fig. 9B. Utilizing an elongated second element 1212 may ensure that at least a portion of the second element is at a distance from a location where one or more of the mode modes are zero or at least close to zero. Fig. 13-19 and 21-22 show a further variety of elongated second elements in frictional contact with the first elements. In some embodiments, the elongated second member may be resilient such that the movable portion 1234 is able to move relative to the first member 1210, while the fixed portion 1232 is stationary relative to the first member 1210. In some embodiments, the second element 1212 may have multiple contact points at multiple locations of the first element 1210.

In the above-described embodiments, and in the damping system according to the present disclosure, the first element is temporarily fixed to the second element due to the frictional contact. However, when the vibration of the downhole system increases and exceeds a threshold, for example when the inertial force exceeds the static friction force, the first element (or part thereof) moves relative to the second element, thus providing damping. That is, when HFT0 increases above a predetermined threshold (e.g., a threshold for amplitude, distance, velocity, and/or acceleration) within the downhole system, the damping system will operate automatically, thus embodiments provided herein include a passive damping system. For example, embodiments include a passive damping system that operates automatically without the use of additional energy, and therefore does not utilize additional energy sources.

Turning now to fig. 13, a schematic diagram of a damping system 1300 according to an embodiment of the present disclosure is shown. In this embodiment, the damping system 1300 includes one or more elongated

first elements

1310a, 1310b, 1310c, 1310d, 1310e, 1310f, each of which is disposed within and in contact with a second element 1312. Each of the

first elements

1310a, 1310b, 1310c, 1310d, 1310e, 1310f may have a length in the axial tool direction (e.g., in a direction perpendicular to the cross-section shown in fig. 13) and optionally a fixation point where the respective

first element

1310a, 1310b, 1310c, 1310d, 1310e, 1310f is fixed to the second element 1312. For example, the

first elements

1310a, 1310b, 1310c, 1310d, 1310e, 1310f may be fixed at respective upper ends, middle portions, lower ends, or multiple fixing points of different

first elements

1310a, 1310b, 1310c, 1310d, 1310e, 1310f, or multiple points given a single

first element

1310a, 1310b, 1310c, 1310d, 1310e, 1310 f. Further, as shown in fig. 13, the

first element

1310a, 1310b, 1310c, 1310d, 1310e, 1310f may optionally be biased or engaged to the second element 1312 by a biasing element 1338 (e.g., by a biasing spring element or biasing actuator applying a force having a component toward the second element 1312). Each of the

first elements

1310a, 1310b, 1310c, 1310d, 1310e, 1310f may be arranged and selected to have the same or different normal forces, static or dynamic coefficients of friction, and mass moments of inertia, thereby enabling various damping configurations.

In some embodiments, the first element may be substantially uniform in material, shape, and/or geometry along its length. In other embodiments, the first element may vary in shape and geometry along its length. For example, referring to fig. 14, a schematic diagram of a damping system 1400 is shown, according to an embodiment of the present disclosure. In this embodiment, first element 1410 is disposed relative to second element 1412, and first element 1410 has a tapered and/or helical arrangement relative to second element 1412. Thus, in some embodiments, a portion of the first or second element may change geometry or shape along its length relative to the second element, and such changes may also occur in a circumferential span around or relative to the second element and/or relative to the tool body or downhole system.

Turning now to fig. 15, a schematic diagram of another damping system 1500 in accordance with an embodiment of the present disclosure is shown. In the damping system 1500, the first element 1510 is a toothed (threaded) body that fits within a threaded second element 1512. Contact between the teeth (threads) of the first element 1510 and the threads of the second element 1512 may provide frictional contact between the two

elements

1510, 1512 to achieve damping as described herein. Due to the inclined surface of the first element 1510, the first element 1510 will start to move under axial and/or torsional vibrations. Further, movement of the first element 1510 in the axial or circumferential direction will also produce movement in the circumferential or axial direction, respectively, in this configuration. Thus, with the arrangement shown in fig. 15, axial vibrations may be used to mitigate or dampen torsional vibrations, and torsional vibrations may be used to mitigate or dampen axial vibrations. The locations at which the axial and torsional vibrations occur may be different. For example, while axial vibrations may be evenly distributed along the drilling assembly, torsional vibrations may follow modal mode patterns as discussed above with respect to fig. 9A-9B. Thus, regardless of where the vibration occurs, the configuration shown in FIG. 15 can be used to damp torsional vibration using axial vibration induced movement of the first element 1510 relative to the second element 1512 (or vice versa). As shown, an optional fastening element 1540 (e.g., a bolt) may be used to adjust the contact pressure or normal force between the two

elements

1510, 1512, thus adjusting the frictional and/or other damping characteristics of damping system 1500.

Turning now to fig. 16, a schematic diagram of a damping system 1600 according to an embodiment of the present disclosure is shown. Damping system 1600 includes a first element 1610, which is a rigid rod, secured at one end within a second element 1612. In this embodiment, the rod end 1610a is arranged to frictionally contact the second element stop 1612a, thus providing damping as described in accordance with embodiments of the present disclosure. The normal force between the rod end 1610a and the second element stop 1612a may be adjusted, for example, by a threaded connection between the rod end 1610a and the first element 1610. Furthermore, the stiffness of the rod may be selected to optimise damping or to influence the mode shape in a beneficial manner to provide greater relative displacement. For example, selecting a rod with lower stiffness will result in higher amplitude and higher energy dissipation of the torsional oscillation of the first element 1610.

Turning now to fig. 17, a schematic diagram of a damping system 1700 according to an embodiment of the present disclosure is shown. The damping system 1700 includes a first element 1710 frictionally attached or connected to a second element 1712 that is arranged as a rigid rod and fixedly connected (e.g., by welding, screwing, brazing, adhering, etc.) to an external tubular 1714, such as a drill collar, at a fixed connection 1716. In one aspect, the rod may be a tube that includes electronics, power sources, storage media, batteries, microcontrollers, actuators, sensors, etc. that are susceptible to wear from HFTO. That is, in one aspect, the second element 1712 may be a probe, such as a probe that measures directional information, including one or more of a gravimeter, a gyroscope, and a magnetometer. In this embodiment, the first element 1710 is arranged to frictionally contact, move relative to, and along the fixed rod structure of the second element 1712, or oscillate, thus providing damping as described in accordance with embodiments of the present disclosure. Although the first element 1710 is shown in fig. 17 as being relatively small compared to the damping system 1700, it is not intended to be limiting in this regard. Accordingly, first element 1710 can be any size and can have the same outer diameter as damping system 1700. Further, the position of the first element 1710 may be adjustable to move the first element 1710 closer to the mode shape maximum to optimize damping mitigation.

Turning now to fig. 18, a schematic diagram of a damping system 1800 is shown, according to one embodiment of the present disclosure. The damping system 1800 includes a first element 1810 frictionally movable along a second element 1812. In this embodiment, the first element 1810 is arranged with a resilient spring element 1842 (such as a coil spring or other element or means) to engage the first element 1810 with the second element 1812, thus providing a restoring force when the first element 1810 has moved and deflected relative to the second element. The restoring force is directed to reduce deflection of the first element 1810 relative to the second element 1812. In such embodiments, the resilient spring element 1842 may be arranged or tuned to a resonance and/or critical frequency (e.g., the lowest critical frequency) of the resilient spring element 1842 or an oscillating system comprising the first element 1810 and the resilient spring element 1842.

Turning now to fig. 19, a schematic diagram of a damping system 1900 is shown, according to one embodiment of the present disclosure. The damping system 1900 includes a first element 1910 that is frictionally moveable about a second element 1912. In this embodiment, the first element 1910 is arranged with a first end 1910a having a first contact (e.g., a first end normal force F)_NiFirst end static or dynamic coefficient of friction mu_iAnd first end moment of inertia J_i) And has a second contact (e.g., second end normal force F) at second end 1910b_NiSecond end coefficient of static or dynamic friction mu_iAnd second end moment of inertia J_i). In some such embodiments, the types of interactions between the respective first end 1910a or second end 1910b and the second element 1912 may have different physical characteristics. For example, one or both of the first end 1910a and the second end 1910b may have a stick contact/engagement and one or both may have a slip contact/engagement. The arrangement/configuration of the first end 1910a and the second end 1910b can be set to provide damping as described in accordance with embodiments of the present disclosure.

Advantageously, embodiments provided herein relate to a system for mitigating High Frequency Torsional Oscillations (HFTO) of a downhole system by applying a damping system mounted on a rotating tubular string (e.g., a downhole tubular string or drill string). The first element of the damping system is at least partially frictionally coupled for circumferential movement relative to the axis of the drill string (e.g., frictionally coupled for rotation about the axis of the drill string). In some embodiments, the second element may be part of a drilling system or bottom hole assembly and need not be a separately installed component or weight. The second member, or a portion thereof, is connected to the downhole system in a manner such that relative motion between the first and second members has zero or near zero relative velocity (i.e., no relative motion or slow relative motion) in the absence of HFTO. However, when HFTO occurs above different acceleration values, relative movement between the first and second elements is possible and alternating positive and negative relative velocities are achieved. In some embodiments, the second element may be a mass or weight connected to the downhole system. In other embodiments, the second element may be a portion of a downhole system (e.g., a portion of a drilling system or BHA, such as the remainder of the downhole system that provides the functionality described herein) with friction between the first element and the second element.

As noted above, the second element of the damping system is selected or configured such that when there is no vibration (i.e., HFTO) in the drill string, the second element will frictionally connect to the first element through static friction. However, when vibration (HFTO) is present, the second member moves relative to the first member and reduces the frictional contact between the first and second members as described above with respect to fig. 2, such that the second member can rotate (move) relative to the first member (and vice versa). The first and second elements effect energy dissipation when in motion, thereby mitigating HFTO. The damping system, in particular the first element thereof, has a position, weight, external force and dimensions to achieve damping at one or more specific or predefined vibrational modes/frequencies. As described herein, the first element is fixedly connected in the absence of HFTO vibration, but is then able to move in the presence of certain accelerations (e.g., according to a HFTO modality), thus damping of HFTO is achieved by a zero crossing of relative speed (e.g., switching between positive and negative relative rotational speeds).

In the various configurations discussed above, sensors may be used to estimate and/or monitor the efficiency of the damper and the dissipated energy. Measurements of displacement, velocity and/or acceleration near the contact point or surface of the two interacting bodies, for example in combination with force or torque sensors, can be used to estimate the relative motion and calculate the dissipated energy. For example, when the two interacting bodies are engaged by a biasing element (such as a spring element or an actuator), the force may also be known without measurement. The dissipated energy can also be derived from the temperature measurement. Such measurements may be communicated to a controller or operator so that parameters such as normal force and/or static or dynamic coefficient of friction may be adjusted to achieve higher dissipated energy. For example, the measured and/or calculated values of displacement, velocity, acceleration, force, and/or temperature may be sent to a controller (such as a microcontroller) having an instruction set stored to a storage medium that adjusts and/or controls at least one of a force and/or a coefficient of static or dynamic friction that engages the two interacting bodies based on the instruction set. Preferably, the adjustment and/or control is done while the drilling process is in progress to achieve optimal HFTO damping results.

While the embodiments described herein have been described with reference to specific drawings, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular instrument, situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that the disclosure will include all embodiments falling within the scope of the appended claims or the following description of possible embodiments.

Severe vibrations in drill strings and bottom hole assemblies can be caused by cutting forces at the drill bit or mass imbalance in downhole tools, such as drilling motors. Among other negative effects are reduced rate of penetration, reduced measurement quality and downhole failures.

There are different kinds of torsional vibrations. In the literature, torsional vibrations are mainly distinguished by stick/slip and High Frequency Torsional Oscillations (HFTO) of the entire drilling system. Both are primarily stimulated by self-excitation mechanisms that occur due to the interaction of the drill bit with the formation. The main differences between stick/slip and HFTO are frequency and typical mode shape: the frequency is higher than 50Hz for HFTO, compared to lower than 1Hz for stick/slip. Furthermore, the stimulated modal shape of stick/slip is the first modal shape of the entire drilling system, while the modal shape of HFTO is typically limited to a small portion of the drilling system and has a relatively high amplitude at the drill bit.

Due to the high frequency, HFTO corresponds to high acceleration and torque values along the BHA and may have damaging effects on electronics and mechanical components. Based on the theory of self-excitation, increased damping can mitigate HFTO (due to self-excitation instability and can be interpreted as negative damping of the associated mode) if a certain limit of the damping value is reached.

One damping concept is based on friction. Friction between two components in the BHA or drill string may dissipate energy and reduce the level of torsional oscillations.

Based on this concept, the design principle that the inventors consider to be most suitable for damping due to friction is discussed. Damping should be achieved by friction, where the operating point of friction versus relative velocity must be around point 204 shown in fig. 2. This operating point will cause high energy dissipation due to the friction hysteresis achieved, while point 202 of fig. 2 will cause energy input into the system.

As discussed above, the frictional forces between the drilling system and the borehole do not create significant additional damping in the system. This is because the relative velocity between the contact surfaces (e.g., stabilizer and bore hole) does not have a zero average. The two interacting bodies of the friction damper must have an average speed or rotational speed relative to each other that is small enough for the HFTO to cause a sign shift of the relative speed of the two interacting bodies of the friction damper. In other words, the maximum value of the relative velocity between the two interacting bodies generated by HFTO needs to be higher than the average relative velocity between the two interacting bodies.

Energy dissipation occurs only during the slip phase via the interface between the damping apparatus and the drilling system. The sliding occurs in the following situations: inertial forces exceed the limit between stick and slip (i.e., stiction): f_R＞μ₀·F_N(where the static friction is equal to the static coefficient of friction times the normal force between the two contact surfaces). The normal force and/or the static or dynamic coefficient of friction may be adjustable to achieve an optimal or desired energy consumptionDispersing. Adjusting the normal force and at least one of the static or dynamic coefficients of friction may improve the energy dissipation caused by the damping system.

As discussed herein, the arrangement of the friction dampers should be in the region of high HFTO acceleration, load and/or relative motion. Because different modalities may be affected, designs that can mitigate all HFTO modalities are preferred (e.g., fig. 9A and 9B).

Equivalents may be used as the friction damper tool of the present disclosure. Slotted drill collars 2100 may be used, as shown in FIGS. 21 and 22. A cross-sectional view of the slotted drill collar 2100 is shown in fig. 22. In one non-limiting embodiment, the slotted drill collar 2100 has high flexibility and will cause higher deformation without the addition of the friction device 2102. Higher speeds will cause higher centrifugal forces, which will push the friction device 2102 to press into the slot with an optimized normal force to allow high friction damping. Other factors that may be optimized in this configuration are the number and geometry of the slots and the geometry of the damping device. The additional normal force may be applied by the spring element 2104 (shown in fig. 22), discussed above, by an actuator, and/or by centrifugal force.

The advantage of this principle is that the friction device will be installed directly into the force flow. The torsion of the drill collar due to the excited HFTO mode and the corresponding mode shape will be supported in part by the friction device, which will move up and down during one cycle of vibration. High relative motion together with an optimized coefficient of friction and normal force will cause high energy dissipation.

The goal is to prevent the amplitude of the HFTO amplitude (in this case represented by the tangential acceleration amplitude) from increasing. The (modal) damping that must be added to each unstable torsional mode by the friction damper system needs to be higher than the energy input in the system. The energy input does not occur instantaneously, but rather occurs over multiple cycles until the worst case amplitude (zero RPM at the drill bit) is reached.

According to this concept, relatively short drill collars can be used because the friction dampers use relative motion along the distance from the drill bit. There is no need to have high tangential acceleration amplitude, but only some deflection ("twist") of the drill collar, which will be achieved almost everywhere along the BHA. The drill collar and damper should have a similar mass-to-stiffness ratio ("impedance") as compared to the BHA. This will allow the mode shape to propagate in the friction drill collar. A high damping will be achieved which will mitigate the HFTO with adjustment of the parameters discussed above (normal force due to the spring etc.). An advantage compared to other friction damper principles is that the friction device is applied directly to the force flow of the HFTO mode deflection. The relatively high relative speed between the friction device and the drill collar will cause high energy dissipation.

The damper will have a high efficiency and be effective for different applications. HFTO causes high costs due to extensive repair and maintenance work, reliability problems with non-productive time, and small market share. The proposed friction damper will work below the motor (decoupling HFTO) and also above the motor. It may be installed in every place of the BHA, which would also include an arrangement above the BHA if the modal shape propagated to that point. If the mass and stiffness distributions are relatively similar, the modal shape will propagate through the entire BHA. The optimal arrangement may be determined, for example, by a torsional oscillation advisor (torsional oscillation advisor) that allows the calculation of the critical HFTO mode and corresponding mode shape.

Further, as described above, one location of the damper as described herein may be within the drill bit due to high vibration amplitudes at the drill bit. That is, according to some embodiments of the present disclosure, the damper may be integrated into and be part of a drill bit or other fracturing apparatus. In such embodiments, the distance to the drill bit is zero or substantially zero. Incorporating a damper/dampener element in the drill bit may impose a limit on the axial length of the damper/dampener element. However, because the damping is high due to the high amplitude of the mode shape at or near the drill bit, the damper/damper element may be relatively short and still achieve a sufficient damping effect. The damper at or in the drill bit may be less than 30cm, or 40cm, or 50cm, or 100cm, or 150 cm.

In some such embodiments, the damper may be formed from a mass or inertia (inertia) coupled to the drill bit solely by a damping force or a damping torque. The damping force may be generated, for example, but not limited to, by viscous damping, frictional damping, hydraulic damping, magnetic damping (e.g., eddy current damping), piezoelectric (shunt) damping, and the like. In some such embodiments, the damper may be combined with a spring that will enable a tuned mass damper or a tuned friction damper. In these cases, the eigenfrequency of the damper will be tuned to the eigenfrequency of the mode that should be damped.

As discussed above, analysis has shown that damping increases proportionally with effective rotational inertia and increases quadratically with mass normalized mode shape at the drill bit. The additional constant factor depends on the type of damping. Further frictional damping with inertial dampers is theoretically frequency independent and hydraulic dampers have a certain frequency dependence. This trade-off is also applicable to other types of damping and can be influenced using different parameters of force (e.g., by harmonically adjusting the normal force of the friction damper configuration, choosing a fluid with properties that vary with the relative velocity of the components, etc.). As noted, the drill bit or other fracturing device is one location for using inertial dampers, which may be advantageous because critical modes typically have maximum amplitude at the drill bit (e.g., as shown in fig. 9B). One exemplary critical mode is at 248Hz with maximum amplitude at the drill bit, but various other modes/frequencies may be critical based on the particular configuration and downhole operation. That is, the critical modality may depend on various considerations, and for purposes of explanation only the 248Hz modality is described as an example. It is important to note that excitability also increases quadratically with the amplitude of the mode shape at the drill bit in theory. In addition, the amount of damping required to mitigate vibration may also increase quadratically with the modal shape at the drill bit.

In one non-limiting embodiment of the damper positioned at the drill bit, the friction damper may be a closed ring of any mode shape connected to the drill bit and configured to rotate torsionally. In another embodiment, the damper positioned at the drill bit may be a linear mass that is connected at the drill bit in a tangential direction and is effective to induce a rotational force. Several individual dampers may be installed and deployed around the drill bit or other fracturing equipment (i.e., at the end of the drill string). In another configuration, the damper may be formed by two positively connected parts of the drill bit connected to different axial positions of the drill bit. The connection at different axial positions results in a relative movement between the two positively connected parts. Examples of such configurations may include, for example, threaded connections with opposing contact surfaces. The drill bit may be a fixed cutter drill bit such as a polycrystalline diamond cutter ("PDC"), diamond, or impregnated bit, or a roller bit such as a roller cone drill bit, or a hybrid drill bit.

For example, turning to fig. 23, a schematic diagram of a fragmentation device 2300 is shown. The fracturing apparatus 2300 includes a plurality of blades 2302. Each of the blades 2302 is configured to cut material (e.g., rock) of a formation during a drilling operation. As shown, each blade 2302 includes a respective damper element 2304. The schematic illustration of fig. 23 is a schematic end view in which the axial length of the fragmentation device 2300 extends into and out of the page. In one non-limiting example, damper elements 2304 may each have a length L-0.08 m and 15000kg/m in the axial direction²The density of (c). Damper element 2304 is arranged for mass normalized mode shape amplitudes of 0.6, 0.8, 0.9, 1, and 1.1. The damping achieved varies from about 0.1% and 0.32%. Analysis has shown that for a critical mode shape of 248Hz with an amplitude of 1.1 at the fragmentation device 2300, the necessary damping is about 0.2%. Note that the damper element 2304 has a relatively small inertial mass sufficient to limit the amplitude associated with HFTO and thus reduce vibration of the downhole tool having the fracturing apparatus 2300.

In some embodiments, a pure rotary damper may be installed within the drill bit shank, and such a configuration would also benefit from high modal mode amplitudes at the drill bit. However, such mounting may result in a smaller radial position of the damper element. Thus, a smaller radius of the inertia member will limit the damping effect, but this can be compensated by the fact that a higher mass can be placed at the drill bit shank. That is, the selection of the mass and radial position relative to the central axis of the fragmentation device may be determined based on the desired vibration or mode shape to be damped.

By positioning the damper element within or at the drill bit or other fracturing device, a sufficient amount of damping can be achieved to minimize or eliminate downhole vibrations. The reason is that in almost all cases, the mass normalized mode amplitude is greatest at the drill bit or the fracturing equipment. This can be physically explained by the fact that: if the velocity at the drill bit is assumed to weaken the torque characteristics with respect to the average rotational velocity, the excitability and likelihood of the excited mode also increases quadratically with the amplitude of the mode shape at the drill bit.

One type of damper element that may be installed within a fracturing apparatus in accordance with the present disclosure is a linear viscous damper. Such a damper element would include a mass and force element that transmits force from the drill bit to the mass/inertia member. Such a damper element would have a force element directed, arranged or oriented to the tangential direction to damp the HFTO. The force element may be a linear viscous or frictional damping element as will be understood by those skilled in the art in light of the teachings herein.

Turning now to fig. 24, a schematic diagram of a drill bit-based damping system 2400 is shown, according to one embodiment of the present disclosure. Drill bit-based damping system 2400 includes a drill bit 2402 and one or more damper elements 2404. The drill bit 2402 has a bit body 2406 and an attachment portion 2408 for attaching and engaging a tubular string (e.g., a drill string). A bit shank 2410 extends between the attachment portion 2408 and the bit body 2406. The bit body 2406 is configured to enable cutting, breaking, or fracturing of materials in a downhole formation in order to form a borehole or wellbore. Mounted to drill bit 2402 are one or more dampener elements 2404. The damper element 2404 of this embodiment is mounted to a drill bit shank 2410.

In this embodiment, damper element 2404 is formed of three separate elements to achieve a damping effect. The first element 2412 is in direct contact with the bit shank 2410, and in some embodiments may be an axial wave spring housing. External to the first element 2412 is a second element 2414, which may be a radial friction surface housing. Forming the outer or outermost component of damper element 2404 is a third element 2416, which may be an inertia bar housing. During operation, third element 2416 (inertia handle housing) may move relative to second element 2414 (radial friction surface housing) and/or first element 2412 (axial wave spring housing). Such relative movement may be achieved during a particular mode, and thus vibration damping, as described above. Thus, the first, second, and

third elements

2412, 2414, 2416 form a damper inertia ring disposed about the bit shank 2410.

In some embodiments, as shown in fig. 24, the damper inertia ring installed in/on or near the bit shank may be mud lubricated or covered by an optional cap sleeve 2418. The cover sleeve 2418 may be disposed about the third element 2416 to protect the contact area from mud and thus allow for more controlled application of normal forces and coefficients of friction. In some embodiments, the cover sleeve 2418 may be omitted and the inertial mass may be increased, which will significantly increase the achievable damping. In some embodiments of the present disclosure, the contact surface providing frictional damping may need to be robust, for example, utilizing polycrystalline diamond cutters, copper, sintered materials, or materials for fracture design, as understood by those skilled in the art. In some embodiments, optional bearings may be used in the radial direction to ensure rotational movement of the damper inertia ring (e.g., damper elements 2404 shown in fig. 24).

As noted, damper element 2404 can be a single or multiple elements/structures. For example, the inertia ring itself may be a closed or interrupted ring, such as a half shell. In some embodiments, half shells may be employed when the full ring cannot be enabled due to the drill bit design or configuration. The housing halves may be assembled around radial friction contacts or radial bearings that may be arranged relative to and similar in position and mode to first and

second elements

2412, 2414 of damper element 2404 shown in fig. 24. The bearings may also be split to allow installation. The normal force may also be applied by the half shells controlled by their resilience and the applied normal/connection force. The radial wave spring housing may also be used to apply radial frictional forces between the inertia half housing and the radial friction surface housing.

Different geometries may be employed for the damper element (e.g., inertia ring) which may be advantageous to increase inertia. In this sense, the density of the material selected for the damper element may be selected as high as possible, such that the radius of the mass distribution is on a large radius with respect to the axial axis of the drilling system or drill bit. The inertia member (or inertia half housing) may incorporate an additional mass (inertia member) preferably mounted behind the blade to prevent flow disruption. The diameter of the ring behind the blade may be higher than if the cutting flow required a low diameter.

Turning to fig. 25, a schematic diagram of a fragmentation device 2500 is shown. The fragmentation device 2500 includes a plurality of blades 2502. Each of blades 2502 is configured to cut material of the formation (e.g., rock) during drilling operations. In this embodiment, rather than incorporating the dampener element directly into the blade as shown and described with respect to fig. 23, a single ring dampener element 2504 is disposed about the bit shank or other part of the fracturing apparatus 2500. The schematic illustration of fig. 25 is a schematic end view in which the axial length of the fragmentation device 2500 extends into and out of the page. In this embodiment, the dampener element 2504 is an inertia ring, similar to that shown and described with respect to fig. 24, but positioned adjacent to and oriented with respect to the blade 2502. As shown, the dampener element 2504 can include one or more mass structures 2506, which can be disposed behind or relative to one or more of the blades 2502. The mass structure 2506 may be selected and configured to enable damping of vibrations of the fragmentation device 2500.

In some embodiments, a limit stop may optionally be provided to prevent the ring-configured damper element from moving freely or continuously (e.g., over 10 ° of rotation). The normal force between the damper element and the bit shank or other part of the drill bit may be applied radially or axially by a spring or other mechanism. The radial friction force can be achieved by a spring or by the elastic design of the ring damper element. In some such embodiments, the double-half shell damper element may be pre-stressed to achieve a desired frictional force. The axial normal force may be achieved by a spring, wherein the weight of the mass/inertia in the vertical bore and the spring may be constructed from a housing or the like. The material of the drill bit may be a steel body bit or a matrix bit. The axial bearing may be used to decouple the potential normal force spring stack from rotational movement of the inertial mass.

In some embodiments, tangential damper elements may be employed within blades of drill bits or other fracturing equipment. Dampers for tangential damping may be mounted in locations having a high radius relative to the axial axis of the drilling system.

In the case of dampers mounted to move freely in the tangential direction (direction of tangential acceleration), a (steel) tube screwed into the blade can be used. The tangential damper may be assembled into the tube, incorporating a mechanism to apply a normal force between the inertial mass and the tube or bit body, preferably orthogonal to the tangential direction. In some embodiments, the tangential damper element may be mounted, for example by a threaded connection, into a corresponding housing or portion thereof that may be secured to a blade of the fracturing apparatus. The housing may have any geometry that is mountable to the blade.

Turning to fig. 26, a schematic of a drill bit-based damping system 2600 is shown. The drill bit 2602 is arranged with a ring-type damper element 2604, similar to that shown and described above with respect to fig. 24. The drill bit 2602 has a bit body 2606 and an attachment portion 2608 for attachment and engagement with a tubular string (e.g., a drill string). The bit shank 2610 extends between the attachment portion 2608 and the bit body 2606. The bit body 2606 is configured to enable cutting, breaking, or fracturing of materials in a downhole formation in order to form a borehole or wellbore. Accordingly, the bit body 2606 may include one or more blades to perform a cutting action. The ring-type damper member 2604 is mounted to the bit shank 2610 and may be a complete hoop structure formed from a single piece or two or more pieces.

The drill bit-based damping system 2600 additionally includes one or more blade-type damper elements 2620. The blade-type damper element 2620 is configured to be mounted within or to a blade of the drill bit 2602. The blade-type damper element 2620 may be a tangential damper. The blade-type damper elements 2620 for tangential damping may be installed into locations having a high radius relative to the axial axis of the drilling system (e.g., within the radial tips of the blades or inserts). In some embodiments, the blade-type damper element 2620 may be mounted and free to move in a tangential direction (i.e., the direction of tangential acceleration). To accomplish this, a tube (e.g., formed of steel) may be threaded into the blade. The blade-type damper elements 2620 may then be assembled into a tube or other housing structure, incorporating a mechanism that applies a normal force between the inertial mass and the tube or bit body 2606. In some embodiments, such mounting may be orthogonal to the tangential direction. The housing structure may have a blade or any geometry in the blade that may be mounted to the fracturing device 2602.

Turning now to fig. 27-28, schematic views of

damper elements

2700, 2800 are shown. As described above, the

damper elements

2700, 2800 are configured for installation within a blade of a chipping device. Each

damper element

2700, 2800 includes a

respective housing

2702, 2802 for housing and containing the components of the

respective damper element

2700, 2800. The first damper element 2700 has a substantially rectangular geometry (with curved corners) and the second damper element 2800 has a substantially circular geometry. The

housings

2702, 2802 are configured to fit into blades of a fracturing device (e.g., as shown in fig. 26).

The

damper elements

2700, 2800 each include a

mass element

2704, 2804 movably mounted within a

housing

2702, 2802. The

mass elements

2704, 2804 are arranged between the mounting

elements

2706, 2806 and the

contact elements

2708, 2808. The mounting

elements

2706, 2806 are configured to apply a force on the

respective mass element

2704, 2804 towards the

contact element

2708, 2808. Thus, frictional contact may be achieved between the respective

mass elements

2704, 2804 and the

contact elements

2708, 2808. The

mass elements

2704, 2804 may be arranged within the

respective housings

2702, 2802 together with one or more limit stops 2710, 2810. The limit stops 2710, 2810 may include optional stiffness or hydraulic elements for damping movement of the

mass elements

2704, 2804,

furthermore, the limit stops 2710, 2810 may prevent the

mass elements

2704, 2804 from getting stuck in one edge of the

housings

2702, 2802. The limit stops 2710, 2810 may be configured with springs or other elements to avoid damaging the

mass elements

2704, 2804 and to urge the

mass elements

2704, 2804 toward an intermediate or rest position relative to the housing. In some embodiments, it may be advantageous to optimize the spring rate and/or

gap

2711, 2811 in the

housings

2702, 2802 to allow the

mass elements

2704, 2804 to move within the

housings

2702, 2802. The

damper elements

2700, 2800 can be arranged as inserts (e.g., the

housings

2702, 2802 are configured for installation). The

insertable damper elements

2700, 2800 can be mounted such that the

mass elements

2704, 2804 are placed at locations with high radii relative to the axis of the drilling system to increase rotational inertia.

The mounting

elements

2706, 2806 are configured to exert a normal force on the

mass elements

2704, 2804. For example, the mounting

elements

2706, 2806 may be arranged as spring housings to push the

mass elements

2704, 2804 into contact with the

contact elements

2708, 2808. Further, the mounting

elements

2706, 2806 and/or the

contact elements

2708, 2808 may be configured to control the tangential movement of the

mass elements

2704, 2804 to enable damping of the HFTO. In some embodiments, the mounting

elements

2706, 2806 push the

mass elements

2704, 2804 into contact with the

contact elements

2708, 2808 to create a frictional force. The friction is applied, for example, by a material that is advantageous with respect to the coefficient of friction and the expected wear that should be as low as possible.

According to embodiments of the present disclosure, the integration of damping into a drill bit may be achieved. Damping may be applied by any axial, tangential and/or radial force or corresponding torque capable of dissipating energy. In the case of coupled modes, the damping force in the axial direction can also dissipate energy from the torsional direction. The coupling may also be achieved kinetically, such as through drill bit rock interaction. As described for frictional damping, the contact surface to which the coefficient of friction and normal force are applied may be optimized and/or selected for damping one or more critical modes. In some embodiments, advantageous materials or designs may be employed to prevent wear (e.g., copper or polycrystalline diamond cutters). Multiple contacts with different properties may be used to tune the system to a favorable coefficient of friction or characteristic.

Another form of damping that may be employed is hydraulic damping. Such hydraulic damping may be achieved by systems located in the drill tip or other locations arranged around the drill bit or the fragmenting device or in these other locations. In some such embodiments, a viscous fluid (e.g., a viscous fluid in a chamber) may be arranged and mounted in a position similar to that described above. In some such applications, the (shear) stress in the fluid between the inertia ring/mass and the drill bit/drilling system may be selected to achieve tangential acceleration (damping) forces and associated harmonic movement to damp HFTO. In the case of ring shear, the fluid provides a damping force between the inertia ring and the bit. In this case, the ring may require a well-defined geometry that closes the housing and potentially the gap between the ring and the housing. In hydraulic damping, viscous damping forces are sensitive to changes in the parameters of the gap and the viscous fluid. Therefore, a fluid that is not temperature sensitive may be preferred. Fluids with different shear stresses that vary with shear rate can be used to achieve advantageous behavior. Some such exemplary fluids include, but are not limited to, newtonian fluids, dilatants (e.g., shear thickening fluids), pseudoplastomers, bingham plastomers, bingham pseudoplastomers, and the like.

Different configurations are possible depending on the kind of force applied. As discussed above, FIG. 2 depicts typical force characteristics for frictional contact. The force characteristic has a velocity weakening effect for relative velocities that are not close to zero. As discussed above, harmonic or periodic relative movement between two elements will cause energy to be input into the system. Furthermore, as described above, in this case, damping is only effective when the relative movement of the interacting surfaces approaches zero (e.g., point 204 in fig. 2). An alternative (or in combination with a friction damper) may be a viscous damper.

Turning now to fig. 29, various torque (T)/force (F) characteristics of a viscous fluid are illustratively shown relative to relative displacement between two parts connected by a connecting force

Graph 2900 of (e.g., relative movement/velocity). In this graph, curve 2902 represents the properties of a Newtonian fluid, curve 2904 represents the properties of a shear-thinning non-Newtonian fluid, and curve 2906 represents the properties of a shear-thickening non-Newtonian fluid. Although graph 2900 is illustrative of a fluid, such principles may be applicable to other types of dampers, such as non-contact damping (e.g., eddy current damping). On the graph 2900, the curve 2902 includes

points

1, 2, 3, the curve 2904 includes

points

4, 5, 6, and the curve 2906 includes

points

7, 8, 9. Points 1-9 represent torque T or force F versus relative displacement

The difference relationship of (a).

In graph 2900, the slopes of

curves

2902, 2904, 2906 (e.g., at points 1-9) are positive, and relative movement with respect to these points (including average velocity at that point)

And relative displacement, velocity or acceleration fluctuations relative to the forcibly connected parts caused by periodic superimposed oscillations (e.g. caused by HFTO) will provide damping to the system. The relative movement may for example occur between a part connected to the borehole wall, for example by viscous friction in the tangential direction, as is present with a non-rotating sleeve or a steering unit. Two interacting bodies positively connected by this property will also provide damping to HFTO if a positive average rotational speed is applied. Disadvantageously, this characteristic will also result in an average static force (T, F in fig. 26 and corresponding to points 1-9) from the contact surface that reduces the power from the rotation available for rock destruction. That is, the damper acts as a brake for rotation of the downhole system. Thus, in such cases, higher power may be required at the surface rotation system, which drives the cutting action at the drill bit.

The damping required depends linearly on the differenceThe slope of the torque versus relative displacement curve, which may be designated as the viscous damping coefficient d (d) in FIG. 29₁-d₉) And increases quadratically with mass normalized mode shape amplitude (e.g., as shown in fig. 9B). The static dissipated energy from a constant relative movement also increases linearly with the viscous damping coefficient d. Since the mode-mode amplitude is very localized and very high at the drill bit and therefore the relative movement between the two positively connected surfaces is high as described above, the static energy dissipation is also high and the damping is effective. Due to the localization and high mode-shape amplitude, the length of the damper can be relatively short (e.g., axial). The braking force of the relatively short damper is smaller than that of the relatively long damper. Thus, the trade-off between dynamically provided damping (e.g. to mitigate HFTO) and (unwanted) static energy dissipation is particularly good near, at or in the drill bit.

Furthermore, in some embodiments, magnetic damping may be employed. Magnetic damping may be achieved by permanent magnets (e.g., mounted on an inertia ring or mass element) that allow movement relative to the coil and that can be used to damp the HFTO. According to magnetic principles, the damping force characteristics are similar to hydraulic (e.g., eddy) or frictional (hysteresis) forces. In some such configurations, the force will act in the direction of tangential acceleration or any other direction that can cause damping to occur in the torsional direction or the direction that should be damped.

Furthermore, in some embodiments, piezoelectric damping principles may be employed to prevent HFTO from occurring at the drill bit. Piezoelectric material connected to an inertia ring or tangential mass on one side and to the drill bit on the other side may be used. The electrodes of the piezoelectric material may be connected to a circuit incorporating coils, resistors and capacitive or semi-active or active components. A combination of electrical components may be used to achieve advantageous damping characteristics between the inertia ring and the bit components. The circuit may be tuned to the natural frequency of the system to act as a tuned mass damper (i.e., for one or more desired modes). The resistor may be arranged to dissipate energy directly if the piezoelectric stack is deformed by the relative force between the mass element and the drill bit member. In addition, of piezoelectric material and inertial ring massThe stiffness may also be tuned to a specific frequency. The electrodes of the piezoelectric material may be arranged to damp the torsional vibrations. The direction of the damping force can be different from the direction of the electrodes using the advantageous conversion effect from mechanical force to electrical signal proposed by the design of the piezoelectric actuator. The well-known piezoelectric coefficient effect is D₃₃(in the direction of the force), D₃₁(orthogonal to the direction of the force) and D₁₅(shear stress). The arrangement of piezoelectric material can be placed to optimize or control the coupling between the mechanical and electrical systems for a particular mode or modes critical to HFTO. Further, a variety of different materials that transmit mechanical forces or stresses or related loads into electrical signals may be used without departing from the scope of the present disclosure.

In addition, internal damping and the resulting material forces can be used to reduce HFTO. That is, material damping can be achieved passively through the damping properties of high damping materials. Some such materials may include, but are not limited to, polymers, elastomers, rubbers, etc., as well as the damping effect of multi-functional materials such as shape memory alloys. The material properties of some materials, such as shape memory alloys, can be actively influenced or controlled to achieve a greater damping effect.

Other damping configurations are possible without departing from the scope of the present disclosure. For example, negative capacitance and semi-active components using switching techniques may be employed. Additional damping techniques and components may be used, and the above-described embodiments and variations are provided for purposes of illustration and explanation and are not intended to be limiting. All damping principles described herein can be adjusted to act as tuned mass dampers by adding mechanical springs tuned to specific frequencies and by adding any type of damping. Further, one or more of the damping principles (or other methods/mechanisms) described herein may be combined in a multi-principle configuration. For example, the ring type inertial dampers may be combined with tangential mass inertial dampers mounted within or attached to the blades of the fracturing apparatus. Furthermore, magnetic damping forces, hydraulic damping forces, frictional damping forces, piezoelectric damping forces and material damping forces and principles may be combined to achieve a robust damping effect such as e.g. with respect to temperature.

As described above, one or more damper elements may be integrated into a drill bit or other fracturing device. For example, a ring type bit damper may be positioned in or around the bit shank. In some configurations, the damper inertia ring may be lubricated with mud or covered by a sleeve design. In some configurations, a closed or uninterrupted loop may be employed. In other configurations, the partial arcs may be assembled around the bit shank (e.g., may be installed in situations where the ring cannot be otherwise assembled). In some such embodiments, two half-ring arcs may be employed. In other embodiments, more than two ring arcs may be used to form a full hoop (circumferential) structure or less than a full hoop (circumferential) structure, depending on the particular configuration implemented.

In some embodiments, a broken ring configuration may be employed in which discrete masses are disposed behind or adjacent to blades of a drill bit. In another example, the complete ring structure may be disposed adjacent to the blades, but specific additional mass elements or features of the ring may be positioned relative to specific blades of the drill bit. One such example may have a relatively thick ring and a lower thickness at the location of the insert to allow the chip flow to pass along the drill bit.

In some embodiments, a limit stop may be provided for the ring-type damper element, and may prevent the ring from moving freely around the circumference of the drill bit. Such limit stops may be provided in embodiments where the mass or higher is located behind or adjacent to a particular blade. In such cases, the limit stops may ensure that the mass or added mass remains in a certain position relative to the blade.

It should be understood that the friction-type damper elements of the present disclosure may employ radial and/or axial friction. The radial friction force can be realized by a spring or by an elastic design of an inertia ring with two half shells and is prestressed. The axial normal force may be achieved by a spring, the weight of the mass/inertia in the vertical bore and/or the spring may be built up from a housing, etc. The material of the drill bit or other fracturing device may be steel or matrix composite, etc. In some embodiments, bearings may be used in the radial direction to ensure movement of the inertia ring. That is, bearings may be provided to ensure circumferential and/or tangential movement of the damper element. The axial bearing may be used to decouple the potential normal force spring stack from rotational movement.

In some embodiments, the tangential damper element may alternatively be implemented in or on the blade of the fracturing device, from or in combination with a ring-type damper element. In some such embodiments, the tangential damper element may be mounted within a housing that is threaded into the blade. In some such configurations, one or more limit stops may be provided to prevent the tangential damper from sticking or wedging into edges or corners of the housing. A spring or other biasing element or structure may be used to achieve a limit of contact between the stop and the mass of the tangential damper. In some embodiments, the spring rate or gap in the housing may be selected to allow the mass of the tangential damper to move within the housing and thus enable damping of vibrations, as described above.

Adjustment elements that change the nature of the contact between contact elements in the drill bit may also be employed. For example, the normal force may be adjusted in frictional contact. Furthermore, the efficiency of the damping device may be measured by load and acceleration or other vibration measurement sensing devices.

Accordingly, embodiments of the present disclosure relate to positioning a damping system, such as a ring-type damper or a tangential damper, at or in a drill bit or other fracturing device of a downhole system. By positioning the damping system at or in the drill bit, improved damping of HFTO or other vibrational modes can be achieved.

Embodiment 1: a system for damping torsional oscillations of a downhole system, the system comprising: a downhole string comprising a fracturing device; and a damping system located at least one of: in and/or on the downhole tubular string, the damping system is configured to damp torsional oscillations of the downhole tubular string.

Embodiment 2: a system according to any preceding embodiment, wherein the damping system is arranged to provide viscous damping.

Embodiment 3: a system according to any preceding embodiment, wherein the damping system is arranged to provide piezoelectric damping.

Embodiment 4: a system according to any preceding embodiment, wherein the damping system is arranged to provide eddy current damping.

Embodiment 5: a system according to any preceding embodiment, wherein the damping system comprises at least one damper element arranged to be in contact with a portion of the comminution apparatus.

Embodiment 6: the system according to any preceding embodiment, wherein the damper element is configured to move relative to the fragmenting device at a velocity that is a sum of a periodic velocity fluctuation having an amplitude and an average velocity.

Embodiment 7: the system of any preceding embodiment, wherein the fracturing device is a drill bit comprising a bit body and a bit shank.

Embodiment 8: a system according to any preceding embodiment, wherein at least one damper element is arranged around the drill bit shank.

Embodiment 9: the system of any preceding embodiment, wherein: the at least one damper element is a ring-type structure disposed circumferentially around the bit shank, the bit body includes a plurality of blades, and the ring-type structure includes one or more mass structures, wherein at least one mass structure is disposed relative to one of the plurality of blades.

Embodiment 10: the system according to any preceding embodiment, wherein the at least one damper element comprises: a first element arranged to be in contact with the drill bit shank; a second element disposed outside the first element; and a third element disposed outside the second element.

Embodiment 11: the system according to any preceding embodiment, wherein the first element is an axial wave spring, the second element is a radial friction surface housing, and the third element is an inertia bar housing.

Embodiment 12: the system of any preceding embodiment, further comprising: a cap sleeve disposed around the at least one damper element disposed around the drill bit shank, the cap sleeve configured to protect the at least one damper element disposed around the drill bit shank.

Embodiment 13: the system according to any preceding embodiment, wherein the fracturing apparatus comprises at least one blade, wherein at least one dampener element is disposed in the at least one blade.

Embodiment 14: the system according to any preceding embodiment, wherein the at least one damper element is a tangential damper element.

Embodiment 15: the system according to any preceding embodiment, wherein the at least one damper element comprises: a housing configured to fit within the at least one blade; and a mass element disposed within the housing and movable within the housing.

Embodiment 16: the system of any preceding embodiment, wherein the at least one damper element further comprises: a mounting element located within the housing; and a contact element located within the housing, wherein the mass element is disposed between the mounting element and the contact element, and wherein the mounting element is configured to urge the mass element towards the contact element within the housing.

Embodiment 17: the system of any preceding embodiment, wherein the at least one damper element further comprises: a limit stop disposed within the housing and configured to prevent the mass element from sticking within the housing.

Embodiment 18: a method of damping torsional oscillations of a downhole system in a borehole, the method comprising: installing a damping system at least one of: on and/or in a downhole system comprising a downhole string having a fracturing device, and the damping system is configured to damp torsional oscillations of the downhole string.

Embodiment 19: a method according to any preceding embodiment, wherein the damping system comprises at least one damper element arranged to be in contact with a portion of the comminution apparatus.

Embodiment 20: the method according to any preceding embodiment, wherein the damper element moves relative to the fragmenting device at a velocity that is the sum of a periodic velocity fluctuation having an amplitude and an average velocity, wherein the average velocity is lower than the amplitude of the periodic velocity fluctuation.

Embodiment 21: a method according to any preceding embodiment, wherein the damping system is arranged to provide at least one of viscous damping, frictional damping, hydraulic damping, piezoelectric damping, eddy current damping and magnetic damping of torsional oscillations of the downhole tubular string.

In support of the teachings herein, various analysis components may be used, including digital systems and/or analog systems. For example, a controller, computer processing system, and/or geosteering system as provided herein and/or used with embodiments described herein may include a digital system and/or a simulated system. These systems may have components such as processors, storage media, memories, inputs, outputs, communication links (e.g., wired, wireless, optical, or otherwise), user interfaces, software programs, signal processors (e.g., digital or analog), and other such components (such as resistors, capacitors, inductors, and the like) for providing the operation and analysis of the apparatus and methods disclosed herein in any of several ways that are well known in the art. It is contemplated that these teachings may be implemented, but are not necessarily, in combination with a set of computer-executable instructions stored on a non-transitory computer-readable medium including a memory (e.g., ROM, RAM), an optical medium (e.g., CD-ROM), or a magnetic medium (e.g., diskette, hard drive), or any other type of medium, that when executed, cause a computer to implement the methods and/or processes described herein. In addition to the functions described in this disclosure, these instructions may provide equipment operation, control, data collection, analysis, and other functions that a system designer, owner, user, or other such person deems relevant. The processed data (such as the results of the implemented method) may be transmitted as a signal via the processor output interface to the signal receiving device. The signal receiving device may be a display monitor or a printer for presenting the results to a user. Alternatively or in addition, the signal receiving device may be a memory or a storage medium. It should be understood that storing the results in a memory or storage medium may transition the memory or storage medium from a previous state (i.e., containing no results) to a new state (i.e., containing results). Further, in some embodiments, an alert signal may be transmitted from the processor to the user interface if the result exceeds a threshold.

In addition, various other components may be included and required to provide aspects of the teachings herein. For example, sensors, transmitters, receivers, transceivers, antennas, controllers, optical units, electrical units, and/or electromechanical units may be included to support the various aspects discussed herein or to support other functionality beyond the present disclosure.

The use of the terms "a" and "an" and "the" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Further, it should be noted that the terms "first," "second," and the like, herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. The modifier "about" used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes the degree of error associated with measurement of the particular quantity).

It should be appreciated that various components or techniques may provide certain necessary or beneficial functions or features. Accordingly, such functions and features as may be needed in support of the appended claims and variations thereof are considered to be inherently included as part of the teachings herein and as part of the present disclosure.

The teachings of the present disclosure may be used in a variety of well operations. These operations may involve treating the formation, fluids residing in the formation, the borehole, and/or equipment in the borehole, such as production tubing, with one or more treating agents. The treatment agent may be in the form of a liquid, a gas, a solid, a semi-solid, and mixtures thereof. Exemplary treatment agents include, but are not limited to, fracturing fluids, acids, steam, water, brines, corrosion inhibitors, cements, permeability modifiers, drilling muds, emulsifiers, demulsifiers, tracers, mobility improvers, and the like. Exemplary well operations include, but are not limited to, hydraulic fracturing, stimulation, tracer injection, cleaning, acidizing, steam injection, water injection, cementing, and the like.

While the embodiments described herein have been described with reference to various embodiments, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular instrument, situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out the described features, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Accordingly, the embodiments of the present disclosure should not be viewed as limited by the foregoing description, but rather should be limited only by the scope of the appended claims.

Claims

1. A system (712) for damping torsional oscillations of a downhole system, the system (712) comprising:

a downhole string (704) comprising a fracturing apparatus (2300); and

a damping system (1000) located at least one of: in and/or on the tubular string (704), the damping system (1000) is configured to damp torsional oscillations of the tubular string (704).

2. The system (712) of claim 1, wherein the damping system (1000) is arranged to provide at least one of viscous damping, piezoelectric damping, eddy current damping.

3. The system (712) according to any preceding claim, wherein the damping system (1000) comprises at least one damper element (2304) arranged in contact with a portion of the fracturing device (2300).

4. The system (712) of claim 3, wherein the damper element (2304) is configured to move relative to the fracturing device (2300) at a velocity that is a sum of a periodic velocity fluctuation having an amplitude and an average velocity.

5. The system (712) according to any preceding claim, wherein the fracturing device (2300) is a drill bit (2402) comprising a bit body (2406) and a bit shank (2410).

6. The system (712) of claim 5, wherein at least one damper element (2304) is disposed about the bit shank (2410), preferably the system further comprising: a cover sleeve (2418) disposed about the at least one damper element (2304) disposed about the bit shank (2410), the cover sleeve (2418) configured to protect the at least one damper element (2304) disposed about the bit shank (2410).

7. The system (712) of claim 5, wherein:

the at least one damper element (2304) is a ring-type structure disposed circumferentially about the bit shank (2410),

the bit body (2406) includes a plurality of blades (2302), and

the ring-type structure includes one or more mass structures (2506), wherein at least one mass structure is disposed relative to one of the plurality of blades (2302).

8. The system (712) of claim 5, wherein the at least one damper element (2304) includes:

a first element (1010) arranged to be in contact with the bit shank (2410);

a second element (1012) disposed outside of the first element (1010); and

a third element (2416) disposed outside of the second element (1012),

preferably, wherein the first element (1010) is an axial wave spring, the second element (1012) is a radial friction surface housing, and the third element (2416) is an inertia stem (2410) housing.

9. The system (712) according to any preceding claim, wherein the fracturing apparatus (2300) comprises at least one blade (2302), wherein at least one damper element (2304) is disposed in the at least one blade (2302).

10. The system (712) of claim 9, wherein the at least one damper element (2304) is one of: is a tangential damper element (2304) or comprises a housing (2702) configured to fit within the at least one blade (2302) and a mass element (2704) disposed within the housing (2702) and movable therein.

11. The system (712) of claim 10, wherein the at least one damper element (2304) further comprises:

a mounting element (2706) located within the housing (2702); and

a contact element (2708) located within the housing (2702),

wherein the mass element (2704) is arranged between the mounting element (2706) and the contact element (2708), and wherein the mounting element (2706) is configured to press the mass element (2704) towards the contact element (2708) within the housing (2702).

12. The system (712) of claim 11, wherein the at least one damper element (2304) further comprises a limit stop disposed within the housing (2702) and configured to prevent the mass element (2704) from sticking within the housing (2702).

13. A method of damping torsional oscillations of a downhole system (1002) in a borehole (26), the method comprising:

installing a damping system (1000) at least one of: on and/or in the downhole system (1002), the downhole system (1002) comprising a downhole string (704) with a fracturing device (2300), and the damping system (1000) being configured to damp torsional oscillations of the downhole string (704).

14. The method of claim 13, wherein the damper element (2304) moves relative to the fracturing device (2300) at a velocity that is a sum of a periodic velocity fluctuation having an amplitude and an average velocity, wherein the average velocity is lower than the amplitude of the periodic velocity fluctuation.

15. The method of any of claims 13 to 14, wherein the damping system (1000) is arranged to provide at least one of viscous damping, frictional damping, hydraulic damping, piezoelectric damping, eddy current damping, and magnetic damping of torsional oscillations of the downhole tubular string (704).