CN111456716A - Underground strain distribution monitoring system and method based on distributed optical fiber sensing - Google Patents
Underground strain distribution monitoring system and method based on distributed optical fiber sensing Download PDFInfo
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Abstract
The invention provides a distributed optical fiber sensing-based downhole strain distribution monitoring system and a monitoring method thereof, which bind an armored optical cable at the outer side of a casing of a vertical well, an inclined well or a horizontal well and permanently fix the armored optical cable by using well cement, bind the armored optical cable at the outer side of a continuous oil pipe by using a metal clip and fix the armored optical cable, construct a long-term strain monitoring sensing unit for an oil and gas production well, a water injection well and a monitoring or observation well, and jointly form a distributed strain sensing and distributed temperature sensing (DSS/DTS) composite modulation and demodulation instrument near a well mouth to form the distributed optical fiber sensing-based downhole strain distribution change dynamic monitoring system and the monitoring method, thereby effectively ensuring the oil and gas production well, the long-term stable, safe and reliable operation of water injection wells and monitoring or observation wells provides indispensable means, systems and methods for scientific management of oil and gas reservoirs and enhanced recovery efficiency.
Description
Technical Field
The invention belongs to the technical field of strain measurement, and particularly relates to a distributed optical fiber sensing-based underground strain distribution monitoring system and method.
Background
The optical fiber sensing technology started in 1977 and developed rapidly along with the development of the optical fiber communication technology, and the optical fiber sensing technology is an important mark for measuring the informatization degree of a country. The optical fiber sensing technology is widely applied to the fields of military affairs, national defense, aerospace, industrial and mining enterprises, energy environmental protection, industrial control, medicine and health, metering test, building, household appliances and the like, and has a wide market. There are hundreds of fiber sensing technologies in the world, and physical quantities such as temperature, pressure, flow, displacement, vibration, rotation, bending, liquid level, speed, acceleration, sound field, current, voltage, magnetic field, radiation and the like realize sensing with different performances.
The downhole optical fiber sensing system can be used downhole to make measurements of stress, strain, pressure, temperature, noise, vibration, acoustic, seismic, flow, compositional analysis, electric and magnetic fields. The system is based on a full armored optical cable structure, and the sensor and the connecting and data transmission cable are all made of optical fibers. At present, there are various underground armored optical cables, such as those placed in an underground control pipeline, placed in a coiled tubing, directly integrated into the wall of the coiled tubing made of composite material, bound and fixed outside the coiled tubing, placed in a casing, bound and fixed outside the casing and permanently fixed with well-cementing cement.
The strain measurement is a basic task in the mechanical property test of materials and structures, is the basis for knowing the deformation, damage and failure behaviors of the materials under the action of factors such as mechanical load and the like, and has important values for determining structure design allowable values, structure life prediction and evaluation and the like. The strain measurement method mainly comprises the following steps: electrical measurements, optical measurements, acoustic emissions, brittle coating methods, strain mechanics measurements, and the like. Among them, the electrical measurement and the optical measurement are most widely used.
The electrical measurement method is a measurement method for converting a non-electrical quantity of strain into an electrical quantity by means of an electronic instrument. It can be used for on-site measurement and analog measurement. The electrical measurement method is widely applied to a resistance strain test method, and the basic principle is an experimental stress analysis method for determining the surface stress state of a member according to a strain-stress relationship by using a resistance strain gauge to measure the linear strain of the surface of the member. The method is that the resistance value of the resistance strain gauge changes correspondingly when the member deforms, then the resistance strain gauge converts the resistance change into the change of voltage (or current), and then the change is converted into the strain value or the signal of the voltage (or current) proportional to the strain value is output, and the measured strain or stress can be obtained by recording the signal by the recorder. The traditional strain measurement method mostly adopts a resistance-type strain gauge, but the strain gauge is single-point measurement and a large number of wires are needed to connect the strain gauge in practical use.
The optical measurement is a measurement method for researching mechanical quantities such as stress, strain and displacement in a structure by an experimental means by applying an optical principle. The optical measurement method includes photoelasticity, holographic interference, laser speckle interference, moire method, and the like. The optical fiber strain measurement method uses an optical fiber as a sensing medium, and utilizes an optical principle and technology to detect and measure the change of optical parameters such as light intensity, phase, polarization state, wavelength and the like caused by the action of external factors (such as tension, pressure and the like) so as to realize the measurement of the strain quantity of a measured object.
With the development of optical technology, quasi-distributed fiber sensors represented by Fiber Bragg Grating (FBG) sensors and the like have appeared, however, the measuring point of the fiber bragg grating sensor is limited by the laser bandwidth. Nowadays, distributed optical fiber sensing technology is mature day by day, and distributed optical fiber sensors based on back rayleigh scattering have good precision, linearity and repeatability in the aspect of strain measurement, and can already have the potential of replacing traditional resistance-type strain gauges and optical fiber bragg grating sensors in various fields. The distributed optical fiber sensor has the characteristics of extremely high measuring point density, controllable spacing, small mass, corrosion resistance, electric insulation, high precision and good repeatability. In addition, it has better adaptability to the shape of the structure surface based on its soft and tough nature.
The strain (deformation) generated by underground rock or rock stratum caused by underground stress concentration or overlarge area can cause the deformation or damage of a downhole casing and the deformation or damage of a coiled tubing in the downhole casing, and even the casing and/or the coiled tubing are twisted off and a drilled hole is abandoned when the strain (deformation) is serious. There is a need for long term and real time monitoring of strain caused by downhole earth stresses. Due to the high temperature, high pressure and narrow space in the well, conventional electrical measurement, acoustic emission, brittle coating, strain mechanical measurement, etc. are not suitable for strain measurement in the downhole environment. Due to the popularization and application of the underground high-temperature-resistant and high-pressure-resistant armored optical cable, a good foundation is provided for underground strain measurement by applying a photometric method. Although quasi-distributed fiber sensors represented by Fiber Bragg Grating (FBG) sensors and the like can be used for strain measurement and real-time long-term monitoring of underground environments, measuring points of the fiber bragg grating sensors are limited by laser bandwidth and are not suitable for multi-point strain measurement and real-time monitoring with high density or high spatial resolution in deep wells and ultra-long horizontal wells.
Disclosure of Invention
The invention provides a long-term comprehensive monitoring system for underground strain distribution change based on distributed optical fiber sensing, which is formed by binding an armored optical cable on the outer side of a sleeve of a vertical well, an inclined well or a horizontal well by using a metal clamp and permanently fixing the armored optical cable by using well cement, constructing a sensing and signal transmission unit (module) of a long-term real-time monitoring and measuring system for underground stratum strain distribution change based on distributed optical fiber sensing, and connecting a distributed optical fiber strain sensing (DSS) and distributed optical fiber temperature sensing (DTS) composite modulation and demodulation instrument on the ground of a wellhead with the armored optical cable near the wellhead.
The invention aims to overcome the defects of the existing underground strain measurement technology, provides a long-term real-time monitoring and measuring system for underground stratum strain distribution change based on distributed optical fiber sensing, which is formed by binding an armored optical cable at the outer side of a casing of a vertical well, an inclined well or a horizontal well and permanently fixing the armored optical cable by using well cementation cement, monitors and measures underground stress possibly causing damage or damage to the underground casing and various underground tools and pipelines in a long-term real-time manner, and provides indispensable means, systems and methods for ensuring long-term stable, safe and reliable work of an oil and gas production well, a water injection well and a monitoring or observation well.
In order to achieve the purpose, the specific technical scheme of the invention is as follows:
The underground strain distribution monitoring system based on distributed optical fiber sensing comprises a metal sleeve, wherein a coiled tubing is arranged in the metal sleeve, a first armored optical cable is fixed on the outer side of the metal sleeve, and a second armored optical cable is fixed on the outer side of the coiled tubing;
The DSS/DTS composite modulation and demodulation instrument is placed near a wellhead and comprises data acquisition and modulation and demodulation functions of distributed strain sensing and distributed temperature sensing; the DSS/DTS composite modulation and demodulation instrument is respectively connected with the first armored cable and the second armored cable.
Furthermore, the first armored optical cable and the second armored optical cable are armored optical cables, each armored optical cable comprises an optical fiber, each optical fiber is a single-mode or multi-mode or special strain sensitive optical fiber, an inner continuous metal thin tube and an outer continuous metal thin tube are sequentially arranged outside each optical fiber to encapsulate the optical fiber, and the inner continuous metal thin tube and the outer continuous metal thin tube are made of stainless steel or alloy metal; and single-layer or multi-layer armored steel wires can be added outside the outer continuous metal thin tube according to needs to protect the armored optical cable from being damaged or extruded and broken in the process of being installed in a well along with the sleeve or the oil pipe.
Furthermore, a plurality of optical fibers and high-temperature-resistant optical fiber paste are placed in the inner continuous metal thin tube, and in addition, before the inner continuous metal thin tube is welded by laser, the inner wall of the inner continuous metal thin tube is fixed together with the continuous optical fibers by using high-temperature-resistant epoxy resin at equal intervals (between 10 meters and 100 meters), so that the optical fibers in the armored optical cable can detect the strain produced after underground ground stress acts on the metal sleeve and the armored optical cable timely and sensitively.
The inner continuous metal thin tube can also be internally provided with a high-sensitivity strain special optical fiber which is tightly wrapped by a high-temperature-resistant high-strength composite material or wrapped by an injection molding machine in a one-step forming way, and the high-sensitivity strain special optical fiber is tightly attached to the inner continuous metal thin tube and sealed in the continuous metal thin tube so as to enhance the tensile, anti-extrusion and anti-impact capabilities of the armored optical cable.
The metal sleeves are connected in sequence and further comprise first annular metal clips, and the first annular metal clips are fixedly arranged at the positions of the metal sleeve shoes. The coiled tubing oil pipe is characterized by further comprising second annular metal clips, wherein the second annular metal clips are installed and fixed on the outer side of the coiled tubing at equal intervals.
In strain/temperature measurements using distributed fiber optic sensors, back rayleigh scattering is measured using wavelength-scanning interferometry as a function of position on the fiber. The rayleigh scattering in an optical fiber occurs due to refractive index fluctuations in the length direction of the fiber. Although the scattering is random, for a given fiber, if the state of the fiber does not change, the same wavelength of reflected light is always generated, and this characteristic is called the inherent texture information of the fiber. If a certain position of the optical fiber is deformed due to the influence of load or temperature, only the wavelength of the reflected light at the position is deviated, and by comparing the reflected light before and after the deformation, it is possible to confirm at which position of the optical fiber the deformation occurs. Under normal conditions, the spectrum of the scattered light in the fiber shifts primarily due to strain or temperature changes. The spectral drift obtained from the strain or temperature t response is similar to the drift of resonance wave Δ λ or the spectral drift of bragg grating Δ ν, namely:
Δλ/λ＝-Δυ/υ＝KTΔt+K
In the formula: λ and υ are average light wavelength and frequency, respectively; k TAnd K Temperature and strain standard constants, respectively, for most germanosilicate core fibers, KT＝6.45μ℃-1，K＝0.78。
the Gauge L ength (Gauge L ength) of the distributed optical fiber sensor is adjustable, but the Gauge L ength can affect the spectral resolution and the signal-to-noise ratio of a measurement signal.
The monitoring method of the underground strain distribution monitoring system based on the distributed optical fiber sensing comprises the following steps:
(a) Synchronously and slowly putting the metal sleeve and the first armored optical cable into the drilled well hole;
(b) The first annular metal clip is arranged at the joint of the two metal sleeves at the wellhead to fix and protect the first armored cable from moving and/or being damaged in the process of casing running;
(c) Pumping cement slurry from the well bottom by using a high-pressure pump truck after the casing is laid, so that the cement slurry returns to the well head from the well bottom along an annular area between the outer wall of the metal casing and the drill hole, and permanently fixing the metal casing, the first armored optical cable and the stratum rock together after the cement slurry is solidified;
(d) Synchronously and slowly putting the continuous oil pipe and the second armored optical cable underground into a metal cased well for well cementation and completion;
(e) The second annular metal clip is arranged on the coiled tubing at a wellhead at the same interval (about 10 meters), so that the second armored optical cable is fixed and protected from being damaged in the installation process of the lower coiled tubing, and the armored optical cable and the coiled tubing have good adherence strain coupling;
(f) Connecting the single-mode optical fiber or the special strain sensitive optical fiber in the first armored optical cable to a DSS signal input end of a DSS/DTS composite modulation and demodulation instrument at a wellhead, and connecting the single multimode optical fiber or the two multimode optical fibers in the first armored optical cable to a DTS signal input end of the DSS/DTS composite modulation and demodulation instrument;
(g) Connecting the single-mode optical fiber or the special strain sensitive optical fiber in the second armored optical cable to a DSS signal input end of a DSS/DTS composite modulation and demodulation instrument at a wellhead, and connecting the single multimode optical fiber or the two multimode optical fibers in the second armored optical cable to a DTS signal input end of the DSS/DTS composite modulation and demodulation instrument;
(h) Continuously monitoring and measuring DSS and DTS signals in a first armored optical cable outside the metal sleeve and a second armored optical cable outside the coiled tubing through a DSS/DTS composite modulation and demodulation instrument placed beside a wellhead during long-term underground strain monitoring and measuring;
(i) Modulating and demodulating DSS signals and DTS signals which are continuously measured by a DSS/DTS composite modulation and demodulation instrument, converting DSS data into strain which is generated by underground ground stress acting on the metal sleeve and the first armored cable and strain which is generated by underground ground stress acting on the coiled tubing and the second armored cable, and converting DTS data into distribution data of temperature change outside the underground metal sleeve and the coiled tubing;
(j) According to the temperature data outside the underground metal casing and the temperature data outside the continuous oil casing which are monitored and measured, a formula delta lambda/lambda-delta upsilon/upsilon-K is utilized TΔt+KCorrecting DSS measured data by using temperature value of a specific measurement position to perform scattered light spectrum drift in the optical fiber caused by temperature change, and obtaining a true strain value of the outer wall of the metal sleeve and the outer wall of the continuous oil pipe, wherein the temperature influence is eliminated;
(k) Calculating the differential of the strain quantities of the outer wall of the metal sleeve and the outer wall of the coiled tubing, which are monitored and measured in real time for a long time, to the time to obtain the change rate of the strain quantities along with the time;
(l) And analyzing the strain and strain rate (strain change rate along with time) of the outer wall of the metal sleeve and the outer wall of the coiled tubing, which are monitored and measured in real time for a long time, and timely giving out early warning or alarming when the strain and strain rate of the metal sleeve and the coiled tubing exceed threshold values and possibly cause deformation damage of the metal sleeve and the coiled tubing according to the strain and strain rate threshold value standards of the metal sleeve and the coiled tubing set in underground engineering, so that the long-term stable, safe and reliable work of an oil-gas production well, a water injection well and a monitoring or observation well is ensured.
The optical fiber strain measurement method uses an optical fiber as a sensing medium, and utilizes an optical principle and technology to detect and measure the change of optical parameters such as light intensity, phase, polarization state, wavelength and the like caused by the action of external factors (such as tension, pressure and the like) so as to realize the measurement of the strain quantity of a measured object.
The distributed Optical fiber strain detection technology based on Brillouin Optical Time Domain Reflection (BOTDR) has the advantages of single-ended input, long measurement distance, measurable breakpoint, full-distributed detection and the like, and can be effectively applied to structural health state monitoring of large-scale basic engineering. The strain detector based on the BOTDR combines a coherent detection method and a microwave heterodyne frequency sweeping method to realize Brillouin scattering signal detection, and by utilizing the advantage of FPGA high-speed operation, the noise reduction of the Brillouin scattering signal and the demodulation of a Brillouin gain spectrum are realized so as to improve the real-time performance of strain detection. The strain and strain rate of the underground casing and the coiled tubing in the casing can be monitored or detected for a long time, and the long-term stable, safe and reliable work of an oil-gas production well, a water injection well and a monitoring or observation well can be effectively guaranteed in a mode of early warning or alarming.
the distributed optical fiber temperature measurement system (DTS) is used for measuring the temperature profile in a shaft in real time, and the principle of the DTS is that Raman (Raman) scattering and Optical Time Domain Reflection (OTDR) principles generated when light is transmitted in an optical fiber are used for obtaining space temperature distribution information, after a high-power narrow pulse width laser pulse L D is incident on a sensing optical fiber, weak back scattering light is generated, and Rayleigh (Rayleigh), Anti-Stokes (Anti-Stokes) and Stokes (Stokes) light respectively exist according to different wavelengths.
The underground strain distribution monitoring system based on distributed optical fiber sensing and the monitoring method thereof provided by the invention are a dynamic monitoring method and technology for underground strain distribution change with low cost, high precision and high reliability. The invention provides a method, a system and a method for binding metal clips for armored cables on the outer side of a casing of a vertical well, an inclined well or a horizontal well and permanently fixing the same by using well cementation cement, binding metal clips for armored cables on the outer side of a continuous oil pipe and fixing the same, constructing a long-term strain monitoring sensing unit (module) for an oil and gas production well, a water injection well and a monitoring or observation well, and forming a distributed strain sensing and distributed temperature sensing (DSS/DTS) composite modulation and demodulation instrument near a well head together to form a dynamic monitoring system for underground strain distribution change based on distributed optical fiber sensing, effectively ensuring long-term stable, safe and reliable work of the oil and gas production well, the water injection well and the monitoring or observation well, and providing indispensable means, systems and methods for scientific management and improvement of recovery ratio of oil and gas reservoirs.
Drawings
FIG. 1 is a schematic diagram of the system architecture of the present invention.
FIG. 2 is a schematic view of a downhole metallic casing and armored cable configuration of the present invention.
Fig. 3 is a schematic view of the internal structure of the armored fiber optic cable of the present invention.
Detailed Description
The embodiments of the present invention will be described in detail with reference to the accompanying drawings, which are not intended to limit the present invention, but are merely exemplary, and the advantages of the present invention will be more clearly understood and appreciated by way of illustration.
The invention discloses a specific implementation mode of a downhole strain distribution monitoring system based on distributed optical fiber sensing, which comprises the following steps:
As shown in fig. 1, the downhole strain distribution monitoring system based on distributed optical fiber sensing comprises a metal casing 1, a coiled tubing 2 arranged in the metal casing 1, and a DSS/DTS composite modem instrument 3 arranged near a wellhead, wherein the DSS/DTS composite modem instrument 3 comprises data acquisition and modem functions of distributed strain sensing and distributed temperature sensing.
The cable protection device further comprises a first armored cable 4 permanently fixed on the outer side of the metal sleeve 1, a second armored cable 5 semi-permanently fixed on the outer side of the continuous oil pipe 2, a first annular metal clip 8 installed at the boot of the metal sleeve 1 and protecting the first armored cable 4, and a second annular metal clip 9 installed on the outer side of the continuous oil pipe 2 and protecting the second armored cable 5;
The first armored optical cable 4 is arranged on the outer wall of the metal sleeve 1; the second armored optical cable 5 is arranged on the outer wall of the coiled tubing 2;
The first armored optical cable 4 arranged on the outer wall of the metal sleeve 1 and the second armored optical cable 5 arranged on the outer wall of the coiled tubing 2 are connected with the DSS/DTS composite modulation and demodulation instrument 3 at a wellhead;
According to the underground strain distribution monitoring system based on distributed optical fiber sensing, optical fibers 21 and high-temperature-resistant optical fiber paste are placed in inner continuous metal thin tubes (22), the optical fibers 21 are a plurality of single-mode or multi-mode or special strain sensitive optical fibers, and in addition, before the inner continuous metal thin tubes (22) are subjected to laser welding, the optical fibers 21 and the inner walls of the inner continuous metal thin tubes (22) are fixed together by using high-temperature-resistant epoxy resin 24 at positions with equal intervals (between 10 meters and 100 meters), so that the optical fibers in first armored optical cables 4 and second armored optical cables 5 can timely and sensitively detect the strain produced after underground ground stress acts on metal sleeves 1 and continuous oil pipes 2 and on the first armored optical cables 4 and the second armored optical cables 5.
As shown in fig. 3, the first armored optical cable 4 and the second armored optical cable 5 both include optical fibers 21, and the optical fibers 21 are single-mode or multi-mode or special strain sensitive optical fibers; the optical fiber 21 is sequentially encapsulated by an inner continuous metal thin tube 22 and an outer continuous metal thin tube 23.
The inner continuous metal thin tube 22 can also be internally provided with a high-sensitivity strain special optical fiber 21 which is tightly wrapped by a high-temperature-resistant high-strength composite material or is manufactured by one-step forming and wrapping the optical fiber by an injection molding machine, and the high-sensitivity strain special optical fiber is tightly attached to the wall and sealed in the continuous metal thin tube 22 so as to enhance the tensile, anti-extrusion and anti-impact capabilities of the armored optical cable.
The first annular metal clip 8 is fixedly arranged at the boot of the metal sleeve 1 to protect the first armored cable 4 from moving and/or being damaged in the process of casing running.
The second annular metal clips 9 are installed and fixed on the outer side of the coiled tubing 2 at equal intervals, so that the second armored optical cable 5 is protected from being damaged in the installation process of the coiled tubing 2, and good strain signal coupling is achieved between the second armored optical cable 5 and the coiled tubing 2.
In order to adapt to the severe environment of underground high temperature and high pressure, most of the underground optical cables are armored by different materials and different structures, and the underground optical cables are high temperature resistant, high pressure resistant, stretch resistant, extrusion resistant and impact resistant, so that the integrity and smoothness of the underground optical cables during underground operation are ensured. One of the commonly used armoring techniques is to place one or several high temperature resistant single-mode or multi-mode or special strain sensitive optical fibers into a sealed fine stainless steel or alloy metal thin tube for protection. According to the magnitude of underground pressure and the external force strength in the underground operation process, sometimes one or more layers of stainless steel or alloy metal pipes with larger diameters are sleeved outside the fine stainless steel or alloy metal thin pipe provided with one or more high-temperature-resistant optical fibers, and even one or more layers of armored stainless steel wires are wound outside the layers of stainless steel or alloy metal pipes to enhance the tensile resistance, the extrusion resistance and the shock resistance of the armored optical cable.
The embodiment provides a distributed optical fiber sensing-based underground strain distribution monitoring system and a monitoring method thereof, which are a low-cost, high-precision and high-reliability dynamic monitoring method and technology for underground strain distribution change. The invention provides a method, a system and a method for binding an armored optical cable 4 at the outer side of a metal sleeve 1 of a vertical well, an inclined well or a horizontal well by using a metal clip 8 and permanently fixing the armored optical cable by using well cementation cement, and binding an armored optical cable 5 at the outer side of a continuous oil pipe 2 by using a metal clip 9 and fixing the armored optical cable, so as to construct a long-term strain monitoring sensing unit (module) for an oil and gas production well, a water injection well and a monitoring or observation well, and a DSS/DTS composite modulation demodulation instrument 3 near a well head to jointly form a dynamic monitoring system for underground strain distribution change based on distributed optical fiber sensing, thereby effectively ensuring long-term stable, safe and reliable work of the oil and gas production well, the water injection well and the monitoring or observation well, and providing indispensable means, systems and methods for.
A continuous metal casing 1 of several hundred to several thousand meters length is lowered downhole by continuously lowering several tens to several hundreds of metal casings 1 of about 10 meters in length into the wellbore. The bottom of each metal sleeve 1 with the length of about 10 meters is provided with a sleeve shoe with a slightly larger diameter for fixing the head and the tail of the two metal sleeve 1 sections together, and simultaneously, the phenomenon of eccentricity or misalignment of the upper and the lower metal sleeve 1 at the butt joint point is avoided. In order to protect the first armored cable 4 from being worn out during the operation of simultaneously lowering the metal casing 1 into the well or being crushed or broken at the position of the casing shoe, a first annular metal clip 8 is fixedly arranged at the position of each casing shoe for protecting the first armored cable 4 passing through the position of the casing shoe from moving and/or being damaged.
The first armored cable 4 is arranged outside the metal casing 1 of the vertical well, the inclined well or the horizontal well, and the metal casing 1 and the outside first armored cable 4 and the stratum are permanently fixed together by using cementing cement. When the coiled tubing 2 and the second armored optical cable 5 are synchronously and slowly put into the well of the metal casing 1 after well cementation and completion, the second annular metal clips 9 are installed on the coiled tubing 2 at the well head according to the same interval, so that the second armored optical cable 5 is fixed and protected from being damaged in the installation process of the coiled tubing 2, and the second armored optical cable 5 and the coiled tubing 2 have good strain signal coupling. The single-mode optical fiber or the special strain sensitive optical fiber in the first armored optical cable 4 and the second armored optical cable 5 is connected to the DSS signal input end of the DSS/DTS composite modulation and demodulation instrument 3 at a well head, and the single multimode optical fiber or the two multimode optical fibers in the first armored optical cable 4 and the second armored optical cable 5 are connected to the DTS signal input end of the DSS/DTS composite modulation and demodulation instrument 3 so as to carry out single-end input measurement or double-end input measurement.
In strain/temperature measurements using distributed fiber optic sensors, back rayleigh scattering is measured using wavelength-scanning interferometry as a function of position on the fiber. The rayleigh scattering in an optical fiber occurs due to refractive index fluctuations in the length direction of the fiber. Although the scattering is random, for a given fiber, if the state of the fiber does not change, the same wavelength of reflected light is always generated, and this characteristic is called the inherent texture information of the fiber. If a certain position of the optical fiber is deformed due to the influence of load or temperature, only the wavelength of the reflected light at the position is deviated, and by comparing the reflected light before and after the deformation, it is possible to confirm at which position of the optical fiber the deformation occurs. Under normal conditions, the spectrum of the scattered light in the fiber shifts primarily due to strain or temperature changes. The spectral drift obtained from the strain or temperature t response is similar to the drift of resonance wave Δ λ or the spectral drift of bragg grating Δ ν, namely:
Δλ/λ＝-Δυ/υ＝KTΔt+K
In the formula: λ and υ are average light wavelength and frequency, respectively; k TAnd K Temperature and strain standard constants, respectively, for most germanosilicate core fibers, K T＝6.45μ℃-1，K＝0.78。
the Gauge L ength (Gauge L ength) of the distributed optical fiber sensor is adjustable, but the Gauge L ength can affect the spectral resolution and the signal-to-noise ratio of a measurement signal.
The monitoring method of the underground strain distribution monitoring system based on the distributed optical fiber sensing comprises the following steps:
(1) Synchronously and slowly descending the metal sleeve 1 and the first armored optical cable 4 into a drilled well hole;
(2) The first annular metal clip 8 is arranged at the joint of the two metal sleeves 1 at the wellhead to fix and protect the first armored cable 4 from moving and/or being damaged in the casing running process;
(3) After the metal casing 1 is put down, pumping cement slurry from the well bottom by using a high-pressure pump truck, returning the cement slurry to the well head from the well bottom along an annular area between the outer wall of the metal casing 1 and a drill hole, and permanently fixing the metal casing 1, the first armored optical cable 4 and the stratum rock together after the cement slurry is solidified;
(4) Synchronously and slowly putting the continuous oil pipe 2 and the second armored optical cable 5 into the well of the metal casing 1 for well cementation and completion;
(5) The second annular metal clips 9 are arranged on the coiled tubing 2 at the wellhead at the same intervals (about 10 meters), so that the second armored optical cable 5 is fixed and protected from being damaged in the installation process of the lower coiled tubing 2, and the second armored optical cable 5 and the coiled tubing 2 have good adherence strain coupling;
(6) Connecting the single-mode optical fiber or the special strain sensitive optical fiber 21 in the first armored optical cable 4 to a DSS signal input end of a DSS/DTS composite modulation and demodulation instrument 3 at a wellhead, and connecting the single multimode optical fiber or the two multimode optical fibers 21 in the first armored optical cable to a DTS signal input end of the DSS/DTS composite modulation and demodulation instrument 3;
(7) Connecting the single-mode optical fiber or the special strain sensitive optical fiber 21 in the second armored optical cable 5 to a DSS signal input end of a DSS/DTS composite modulation and demodulation instrument 3 at a wellhead, and connecting the single multimode optical fiber or the two multimode optical fibers 21 in the second armored optical cable to a DTS signal input end of the DSS/DTS composite modulation and demodulation instrument 3;
(8) During long-term underground strain monitoring and measurement, DSS and DTS signals in a first armored optical cable 4 outside the metal casing 1 and a second armored optical cable 5 outside the coiled tubing 2 are continuously monitored and measured through a DSS/DTS composite modulation and demodulation instrument 3 placed beside a wellhead;
(9) The DSS signal and the DTS signal which are continuously measured by the DSS/DTS composite modulation and demodulation instrument 3 are modulated and demodulated, DSS data are converted into strain which is generated by underground ground stress acting on the metal sleeve 1 and the first armored cable 4 and strain which is generated by underground ground stress acting on the coiled tubing 2 and the second armored cable 5, and DTS data are converted into distribution data of temperature change outside the underground metal sleeve 1 and the coiled tubing 2;
(10) According to the monitored and measured temperature data outside the underground metal casing 1 and the coiled tubing 2, a formula delta lambda/lambda-delta upsilon/upsilon-K is utilized TΔt+KCorrecting DSS measured data by using the temperature value of a specific measurement position to perform scattered light spectrum drift in the optical fiber caused by temperature change, and obtaining a true strain value of the outer wall of the metal sleeve 1 and the outer wall of the continuous oil pipe 2, wherein the temperature influence is eliminated;
(11) Calculating the differential of the strain quantities of the outer wall of the metal casing 1 and the outer wall of the continuous oil pipe 2, which are monitored and measured in real time for a long time, to the time to obtain the change rate of the strain quantities along with the time;
(12) And analyzing the strain and the strain rate (the change rate of the strain along with time) of the outer wall of the metal sleeve 1 and the outer wall of the continuous oil pipe 2 which are monitored and measured in real time for a long time, and timely giving out an early warning or an alarm when finding out that the strain and the strain rate of the metal sleeve 1 and the continuous oil pipe 2 exceed threshold values and possibly cause a well section in which the metal sleeve 1 and the continuous oil pipe 2 are deformed and damaged according to the threshold value standards of the strain and the strain rate of the metal sleeve 1 and the continuous oil pipe 2 set by underground engineering, thereby ensuring the long-term stable, safe and reliable work of an oil-gas production well, a water injection well and a monitoring or.
Claims (9)
1. The underground strain distribution monitoring system based on distributed optical fiber sensing is characterized by comprising a metal sleeve (1), wherein a coiled tubing (2) is arranged in the metal sleeve (1), a first armored optical cable (4) is fixed on the outer side of the metal sleeve (1), and a second armored optical cable (5) is fixed on the outer side of the coiled tubing;
The device also comprises a DSS/DTS composite modulation and demodulation instrument (3) which is arranged near the wellhead; the DSS/DTS composite modulation and demodulation instrument (3) is respectively connected with a first armored optical cable (4) and a second armored optical cable (5).
2. The downhole strain distribution monitoring system based on distributed optical fiber sensing according to claim 1, wherein the DSS/DTS complex modem instrument (3) comprises data acquisition and modem functions of distributed strain sensing and distributed temperature sensing.
3. The downhole strain distribution monitoring system based on distributed optical fiber sensing according to claim 1, wherein the first armored optical cable (4) and the second armored optical cable (5) are both armored optical cables, the armored optical cables comprise optical fibers (21), the optical fibers (21) are single-mode or multi-mode or special strain sensitive optical fibers, and inner continuous metal thin tubes (22) and outer continuous metal thin tubes (23) are sequentially packaged outside the optical fibers (21).
4. A distributed optical fiber sensing based downhole strain distribution monitoring system according to claim 3, wherein the outer continuous metal tubule (23) is further wrapped with one or more layers of armoured steel wire. .
5. The downhole strain distribution monitoring system based on distributed optical fiber sensing of claim 3, wherein the inner continuous metal tubule (22) is further provided with high temperature resistant optical fiber paste; the optical fiber (21) is fixed on the inner wall of the inner continuous metal thin tube (22) by using high temperature resistant epoxy resin (24) at the position with equal distance.
6. The downhole strain distribution monitoring system based on distributed optical fiber sensing according to claim 3, wherein the inner continuous metal thin tube (22) is internally provided with a high-sensitivity strain special optical fiber (21) which is tightly wrapped by a high-temperature-resistant high-strength composite material or is manufactured by wrapping the optical fiber by one-step molding of an injection molding machine, and the high-sensitivity strain special optical fiber is tightly attached to the inner continuous metal thin tube (22) and sealed in the inner continuous metal thin tube.
7. A distributed optical fiber sensing-based downhole strain distribution monitoring system according to claim 1, wherein a plurality of metal sleeves (1) are connected in sequence, and the system further comprises a first annular metal clip (8), wherein the first annular metal clip (8) is fixedly arranged at the boot of the metal sleeves (1).
8. A distributed fibre optic sensing based downhole strain distribution monitoring system according to claim 1, further comprising a second annular metal clip (9), wherein the second annular metal clip (9) is mounted and fixed outside the coiled tubing (2) at equal intervals.
9. The monitoring method of a downhole strain distribution monitoring system based on distributed optical fiber sensing according to any of claims 1 to 8, comprising the steps of:
(a) Synchronously and slowly putting the metal sleeve (1) and the first armored optical cable (4) into a drilled well hole;
(b) The first annular metal clip (8) is arranged at the joint of the two metal sleeves (1) at the wellhead to fix and protect the first armored optical cable (4) from moving and/or being damaged in the casing running process;
(c) After the metal casing (1) is completely put down, pumping cement slurry from the well bottom by using a high-pressure pump truck, returning the cement slurry to the well head from the well bottom along an annular area between the outer wall of the metal casing (1) and a drill hole, and permanently fixing the metal casing (1), the first armored optical cable (4) and stratum rock together after the cement slurry is solidified;
(d) Synchronously and slowly putting the coiled tubing (2) and the second armored optical cable (5) into a metal casing (1) well for well cementation and completion;
(e) The second annular metal clips (9) are arranged on the coiled tubing (2) at a wellhead at the same intervals, and the second armored optical cable (5) is fixed and protected from being damaged in the installation process of the lower coiled tubing (2) and good adherence strain coupling is achieved between the second armored optical cable (5) and the coiled tubing (2);
(f) Connecting optical fibers (21) in the first armored optical cable (4) to a DSS signal input end and a DTS signal input end of a DSS/DTS composite modulation and demodulation instrument (3) at a wellhead respectively;
(g) Connecting optical fibers (21) in the second armored optical cable (5) to a DSS signal input end and a DTS signal input end of the DSS/DTS composite modulation and demodulation instrument (3) at a wellhead respectively;
(h) Continuously monitoring and measuring DSS and DTS signals in a first armored optical cable (4) outside the metal casing (1) and a second armored optical cable (5) outside the coiled tubing (2) by a DSS/DTS composite modulation and demodulation instrument (3) placed beside a wellhead during long-term underground strain monitoring and measurement;
(i) The DSS/DTS composite modulation and demodulation instrument (3) continuously measures DSS signals and DTS signals, converts DSS data into underground ground stress acting on the metal sleeve (1) and the first armored cable (4) and underground ground stress acting on the coiled tubing (2) and the second armored cable (5), and converts DTS data into distribution data of temperature change outside the metal sleeve (1) and the coiled tubing (2);
(j) According to the monitored and measured temperature data outside the underground metal casing (1) and the coiled tubing (2), the formula is utilized:
Δλ/λ＝-Δυ/υ＝KTΔt+K
Wherein λ and υ are average light wavelength and frequency respectively; k TAnd K Temperature and strain standard constants, respectively;
Correcting DSS measured data by using temperature value of a specific measurement position to perform scattered light spectrum drift in the optical fiber caused by temperature change, and obtaining real strain values of the outer wall of the metal sleeve (1) and the outer wall of the continuous oil pipe (2) without temperature influence;
(k) Calculating the differential of the strain quantities of the outer wall of the metal casing (1) and the outer wall of the coiled tubing (2) on time, which are monitored and measured in real time for a long time, so as to obtain the change rate of the strain quantities along with the time;
(l) The strain and the strain rate of the outer wall of the metal casing (1) and the outer wall of the coiled tubing (2) monitored and measured in real time for a long time are analyzed, and when the strain and the strain rate of the metal casing (1) and the coiled tubing (2) exceed threshold values and well sections which are possibly deformed and damaged by the metal casing (1) and the coiled tubing (2) are found out according to strain and strain rate threshold value standards of the metal casing (1) and the coiled tubing (2) set in underground engineering, early warning or alarm is timely provided.
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