GB2479450A

GB2479450A - Measurement of drill fluid particle size distribution

Info

Publication number: GB2479450A
Application number: GB1105826A
Authority: GB
Inventors: David Wood
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-04-07
Filing date: 2011-04-06
Publication date: 2011-10-12
Also published as: GB201105826D0; GB201005757D0

Abstract

Apparatus for measurement of properties of a drilling fluid flowing through a fluid flow circuit of a drilling device has a diverter 102 for diverting a sample of drilling fluid from the drilling fluid flow circuit, a detector device 114 through which the drilling fluid is arranged to flow, so that the detector carries out a measurement of a particle size distribution and solids concentration of the sample. A supply and drainage conduit are connected to the detector, for directing the sample of drilling fluid to and away from said detector device. The diverter typically comprises a manifold 102 with a number of sampling conduits adapted to divert samples from different locations on the drilling fluid circuit into the manifold and to divert said samples from the manifold to the inlet of the detector device. The detector may be an ultrasonic extinction sensor.

Description

APPARATUS AND METHOD

The present invention relates to an apparatus and method for use in a measurement of a physical property of a drilling fluid flowing through a drilling fluid flow circuit. More particularly, the present invention relates to a diverting device for diverting a sample of drilling fluid from the drilling fluid flow circuit for measuring purposes.

To ensure the safe and efficient operation of down-hole drilling in drilling rigs or work-over rigs, a fluid generally referred to as a drilling fluid is circulated into and out of the bore-hole being drilled or a bore-hole which has already been drilled. The drilling fluid is formulated to match the chemical and physical environment of the particular well or type of well being drilled or which has already been drilled. Typically drilling fluids are expensive and are generally recycled as much as possible. Generally, the drilling fluid is pumped into and out of the well by a pump which drives the drilling fluid down through the bore of the drill string and back up out through the annulus which is formed between the drill string and the circumferential wellbore wall. When the drilling fluid is recovered to the surface, it is typically cycled through a system of surface tanks, filters etc, which are used to clean the drilling fluid and to remove debris such as drill cuttings etc, before the drilling fluid is re-circulated down-hole. The density of the drilling fluid is typically controlled so that in use it creates in the well a column of fluid that maintains a positive-hydrostatic pressure within the well bore which allows wells to be drilled and/or repaired safely and efficiently.

As the drilling fluid is circulated within the well bore, materials such as brine, silt and rock are removed from the well bore to the surface by the circulating drilling fluid. The inclusion of such materials can have a detrimental effect on desired properties of the drilling fluid, such as its particle size distribution and solids concentration. To ensure the desired properties of the drilling fluid are maintained within operational parameters, measurements of these properties should be taken at regular intervals.

The particle size distribution of the re-circulated drilling fluid may be determined by various techniques. For particles greater than 45 microns in diameter, wet sieve analysis is a known method, as well as a microscopic image analysis whose size limit at the low end depends on the type of microscope employed. Furthermore, sedimentation can be used for particles from 0.4 micron to 44 micron diameter and a Coulter Counter is available for particles from 0.4 micron to 1200 micron diameter, as well as a laser light scattering diffraction analysis.

The measurement of solids concentrations is typically carried out using a ml, 20 ml or 10 ml retort. The measurement of the solids concentration of a drilling fluid is generally made every six to twelve hours and the results are generally considered to be representative of the whole drilling fluid being circulated within the system at that particular time.

The particle size distribution of drilling fluid for particles smaller than 45 micron is normally not determined while drilling is taking place, although representative samples of field fluid processed by different groups or types of separation equipment can be collected and sent to third party laboratories (e.g. on shore) for processing to allow a more detailed understanding of the efficiency of individual solids separation equipment and whether the equipment is optimally configured for the fluid been processed.

Other more thorough and time consuming tests on the various desired properties of the drilling fluid are generally made every six to twelve hours as required. Such drilling fluid tests require the attention of skilled personnel for relatively long periods of time, and although the results of the drilling fluid tests are of particular importance to the continuing safe and efficient operation of the drilling operation, the results are generally only relevant to the particular batch of drilling mud which has been checked, and cannot be viewed as being representative of the drilling fluid as a whole.

According to an aspect of the invention, there is provided an apparatus for use in measurement of a physical property of a drilling fluid flow circuit of a drilling device, said apparatus comprising:-a diverter configured to divert a sample of drilling fluid from the drilling fluid flow circuit; a detector device having an inlet and an outlet allowing the sample of drilling fluid to flow through said detector device, thereby conducting a measurement of a particle size distribution of the sample of drilling fluid; and a supply and drainage conduit connected to said inlet and outlet respectively, for directing the sample of drilling fluid to and away from said detector device.

Typically, the diverter comprises a pump.

Optionally, the diverter comprises a manifold with a number of sampling conduits adapted to divert samples from spaced apart locations on the drilling fluid circuit into the manifold, and to divert said samples from the manifold to the inlet of the detector device. Thus, a more controlled and representative sample of drilling fluid can be diverted to the measurement apparatus and can be obtained from a number of sample points in the drilling fluid flow circuit and provided to the detector device. Diverting the samples in this manner optionally allows sampling from spaced apart locations of the circuit, to reflect more accurately the characteristics of the drilling fluid from a number of different sample points. Sampling from different spaced apart locations is typically carried out in a short space of time, with the samples being gathered advantageously within one circulation of the fluid in the well bore, or at sequential times that are very close to one another. Optionally, the samples are taken from the annulus bore rather than the production bore, and the diverter is typically adapted to divert samples of drilling fluid from an annulus between a drill string and a bore hole or bore hole casing. In the annulus between the drill string and the bore hole or the bore hole casing, there is typically only a flow of drilling fluid which returns to the surface. The drilling fluid has been pumped downhole within the drill string and is returned to the surface through the annulus between the outside of the drill string and the wall of the hole (which is normally cased or lined). The drilling fluid returning to the surface through the annulus carries large amounts of suspended solids which are produced during drilling and/or washed from the wellbore wall while it flows up through the annulus. Samples taken from the drilling fluid in the annulus can provide useful information on the particle size distribution in the drilling fluid so that the drilling fluid can be suitably prepared for re-circulation down the well to be used for further drilling purposes. The direct measurement from the annulus allows real time determination of the particle size distribution and optionally other physical characteristics of the drilling fluid (e.g. concentration of the sizes of particular particles) while there is still time to condition the drilling fluid (for example to filter it or dilute it, or add more particles of a specific size range) prior to the re-circulation of the fluid back down the hole, so that the fluid being re-circulated back down the hole has a suitable particle size distribution and optionally other physical properties for effective control of the prevailing downhole conditions such as formation pressure etc. Optionally, the apparatus has a sieving device arranged so that samples of drilling fluid pass through the sieving device before passing through the detector device. The sieving device can be arranged to concentrate some particle size ranges and dilute others. The sieving device can for example be a vibrating wet sieving device, and can provide the option of having one, two or three wet sieving decks. The or each wet sieving deck can support and clamp a test sieve and can have a support frame to which a stainless screen mesh with an aperture of between 20 microns and 3000 microns is bonded under tension. The stainless steel wire mesh used to manufacture the test sieves typically complies with ISO 3310-1 and the diameter of the test sieve is typically between 450 mm to 465 mm.

Optionally, the sieving device has a holding tank for collecting a sieved sample of drilling fluid.

Typically, the holding tank has a first outlet for delivering the sieved sample of drilling fluid to a part of the supply conduit. It can optionally have a second outlet operated by a valve to allow a part of the sieved sample of drilling fluid to flow out of the holding tank and to bypass the detector device.

Typically, the apparatus incorporates a mixing chamber having a conduit for a dilution fluid such as base mud or drilling fluid to be added to the mixing chamber, and a conduit for directing the diluted sample of drilling fluid to the detector device.

Optionally, the apparatus incorporates a first sample chamber for sampling a predetermined volume of the sample of drilling fluid, wherein the first sample chamber has a conduit to the mixing chamber for providing the predetermined volume of the sample of drilling fluid to the mixing chamber.

The predetermined volume can be between 50 ml and 1 litre and the first sample chamber can typically be configured to provide repeated suction and discharge of drilling fluid with a solids concentration of more than 50% with a discharge volume of between 50 ml and 1 litre.

Optionally, the apparatus incorporates a second sample chamber for sampling a predetermined volume of the dilution fluid. Typically, the second sample chamber has a conduit to the mixing chamber for providing the predetermined volume of the dilution fluid to the mixing chamber.

Optionally a single sample chamber can suffice.

Typically, the apparatus incorporates a degassing device for removing gas (e.g. gas bubbles) from the sample prior to and/or during circulation of the sample of drilling fluid from the mixing chamber through the supply and return conduit and the detector device. This helps to avoid false detector readings arising from the bubbles being mistaken for solid particles, which may falsify the particle size distribution. It is thus advantageous that the sample analysis takes place in a degassed environment. In particular, it is advantageous to at least reduce the size of the gas bubbles at least to a predetermined extent to minimize their impact on the measurement of the particle size distribution.

Typically, the apparatus incorporates a vacuum generator as degassing device for applying a vacuum to at least one of the mixing chamber and the first sample chamber and, if provided, the second sample chamber prior to and/or during circulation of the sample of drilling fluid from the mixing chamber through the detector device. It is desirable to minimise the presence of entrained gases within the sample of drilling fluid as it passes through the apparatus and more particularly through a measuring zone of the detector, as the presence of bubbles of entrained gas can lead to spurious measurements of the physical properties of the drilling fluid, e.g. as described above. The vacuum generator is connected to the mixing sample chamber to generate and typically maintain a suitable level, for example, 1 in HG to 3Oin HG of vacuum to remove any entrained gases from the sample of drilling fluid that is tested. Typically 1 in HG to 3Oin HG of vacuum is sufficient, but different systems can vary.

The apparatus optionally comprises a drainage device for allowing drainage of the mixing chamber. Then, a further sample from another point in the drilling fluid flow circuit can be directed to and diluted in the drained mixing chamber for being measuring in the detector device. The drainage device can be for example a valve connected to the drainage conduit.

The detector device is typically configured to measure a solids concentration of the sample of drilling fluid.

The detector device is typically an ultrasonic extinction sensor which can optionally comprise an ultrasonic radio frequency generator. In one embodiment, the ultrasonic radio frequency generator forms one side of a measuring zone and an ultrasonic radio frequency detector forms another side of the measuring zone. The detector device can typically measure a solids concentration with particles from 0.01 microns to 3000 microns in suspensions and emulsions of high concentrations.

The sieving device is typically configured to concentrate particles having a particle diameter of between 0.01 pm and 3 mm and to remove or dilute particles outwith this range.

The apparatus is typically formed and arranged in a compact and portable form which can be relatively easily transported to and from a rig site without the need for heavy lifting equipment.

The apparatus typically forms part of an active control system, wherein the apparatus is arranged with a control mechanism which adjusts the composition or other physical property of a drilling fluid when the apparatus detects that a particle size distribution to be measured falls outwith pre-defined operational parameters, so that remedial action can be taken to bring the particle size distribution within said operational parameter.

According to a further aspect of the present invention, there is provided a method for measuring the particle size distribution of a drilling fluid flowing through a drilling fluid flow circuit of a drilling device, said method comprising the steps of diverting a sample of drilling fluid from the drilling fluid flow circuit; directing the sample of drilling fluid through a detector device via a supply and drainage conduit; and measuring a particle size distribution of the sample of drilling fluid using the detector device.

Typically, the sample of drilling fluid is diverted from an annulus between a drill string and a bore hole or bore hole casing.

The method optionally comprises the step of sieving the sample of drilling fluid prior to measuring a particle size distribution of the sample of drilling fluid.

The sample of drilling fluid is typically sieved to concentrate particles having a particle diameter of between 0.01 pm and 3 mm within the sample of drilling fluid.

The method optionally incorporates the step of collecting a sieved sample of drilling fluid in a holding tank.

Typically, the method comprises the step of mixing the sample of drilling fluid in a mixing chamber prior to directing it through the detector device and the step of circulating the sample of drilling fluid through the detector device and the mixing chamber. The sample of drilling fluid is typically re-circulated through the detector device and the mixing chamber for a time period between three and five minutes, for example by using a circulation pump.

Optionally, the method further comprises the step of sampling a predetermined volume of the sample of drilling fluid and providing it to the mixing chamber. Thus, a known volume of the sample of drilling fluid can be directed from the mixing chamber to the detector device, which could facilitate analysis of the sample of drilling fluid.

Further, the method can optionally comprise the step of diluting the sample of drilling fluid by directing a predetermined volume of a dilution fluid into the mixing chamber prior to mixing and circulating the sample of drilling fluid. The sample of drilling fluid can then be mixed with the dilution fluid, and the fluid circulated through the detector device and the mixing chamber will have predetermined properties. The circulated fluid is sometimes also referred to as circulating fluid hereafter.

Typically, the method can incorporate the step of degassing the mixing chamber to remove or at least reduce a size range of gas bubbles which may otherwise be detected as particles and could thus falsify the measured particle size distribution.

Typically, the method further comprises the step of evacuating the mixing chamber from gases entrained with the sample of drilling fluid, for example entrained within the drilling mud.

Typically, the method further comprises the step of cleaning the mixing chamber using dilution fluid after the steps of measuring a particle size distribution. The mixing chamber is typically drained before the cleaning step is executed and/or before a measurement of a next sample of drilling fluid from a point of the drilling fluid flow circuit is executed.

The step of measuring optionally comprises measuring a solids concentration of the drilling fluid.

In certain embodiments of the invention, after the particle size distribution of the sample has been measured the fluid from which the sample was taken is returned to the bore hole. Typically the sample taken can also be returned to the bore hole.

Embodiments of the invention allow a number of physical properties of a drilling fluid to be checked (typically from different parts of the circuit) at different frequencies without delaying the processing of the drilling fluid or the sampling. In many well conditions including during high pressure and high temperature drilling, evaluation and completion works, embodiments allow fluid properties such as the particle size distribution and solids concentration to be optimized in order to ensure the safe and efficient operation of a drilling device using the drilling mud, and even allow continuous monitoring of these and other parameters of the drilling mud as it is being used. Some of these data provide useful indicators about the rheology and equivalent circulating density and assist in maintaining a mud system which yields good well stability, and reduces fluids and fine solids invasion of the formation which can result in a reduction of permeability. Some embodiments allow or facilitate the determination of the average particle size variation and concentration changes over the period of the well and can help to provide a continuous understanding and data collection of the efficiency or inefficacy of each different group or type of separation equipment and/or determine whether the equipment is optimally configured for the fluid been processed. The samples are advantageously taken from drilling fluid for the purpose of analysing the particle size distribution of the drilling fluid in real-time and providing for suitable preparation and filtering of the drilling fluid when it has returned to surface, such that it can be re-circulated into the wellbore for further drilling.

In certain embodiments, the invention allows sampling at the rig site in atmospheric conditions, allowing collection of data on samples at the rig site, which is a significant advantage over laboratory based techniques requiring longer analysis off site. This allows offshore rigs to use embodiments of the invention in "live" drilling fluid cycles, i.e. the sample is typically taken live from a functional circuit of drilling fluid while it is being conditioned at the surface, analysis is performed locally in the offshore environment, and results are typically available locally even before the re-injection of the drilling fluid back into the well. Samples can be taken at multiple different points on the system, either sequentially, or, if more than one sampling device is provided, simultaneously. Samples can be taken at early points in the conditioning cycle before the drilling fluid is conditioned or altered from its in use state as it comes out of the well, and follow up samples can be taken to monitor changes made as a result of the conditioning during the topsides treatment. Particular ranges of particle size distribution can be targeted, for example, fine particles in the 1- 3000um range can be specifically targeted for data returns. Gas content of the sample can be optionally removed from the sample before the sample is taken and discarded.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-Fig. I shows a schematic view of a first apparatus for measuring a physical property of drilling fluid according to an aspect of the present invention; Fig. 2 shows a schematic view of a drilling fluid flow circuit incorporating the apparatus of Fig 1; Fig. 3 is a schematic side view of a part of an alternative embodiment of sampling apparatus similar to the apparatus of Fig 1;Fig. 4 shows a schematic view of an alternative apparatus for measuring a physical property of drilling fluid according to a further embodiment; Fig. 5 shows a schematic view of a drilling fluid flow circuit incorporating the apparatus of Fig 4; Fig. 6 is a side view of a part of an alternative arrangement in the Fig 4 apparatus; and, Fig. 7 shows a graphic presentation of particle size distribution and solids concentration data measured and recorded with the Fig 1 apparatus over a period of 90 hours at 15 minute to 30 minute intervals using samples taken from a drilling fluid circuit in a test well.

In the description which follows, like parts are marked throughout the specification and drawings with the same reference numerals.

Fig. 1 shows an example of an apparatus 100 for use in measurement of the particle size distribution and optionally another physical property of drilling fluid flowing through a drilling fluid flow circuit 200 (Fig. 2) according to an alternative embodiment of the present invention. The entire drilling fluid circuit 200 can be best understood with reference to Fig 2.

Referring to Fig 2, drilling fluid is typically circulated around a flow circuit 200 which typically comprises a down-hole section including bore hole being drilled, and a topsides section of the circuit, which includes various processing apparatus on the rig. The fluid is pumped down through a drill string and emerges from the drill bit at the bottom of the hole. The drilling fluid lubricates the bit as it rotates and washes cuttings drilled from the formation as the drilling fluid is returned topsides to the drilling rig via the annulus between the drill string and the bore hole (typically between the drill string and the bore hole casing). The conduit connecting the annulus to the rig emerges on the deck of the rig and is typically held for processing in at least one holding tank for containing the recovered drilling fluid. When the drilling fluid washes through the annulus, it carries the cuttings and other debris out of the hole. The contaminated drilling fluid emerging from the annulus conduit is then cycled through processing apparatus on the rig to remove cuttings and other debris and to restore the drilling fluid to its original properties before it is re-injected into the well.

The drilling fluid emerging from the annulus is therefore contained in a holding tank before being filtered through a shale shaker 223. The solids are filtered out and the outlet of the shale shaker 223 feeds the filtered drill fluid into a series of tanks such as sand trap 216 to remove sand, a degasser tank 218 to remove bubbles or entrained air, and a second stage desander tank 220 to remove finer sand, followed by a desilter tank 222 to remove fines. Typically the processing step includes one or more stages of centrifugation at 204 and 206, before the processed drilling fluid is passed through a conduit into mud pits 210, 211, 212, and 214, where it is stored and optionally further processed before being pumped back down the well by mud pump 201 via the drill pipe central bore, to emerge once more through the drill bit and to wash more cuttings and other debris up the annulus to the surface in another cycle.

The particle size distribution of the solids in the drilling fluid is subject to many changes during the cycle between the well and the rig. When it emerges from the annulus it is typically heavy with suspended solids.

Typically the topsides processing through the cycle 200 restores the required profile of suspended solids before the drilling fluid is re-injected into the well. The particle size distribution of the drilling fluid is important, because if the fluid is not dense enough because for example, it does not contain sufficient suspended particles, then it loses some capacity to contain blow outs. On the other hand if the drilling fluid becomes too loaded with solids generally, it becomes too difficult to handle, or takes too long to process, and causes excessive wear on the components of the well. Drilling fluid that is injected into the well with the wrong profile of particle size distribution may also damage the formation thereby reducing the amount or value of recoverable production fluids from the well. In most cases, the particulates in the drilling fluid break down as the drilling fluid is re-circulated in the well, and the concentrations of smaller particles increase. If the very fine particles increase beyond a certain threshold then they can plug the formation and reduce the economic value of the well.

The sampling apparatus 100 shown in Fig. 1 is provided at the topsides section of the drilling fluid flow circuit to divert samples of drilling fluid from any predetermined point of the drilling fluid flow circuit 200 for measurements of the particle size distribution (and typically of other physical properties) of the drilling fluid. It can thus provide real time analysis of the drilling fluid and serves to assure a specific quality of the drilling fluid which is circulated through the bore hole, before it is re-injected into the well.

The sampling apparatus 100 comprises a suction manifold 102 with a number, e.g. twelve pneumatically actuated two way ball valves 101. The ball valves 101 have input sampling conduits 202 (Fig. 2) connecting them to different parts of the topsides drilling fluid flow circuit 200 as shown in Fig 2. For example, one valve can control access to the sampling apparatus from the 1st centrifuge tank 204, another from the 2nd centrifuge tank 206, another from the active pit 210, another from the reserve pit 212, and soon. Each separate valve 101 admits fluid sarripled from a discrete point on the drilling fluid circuit 200 and samples are typically reflective of the actual real time conditions in the various centrifuge tanks, pits and filters etc. The valves 101 are normally closed and can be opened by a pneumatic or other signal (e.g. an electric signal) manually or automatically selected in any desired sequence from the pneumatic control cabinet 118 or remotely by a PLC controller (not shown). When a particular valve 101 is selected and opened, a pneumatic signal from the pneumatic control cabinet 118 typically starts a variable speed pump 103.

The pump 103 then draws a sample of drilling fluid from whichever sample point the valve 101 is connected to. The sample typically flows to the valve 101 via a respective conduit 202 dedicated to a particular valve.

The suction manifold 102 and the pump 103, and optionally the particular conduit 202 thus form a diverting device for diverting a sample of drilling fluid from the drilling fluid flow circuit.

Drilling fluids typically contain large amounts of solid and/or semi-solid materials when the drilling fluid returns to, for example, a drilling rig during a drilling operation. While every effort is made to remove the largest of the solids and semi solids materials while they pass through a solids control package such as the screens 223 and tanks 204-218, equipment failures and worn or damaged shale shaker screens can allow larger solids and semi solid particles to remain suspended in the drilling fluid. In order to reduce the possibility of damage to the apparatus 100, the apparatus 100 is typically provided with a self cleaning filter disposed after the pump 103 of the apparatus 100, typically formed and arranged to remove unwanted solid and/or semi-solid materials from the diverted sample of drilling fluid passing through the apparatus 100. The filter is typically a vibrating wet sieving device 104 having the option of being configured with one, two or three wet sieving decks. The uppermost deck could optionally be dressed with a pre-tensioned 500 micron stainless steel wire mesh screen. The middle and lower wet sifting decks may be unmeshed or dressed with suitable screen mesh to allow a visual determination of the upstream shale shaker package actual as against estimated D100 cut point. Alternatively, the meshes can have any aperture in the range from 20 micron to 3000 micron. The vibration of the wet sieving device and passage of a thin layer of the sample of drilling fluid through the wet sieving device can break the liquid film enveloping entrained bubbles allowing release of the entrained gas bubbles to the atmosphere. The possible issue of a transfer of vibrations generated by the wet sieving device to the detector device can optionally be addressed by having them mounted on different modules of the apparatus 100.

The sample of drilling fluid is discharged from the variable speed pump 103 onto the uppermost deck of the three deck vibrating wet sieving device 104. Solids discharged from the wet sieving device 104 can be weighed and visually inspected before they are returned to the drilling fluid flow circuit 200 (Fig. 2).

The sample of drilling fluid without any predetermined sized solid particles which have been removed by the wet sieving device 104 flows into a small holding tank 105. A normally open pneumatically actuated ball valve 1 06A allows the sample of drilling fluid to flow out of the bottom of the small holding tank 105 until a sufficient amount of the sample of drilling fluid has been pumped from the initial sample point to ensure a current and representative sample of drilling fluid has been delivered into the small holding tank 105. Once a current and representative sample of drilling fluid has been discharged into the small holding tank 105, the normally open pneumatic actuated valve 106A is typically closed by a signal (e.g. a pneumatic signal of compressed air) from the pneumatic control cabinet 118. When the valve 1 06A is closed, a variable speed pump 107 is started via a compressed air feed from the pneumatic control cabinet 118.

A normally open pneumatically actuated ball valve 106B allows the sample of drilling fluid and any residual air to flow out of a conduit between a discharge port of the pump 107 and the normally open pneumatically actuated valve 106B.

After a period of time determined by an adjustable pneumatic timer, the normally open pneumatically actuated ball valve 106A receives a pneumatic signal from the pneumatic control cabinet 118 and closes.

Once the valve 106A is closed the variable speed pump 107 dead heads then stops cycling. A vacuum generator 112 receives a controlled compressed air feed from the pneumatic control cabinet 118 and draws a predetermined level of a vacuum on a mixing chamber 111 and on a first and second sample chamber 11OA, hUB.

A pneumatic signal from the pneumatic control cabinet 118 to a pneumatic actuator of a three way L ported ball valve 1 08A cycles the valve 1 08A and the internal (non commutation) L porting of the three way valve I 08A connects the first sample chamber 11 OA, which is under vacuum, to the pressurized representative sample of drilling fluid that is supplied from the variable speed pump 107. A representative sample of drilling fluid with a known volume of between 50m1 and 1 litre flows into the first sample chamber 11 OA and fills under pressure the vacuum void of the first sample chamber 11 OA.

Once the first sample chamber 11 OA is full and pressurized, a pneumatic signal from the pneumatic control cabinet 118 to the pneumatic actuator of three way L ported ball valve 1 08A is cancelled by a logic of the pneumatic control cabinet 118, and a return spring of the pneumatic actuator on ball valve 108A cycles the three way ball valve. This allows the pressurized sample of drilling fluid to flow typically via gravity feed into the mixing chamber 111 which is still retained under vacuum.

If required, a fixed volume of a dilution fluid which is optionally separately held in a tank 116 can be added and mixed to the sample of drilling fluid in the mixing chamber 111 by a variable speed pump 115. The pump 115 is formed and arranged for providing the dilution fluid via a flexible conduit to the second sample chamber 11 OB with a fixed volume of between 50 ml and 1 litre which is connected to the mixing chamber 111 via an air operated, spring return three way L port ball valve 108B. The second sample chamber 11 OB is capable of the repeated suction and discharge of dilution fluid with a discharge volume of between 50m1 and 1 litre formed and arranged to provide a metered volume of dilution fluid into the mixing chamberlil.

The dilution fluid is typically selected to be compatible with the base fluid of the mud system been sampled. In the case of synthetic oil based mud, it could typically comprise the base oil used to build the mud. Typically the dilution fluid limits the ultrasound attenuation spectra and maintains the solids concentration in the samples within suitable ranges.

The pump 115 and a three way L ported ball valve 1 08B can operate in the same way as pump 107 and the corresponding three way L ported ball valve 108A with regard to the first sample chamber 1 1OA for conducting dilution fluid into the second sample chamber 11 OB and from the second sample chamber 11 OB into the mixing chamber 111.

The mixing chamber 111 is typically conical and vertically arranged, and can optionally be manufactured from stainless steel with a lower internal diameter of for example approximately 35 mm and an upper internal diameter of for example approximately 250 mm and an overall height of for example around 275 mm. The mixing chamber 111 typically has four inlets and two outlets with an internal flow dispersion baffle 125 installed in an upper section of the mixing chamber 111. A sight gauge can be positioned between the lower and upper diameters of the mixing chamber 111. The mixing chamber 111 is constructed from a material which is capable of withstanding a vacuum or pressure and which is more or less robust and resistant to corrosion. Typical materials such as steel, particularly stainless steel (especially for use in hostile environment such as those found or sea-based drilling rigs) are suitable for construction of the mixing chamber.

When the required volume and ratio of the sample of drilling fluid and dilution fluid (if required) are held under vacuum in the mixing chamber ill, a controlled compressed air supply from pneumatic control cabinet 118 to a variable speed pump 113 cycles the pump 113 and the content of the mixing chamber 111, also referred to as circulating sample, circulates in a controlled and adjustable manner from a lower outlet 126 of the mixing chamber 111 through to the detector device 114 and through a sensing zone of a detector device, which is for example an ultrasonic extinction sensor 114, and then to an upper inlet 127 (Fig. 3) of the mixing chamber 111. If the sample of drilling fluid is diluted this can be an advantage as this will reduce its viscosity and gel strength and in turn reduce any surface tension of the liquid film that may be enveloping the entertained gas bubbles. Measuring the drilling fluid properties in a vacuum typically reduces the presence of entrained gas bubbles or spurious air bubbles, which can form while mixing and circulating the sample.

An inline stainless steel spiral pipe mixer can be located inside a supply conduit 122 connected to an inlet 120 of the sensor 114 to ensure a turbulent flow and the complete mixing of the circulating sample. The circulating sample flows out through an outlet 121 of the sensor 114 and via a drainage conduit 119 back into the mixing chamber 111. The mixing chamber 111 can circulate one litre to two litres of sample of drilling fluid or the diluted sample when measuring drilling fluid properties.

The sensor 114 can be formed and arranged for continuous measurement of physical properties such the particle size distribution and solids concentration, typically both particle size distribution and solids concentration. The sensor 114 may be any device suitable for direct and/or indirect continuous measurement of particle size distribution of the sample drilling fluid or circulating sample as it passes through the sensor 114. In the present embodiment, the detector typically comprises an ultrasonic extinction sensor. In embodiments of the present invention, the detector device can also be configured to measure a temperature of the drilling fluid or other physical parameters, or more than one physical parameter. The sensor 114 can have a detector or measurement portion in the form of a finger probe with an adjustable measuring zone of between 1 mm and 10mm. The gap of the measuring zone is optionally adjusted and set by a computer (not shown). A split pipe spool 128 (see Fig 3) is typically fixed (e.g. bolted) over the measuring zone of the sensor 114 to allow the recirculation of drilling fluid in the mixing chamber through the measuring zone of the sensor 14 and to return the flow back to the mixing chamber 111.

The cycling time of the variable speed pump 113 is typically determined by an adjustable pneumatic timer in the pneumatic control cabinet 118. The sample of drilling fluid and dilution fluid (if added) will be circulated between three and five minutes. This time is broken down for two minutes circulation to allow the sample of drilling fluid and dilution fluid to fully mix if required and three minutes to allow the sensor 114 to conduct three readings of the particle size and optionally solids concentration of the circulating sample. Particle size distribution and other physical properties of the drilling fluid can be measured by substantially continuous measurement. Individual measurements of said physical property may be made sequentially one after the other with little or no time interval between each said measurement i.e. in near real time. Typically, a time interval between individual measurements can be varied as required from e.g. 30-seconds to several e.g. 1, 2, 3, 4 or more hours between individual measurements.

A computer (not shown), for example a 3.6GHz small frame factor computer with a display monitor (not shown) housed in an ATEX Zone 1 category 2 purged enclosure 117, is typically connected to the sensor 114 via a fibre optical cable 123 and measurements and data collected by the sensor 114 are collected, analyzed by a computer software to present definable properties of particle distribution and solids concentrations or any set of parameters of measurement versus time or any other parameter of measurement. An extension software can optionally be provided to evaluate extinction functions. A data storage device is optionally provided to save the measurements and display them on a computer monitor enclosed in the ATEX Zone 1 category 2 purged enclosure 117. A remote module (not shown) connected to the 3.6GHz small frame factor computer optionally allows the measurements and data collected by the sensor 114 and analyzed by the computer software to be sent via a suitable broadband or satellite link (not shown) to any location or office in the world. Typically an ATEX Zone 1 category 2 keyboard and pointing device 124 is typically used to locally irripute and vary the parameters of the sensor 114.

After the measurements have been conducted, the mixing chamber 111 is drained of the measured circulating sample by the pneumatic logic in the pneumatic control cabinet 118 stopping the supply of compressed air to the vacuum generator 112 and sending a pneumatic signal to two pneumatically actuated ball valves 109. A small representative quantity of the circulating sample that has been analysed can be captured via the lower of the two ball valves 109 which is connected to the supply conduit 122 and sent for comparison analysis by a different sensor or method if required. When the mixing chamber 111 is drained, the ball valves 109A, 109B are closed by cancelation of the pneumatic signal to pneumatic actuators of the ball valves 109. If required, a flushing and cleaning cycle of the mixing chamber 111, the supply and drainage conduit 122, 119 and the measuring zone of the sensor 114 can be carried out by drawing a volume of dilution fluid which is held in the tank 116 using the variable speed pump 115, the second sample chamber 11 OB and the three way L ported ball valve 108B to fill the mixing chamber 111 to a required level and then start the variable speed pump 113 to circulate the dilution fluid through the sensor 114. The flushing cycle can be carried out depending on the type of mud, viscosity and solids content of the drilling fluid being sampled to clean the sensing surfaces in the measuring device. After a flushing cycle of e.g. two minutes, the ball valves 109 can be opened again and the dilution fluid used for flushing is allowed to discharge. The apparatus 100 is then ready to process the next sample of drilling fluid.

The variable displacement pumps 103, 107, 113, 115 provided in the embodiment of the present invention as shown in Fig. 1 can be of any known type suitable for use in pumping drilling fluids. However, it is desirable to provide pumps which are intrinsically "safe" for use in environments such as oil/drilling-rigs, i.e. pumps which have a negligible or reduced possibility of providing an ignition source for combustible materials e.g. hydrocarbon gases and/or liquids which are generally found on oil/drilling-rigs. Particularly suitable pumps are pneumatically driven diaphragm pumps. Such pneumatically driven diaphragm pumps can be driven by compressed air provided from a compressed air source such as for example a cylinder containing compressed air or a compressor unit.

In use the Fig 1 embodiment is installed at a suitable point in the Fig. 2 drilling fluid flow circuit 200.

The drilling fluid flow circuit 200 is typically located on a rig and comprises a conventional solids control and mud process package (e.g. shale shakers, conduits etc) of a drilling rig. It has a pump 201 for circulating drilling fluid through a bore hole, for example an active pit 210, a pill pit 211, a first and/or a second reserve pit 212, 214. The drilling fluid flow circuit 200 has a centrifuge tank 206 tank from which drilling fluid is directed through a conduit 208 into the active pit 210. When the drilling fluid flows out of the wellbore, typically through an annulus which is formed between the drill string and the circumferential wellbore wall, it is directed into a filtering section of the drilling fluid flow circuit which has a sand trap 216, a degasser tank 218, a desander tank 220, a desilter tank 222, a first and a second centrifuge tank 204, 206. In these tanks, the corresponding material, e.g. sand, gas and silt (e.g. fine cuttings) is removed from the drilling fluid. From the active pit 210, the drilling fluid is finally re-circulated into the bore hole with the desired properties.

The sampling apparatus 100 is connected to the drilling fluid flow circuit via the suction manifold 102. Each ball valve 101 of the suction manifold 102 can be connected to a conduit 202 of the drilling fluid flow circuit 200. The conduits 202 are connected to the drilling fluid flow circuit in use at points thereon so as to deliver at least part of the drilling fluid to the apparatus 100 from these points. The drilling fluid passing through the conduits 202 is representative of the drilling fluid at the particular stage of sampling. By connecting the supply conduit to a least one of said points in the drilling fluid flow circuit a more accurate, precise and representative measurement of the physical properties of the drilling fluid being used within the drilling mud flow circuit can be conducted. In this embodiment, typically only one ball valve 101 is not connected to a conduit 202. A sample of drilling fluid is supplied to the apparatus 100 for measurements via the conduits 202 from, inter alia, below the removable stainless steel wire mesh screens 219 located in the shale shakers 223 or the first centrifuge and second tank 204, 206 or from the decanting centrifuges 224, de-weighted mud return conduits 225, 226 or the conduit 208 to active pit 210, of from the active pit 210 itself and from the first and second reserve pits 212, 214.

The conduits 202 may be in the form of flexible or rigid pipes or hoses which can be connected to the drilling fluid flow circuit by suitable connector devices such as screw fittings.

The valves 101 of the suction manifold 102 are operated by signals from the control cabinet 118 (Fig. 1) which allows the selection of a number of representative drilling fluid samples from different storage or circulating tanks or specific solids separation equipment or parts of solids control equipment such as shale shaker screen undertlow in any order or sequence.

Fig. 3 shows a cross section of a part of an alternative embodiment of the apparatus 100' (Fig. 1), with the rrlixing chamber ill' and with the first and second sample chambers 11OA', 11OB' which are different sizes with a fixed volume and connected to the mixing chamber 111 via the three ways L ported pneumatically actuated valves 108A', 108B'. In this example, the first sample chamber 11 OA' has a greater volume than the second sample chamber I lOB'. Fig. 3 also shows the supply and drainage conduits 122', 119' between the mixing chamber 111' and the detector device 114'. The vacuum generator 112', the two ball valves 109' and the variable speed pump 113' are used for cycling the circulating sample through the supply and drainage conduit 119', 122', the detector device 114', and the pipe spool 128'.

Above the lower outlet 126' of the mixing chamber 111', the walls of the conical tank are formed at an angle of around 60 degrees to direct fluid entering the vessel to the bottom of the sample and mixing vessel. The mixing chamber 111' can be drained from the fluid that is held inside via the lower outlet 126' when the lower valve 109' is opened up.

Fig. 4 shows an example of an alternative embodiment of apparatus 300 for use in measurement of the particle size distribution of drilling fluid flowing through a drilling fluid flow circuit 400 (Fig. 5).

The apparatus 300 shown in Fig. 4 is provided at the topsides section of the drilling fluid flow circuit to divert samples of drilling fluid from any predetermined point of the drilling fluid flow circuit 400 for measurements of the particle size distribution (and typically of other physical properties) of the drilling fluid. It can thus provide real time analysis of the drilling fluid and serves to assure a specific quality of the drilling fluid which is circulated through the bore hole, before it is re-injected.

The apparatus 300 comprises a dual suction manifold 302 with multiple two way ball valves 301. The ball valves 301 have input sampling conduits 402 (Fig. 5) connecting them to different parts of the topsides drilling fluid flow circuit 400 as shown in Fig. 5. Referring to Fig. 5, the drilling fluid flow circuit 400 is similar to the drilling fluid flow circuit 200 shown in Fig. 2, but includes two variable speed pumps 303A and 303B which pump the sample of drilling fluid from the respective sample points to the apparatus 300.

The ball valves 301 operate as described in relation to ball valves 101 shown in Fig. 1, e.g. one valve can control access to the sampling apparatus 300 from the 1st centrifuge tank 404, another from the 2nd centrifuge tank 406, another from the active pit 410, another from the reserve pit 412, and so on. Each separate valve 301 admits fluid sampled from a discrete point on the drilling fluid circuit 400 and samples are typically reflective of the actual real time conditions in the various centrifuge tanks, pits and filters etc. The valves 301 are normally closed and can be opened by a signal (e.g. a pneumatic signal) which can optionally be automatically selected in any desired sequence from respective pneumatic control cabinets 318 B or 31 8C which are remotely controlled by a PLC controller (not shown). When a valve 301 is selected and opened, a pneumatic signal from a pneumatic control cabinet 318 B or 3180 typically starts a variable speed pump 303A or 303B (depending on the valve 301 and sampling location selected). The pump 303 A or B then draws a sample of drilling fluid from whichever sample point the valve 301 is connected to. The sample typically flows to the valve 301 via a respective conduit 402. The suction manifold 302 and the pump 303 A or B, and optionally the conduit 402 thus form a diverting device for diverting a sample of drilling fluid from the drilling fluid flow circuit 400. Optionally variable speed pump 307 can also draw a sample of drilling fluid from a separate sample point anywhere within the drilling circuit 400.

The sample of drilling fluid is pumped from the initial sample point to ensure a current and representative sample of drilling fluid has been sampled in real time and delivered past a flow restrictor 305 and past non-return valves 306 a, b,c. The function of the flow restrictor 305 is to maintain a positive pressure of between 10 psi and 50 psi within the representative sample flow of drilling fluid. Non return valves 306 a, b, c ensure this pressure is not depleted by passing into other sample conduits.

After a period of time which can optionally be determined by a process logic controller (not shown), a vacuum generator 312 receives a signal typically in the form of a controlled compressed air feed from the pneumatic control cabinet 318 A and draws a predetermined level of a vacuum on a mixing chamber 311 and sample chamber 310.

A pneumatic signal from the pneumatic control cabinet 318 A to a pneumatic actuator of a normally open 2 I 2 way piston operated diaphragm valve 308A cycles and the valve 308A closes, thereby sealing the conduit between sample chamber 31 0A,, and mixing chamber 311 which are both under vacuum.

A pneumatic signal from the pneumatic control cabinet 318 A to a pneumatic actuator of a normally closed 2 I 2 way piston operated diaphragm valve 308 B cycles and the valve 308B opens. Thereby, an open conduit is established between sample chamber 310, which is under vacuum, and the pressurized representative sample of drilling fluid that is supplied from the variable speed pumps 303A, 303B or 307. A representative sample of drilling fluid with a known volume of between 5Orril and 1 litre flows into the sample chamber 310 and fills under pressure the vacuum void of the sample chamber 310.

Once the sample chamber 310 is full and pressurized, a pneumatic signal from the pneumatic control cabinet 318 A to the pneumatic actuator of normally closed 2 / 2 way piston operated diaphragm valve 308 B is cancelled, and a return spring of the pneumatic actuator normally closed 2 I 2 way piston operated diaphragm valve 308 B cycles and the conduit between the pressurized representative sample of drilling fluid being supplied from the variable speed pumps 303A, 303 B or 307 and sample chamber 310 is closed. The pneumatic signal from the pneumatic control cabinet 318 A to the pneumatic actuator of normally open 2 I 2 way piston operated diaphragm valve 308 A is cancelled by a logic of the pneumatic control cabinet 31 8A, and a return spring of the pneumatic actuator normally open 2 I 2 way piston operated diaphragm valve 308 A cycles This allows the pressurized sample of drilling fluid to flow via gravity feed from the sample chamber 310 into the mixing chamber 311 which is still retained under vacuum.

If required, a fixed volume of a dilution fluid which is held in a tank 316 can be added and mixed to the sample of drilling fluid in the mixing chamber 311 by a variable speed pump 315. The pump 315 is formed and arranged for providing the dilution fluid via a flexible conduit and the normally closed 2 / 2 way piston operated diaphragm valve 308 C to the sample chamber 310 with a fixed volume of between 50 ml and 1 litre which is connected to the mixing chamber 311 via an normally open 2 /2 way piston operated diaphragm valve 308 A. The sample chamber 310 is capable of the repeated suction and discharge of dilution fluid with a discharge volume of between 5Oml and 1 litre formed and arranged to provide a metered volume of dilution fluid into the mixing chamber 311.

The pump 315 and 2/2 way piston operated diaphragm valves 308 C and 308A can operate in the same way as pumps 303A, 303B, 307 and the corresponding 2 / 2 way piston operated diaphragm valves 308B and 308A with regard to the sample chamber 310 for conducting dilution fluid into the sample chamber 310 and into the mixing chamber 311.

The mixing chamber 311 is typically conical and vertically arranged, and can optionally be manufactured from stainless steel with a lower internal diameter of for example approximately 35 mm and an upper internal diameter of for example approximately 250 mm and an overall height of for example around 275 mm. The mixing chamber 311 typically has two inlets and two outlets with an internal flow dispersion baffle 325 installed in an upper section of the mixing chamber 311. A sight gauge can be positioned between the lower and upper diameters of the mixing chamber 311. The mixing chamber 311 is constructed from a material which is capable of withstanding a vacuum or pressure and which is more or less robust and resistant to corrosion. Typical materials such as steel, particularly stainless steel (especially for use in hostile environment such as those found or sea-based drilling rigs) are suitable for construction of the mixing chamber.

When the required volume and ratio of the sample of drilling fluid and dilution fluid (if required) are held under vacuum in the mixing chamber 111, a controlled compressed air supply from pneumatic control cabinet 318A to a variable speed pump 313 cycles the pump 313 and the content of the mixing chamber 311, also referred to as circulating sample, circulates in a controlled and adjustable manner from a lower outlet 321 of the mixing chamber 311 through the detector device 314 and through a sensing zone of a detector device 314, which is for example an ultrasonic extinction sensor, and then to an upper inlet 327 (Fig. 6) of the mixing chamber 311. If the sample of drilling fluid is diluted this can be an advantage as this will reduce its viscosity and gel strength and in turn reduce any surface tension of the liquid film that may be enveloping the entertained gas bubbles. As also described above, measuring the drilling fluid properties in a vacuum typically reduces the presence of entrained gas bubbles or spurious air bubbles, which can form while mixing and circulating the sample.

An inline stainless steel spiral pipe mixer can be located inside a supply conduit 319 connected to an inlet 327 of the mixing chamber 311 to ensure a turbulent flow and the complete mixing of the circulating sample arriving into the mixing chamber 311 and subsequently drawn through the sensor 314. The circulating sample flows out through an outlet 322 of the sensor 314 and via a conduit 319 back into the mixing chamber 311. The mixing chamber 311 can circulate one litre to two litres of sample of drilling fluid or the diluted sample when measuring drilling fluid properties.

The sensor 314 can be formed and arranged for continuous measurement of physical properties such the particle size distribution and solids concentration, typically both particle size distribution and solids concentration. The sensor 314 is typically designed similar to the sensor 114 as described with regard to Fig. 1,2 and 3. A split pipe spool 328 (see Fig. 6)is fixed (e.g. bolted) over the measuring zone of the sensor 314 to allow the recirculation of drilling fluid in the mixing chamber through the measuring zone of the sensor 314 and to return the flow back to the mixing chamber 311.

A cycling time of the variable speed pump 313 is determined by the Process Logic Controller (not shown) located in purged enclosure 317.

The sample of drilling fluid and dilution fluid (if added) will be circulated between three and five minutes. This time is broken down for two minutes circulation to allow the sample of drilling fluid and dilution fluid to fully mix if required and three minutes to allow the sensor 314 to conduct three readings of the particle size and solids concentration of the circulating sample. Particle size distribution and other physical properties of the drilling fluid can be measured by substantially continuous measurement.

Individual measurements of said physical property may be made sequentially one after the other with little or no time interval between each said measurement i.e. in near real time. Typically, a time interval between individual measurements can be varied as required from e.g. 30-60 seconds to several e.g. 1, 2, 3, 4 or more hours between individual measurements.

A computer (not shown), for example a 3.6GHz small frame factor computer with a display monitor (not shown) housed in an ATEX Zone 1 category 2 purged enclosure 317, is connected to the sensor 314 via a fibre optical cable 323 and measurements and data collected by the ultrasonic extinction sensor 314 are collected, analyzed by a computer software to present definable properties of particle distribution and solids concentrations or any set of parameters of measurement versus time or any other parameter of measurement. An extension software can be provided to evaluate extinction functions. A data storage device is provided to save the measurements and display them on a computer monitor enclosed in the ATEX Zone 1 category 2 purged enclosure 317. A remote module ( not shown) connected to the 3.6GHz small frame factor computer allows the measurements and data collected by the sensor 314 and analyzed by the computer software to be sent via a suitable broadband or satellite link (not shown) to any location or office in the world. An ATEX Zone 1 category 2 keyboard and pointing device 324 is used to locally impute and vary the parameters of the ultrasonic extinction sensor 314.

After the measurements have been conducted, the mixing chamber 311 is drained of the measured circulating sample by the process logic controller (not shown) managing pneumatic valves located in the pneumatic control cabinet 318A and stopping the supply compressed air to the vacuum generator 312 and sending a pneumatic signal to pneumatically actuated ball valves 309. A small representative quantity of the circulating sample that has been analysed can be captured via the ball valve 309 which is connected to the draining conduit 326 and sent for comparison analysis by a different sensor or method if required. When the mixing chamber 311 is drained, the ball valve 309 is closed by cancelation of the pneumatic signal to pneumatic actuator of the ball valve 309. If required, a flushing and cleaning cycle of the mixing chamber 311, the supply and drainage conduit 319, 326, 327 and the measuring zone of the sensor 314 can be carried out by drawing a volume of dilution fluid which is held in the tank 316 using the variable speed pump 315, the sample chamber 310 and the and 2 / 2 way piston operated diaphragm valves 308 C and 308A to fill the mixing chamber 311 to a required level and then start the variable speed pump 313 to circulate the dilution fluid through the sensor 314. The flushing cycle can be carried out depending on the type of mud, viscosity and solids content of the drilling fluid being sampled to clean the sensing surfaces in the measuring device. After a for example two minutes flushing cycle, the ball valve 309 can be opened again and the dilution fluid used for flushing is allowed to discharge. The apparatus 300 (Fig. 4) is then ready to process the next sample of drilling fluid.

The variable displacement pumps 303A, 303B, 307, 313, 315 provided in the embodiment of the present invention as shown in Fig. 4 can be of any known type suitable for use in pumping drilling fluids. However, it is desirable to provide pumps which are intrinsically "safe" for use in environments such as oil/drilling-rigs, i.e. pumps which have a negligible or reduced possibility of providing an ignition source for combustible materials e.g. hydrocarbon gases and/or liquids which are generally found on oil/drilling-rigs. Particularly, suitable pumps are pneumatically driven diaphragm pumps. Such pneumatically driven diaphragm pumps can be driven by compressed air provided from a compressed air source such as for example a cylinder containing compressed air or a compressor unit.

Fig. 6 shows a cross section of a part of an alternative embodiment of the apparatus 300' (Fig. 4), with a mixing chamber 311' and a sample chamber 310' with a fixed volume and connected to the mixing chamber 311' via a 2/2 way piston operated diaphragm valve 308A'. Fig. 6 also shows the supply and drainage conduits 319', 327', 326' connecting to the mixing chamber 311' and the sensor 314'. This embodiment has a vacuum generator 312', a ball valve 309' and a variable speed pump 313' used for cycling the circulating sample through the supply and drainage conduit 319', 327', 326', and the sensor 314, and pipe spool 328.

Above the lower outlet 321' of the mixing chamber 311', the walls of the conical tank are typically formed at an angle of around 60 degrees to direct fluid entering the vessel to the bottom of the sample and mixing vessel. The mixing chamber 311' can be drained from the fluid that is held inside via the lower outlet 326' when the lower valve 309' is opened up.

Table 1 below shows particle size distribution and solids concentration data measured and recorded with the Fig 1 apparatus using samples taken from a drilling fluid circuit in a test well. The data presented in table 1 were measured and recorded automatically using the method as described above. The sampling was conducted in a test well over a period of 3 hours and 20 minutes at 15 minute intervals. Table 1 shows the variation in the physical parameters, notably the size distribution of the particles during the course of the test. In table 1, the xl 0, x50 and x90 values show the thresholds of particle sizes for the corresponding percentages of the particles. The actual particle size (in microns) is given for the measurements at different points of time for the xl 0, x50, and x90.

For example, the xl 0 value shows the particle size threshold for the bottom 10% of the particles. Therefore in the sample taken at 04.5909, 10% of particles in the sample were below a particle size of 2.llum. The x50 value shows the particle size threshold for the bottom 50% of the particles, so at the same sampling time, the results show that 50% of the particles were below 1 2.77um. The x90 values show the threshold for the bottom 90% of the particles, and so at the same sampling time, 90 % of particles were below a particle size of 55.46urn.

The DQ3 data in table 1 is the % concentration of particles in the fluid in a particular range. In the examples shown the range of the DQ3 data was set to sample all particles having a size range between 35 and 45 urn but this can be set to measure any range of sizes. The 35-45 um range was selected in this particular example as most mud re-conditioning programs add particulates into the drilling fluid in this size range so monitoring the particular size range to determine the concentration of the range is important to decide how much and what size distribution of fresh particulates in the range are to be added to the drilling fluid.

The CV0I data expressed in Table 1 is the total % concentration of particles in the whole sample.

Fig. 7 shows a graphic presentation of particle size distribution and solids concentration data measured and recorded automatically with apparatus and method as described above in a separate test over a period of 90 hours at 15 minute to 30 minute intervals.

The results in Fig 7 and table I show that the distribution of particle sizes remains relatively constant throughout the test. Generally as the cycling drilling fluid breaks down in a system, the concentration of very small particles (the lowest 10%) increases and the x90 decreases. The spikes in the percentage of complete particles (CV0I) showing in the test results arose from mechanical failures of valves during the test, rather than being attributable to deliberate changes introduced to condition the drilling fluid or normal comminution of the particles as the drilling fluid breaks down.

Both the particle size distribution and the different concentration of particles and total concentration of particle in a drilling fluid are important and are both used to understand the changing properties of the circulating fluid system.

Modifications and improvements can be incorporated without departing from the scope of the invention. In particular, valves can be changed without departing from the scope of the invention. The method of controlling the valves in the embodiments presented is typically pneumatic, but could be electronic or some other method.

Table 1

Time xlO(um) x50(um) x90(um) DQ3(45-35):% CVoI:% 04:59:09 2.11 12.77 55.46 4.97 57.56 05:14:42 2.00 11.80 57.86 4.10 41.2 05:30:14 1.90 10.80 52.09 2.63 43.81 05:45:48 1.94 11.20 56.24 3.25 41.33 06:01:20 1.91 10.95 55.62 2.80 42.44 06:16:53 1.96 11.41 52.64 3.57 44.93 06:32:25 1.92 11.00 52.71 3.00 41.04 06:48:00 1.96 11.43 59.49 3.29 39.72 07:03:33 2.04 12.08 61.79 3.90 40.89 07:19:06 1.99 11.68 56.44 3.71 43.04 07:34:27 2.06 12.36 55.06 4.44 58.26 07:50:14 2.09 12.62 57.48 4.67 55.29 08:05:44 2.00 11.79 61.09 3.58 41.86 08:21:19 2.05 12.16 65.81 3.59 40.76

Claims

CLAIMS1. Apparatus suitable for use in measurement of a physical property of a drilling fluid flowing through a drilling fluid flow circuit of a drilling device, said apparatus comprising a diverter for diverting a sample of drilling fluid from the drilling fluid flow circuit; a detector device having an inlet and an outlet allowing the sample of drilling fluid to flow through said detector device, thereby conducting a measurement of a particle size distribution of the sample of drilling fluid; and a supply and drainage conduit connected to said inlet and outlet respectively, for directing the sample of drilling fluid to and away from said detector device.
2. Apparatus as claimed in claim 1, wherein the diverter comprises a pump.
3. Apparatus as claimed in claim 2, wherein the diverter comprises a manifold with a number of sampling conduits adapted to divert samples from spaced apart locations on the drilling fluid circuit into the manifold, and to divert said samples from the manifold to the inlet of the detector device.
4. Apparatus as claimed in claim 2 or 3, wherein the diverter is adapted to divert samples of drilling fluid from an annulus between a drill string and a bore hole or bore hole casing.
5. Apparatus as claimed in any of claims I to 4, having a sieving device arranged so that samples of drilling fluid pass through the sieving device before passing through the detector device.
6. Apparatus as claimed in claim 5, wherein the sieving device has a holding tank for collecting a sieved sample of drilling fluid.
7. Apparatus as claimed in claim 6, wherein the holding tank has a first outlet for delivering the sieved sample of drilling fluid to a part of the supply conduit, and a second outlet operated by a valve to allow a part of the sieved sample of drilling fluid to flow out of the holding tank and to bypass the detector device.
8. Apparatus as claimed in any preceding claim, incorporating a mixing chamber having a conduit for a dilution fluid to be added to the mixing chamber, and a conduit for directing the diluted sample of drilling fluid to the detector device.
9. Apparatus as claimed in claim 8, incorporating a first sample chamber for sampling a predetermined volume of the sample of drilling fluid, wherein the first sample chamber has a conduit to the mixing chamber for providing the predetermined volume of the sample of drilling fluid to the mixing chamber.
10. Apparatus as claimed in claim 8 and 9, incorporating a second sample chamber for sampling a predetermined volume of the dilution fluid, wherein the second sample chamber has a conduit to the mixing chamber for providing the predetermined volume of the dilution fluid to the mixing chamber.
11. Apparatus as claimed in claim 9 or 10, incorporating a degassing device for removing gas from the sample prior to and/or during circulation of the sample of drilling fluid from the mixing chamber through the supply and return conduit and the detector device.
12. Apparatus as claimed in claim 11, wherein the degassing device is adapted to remove gas bubbles from the sample.
13. Apparatus as claimed in claim 9 and 11 or 12, wherein the degassing device is a vacuum generator for applying a vacuum to at least one of the mixing chamber and the first sample chamber prior to and/or during circulation of the sample of drilling fluid from the mixing chamber through the supply and return conduit and the detector device.
14. Apparatus as claimed in claim 10 and 11 or 12, wherein the degassing device is a vacuum generator for applying a vacuum to at least one of the mixing chamber and the first and second sample chambers prior to and/or during circulation of the sample of drilling fluid from the mixing chamber through the supply and return conduit and the detector device.
15. Apparatus as claimed in any of claims 8 to 14, comprising a drainage device for allowing a drainage of the mixing chamber.
16. Apparatus as claimed in any preceding claim, wherein the detector device is capable of measuring a solids concentration of the sample of drilling fluid.
17. An apparatus as claimed in any preceding claim, wherein the detector device comprises an ultrasonic extinction sensor.
18. Apparatus as claimed in claim 17, wherein the ultrasonic extinction sensor comprises an ultrasonic radio frequency generator forming one side of a measuring zone and an ultrasonic radio frequency detector forming another side of the measuring zone.
19. Apparatus as claimed in any of claims 5 to 18, wherein the sieving device is configured to concentrate particles having a particle diameter of between 0.01 pm and 3 mm and to remove or dilute particles outwith this range.
20. A method for measuring a physical property of a drilling fluid flowing through a drilling fluid flow circuit of a drilling device, said method comprising the steps of diverting a sample of drilling fluid from the drilling fluid flow circuit; directing the sample of drilling fluid through a detector device via a supply and drainage conduit; and measuring a particle size distribution of the sample of drilling fluid using the detector device.
21. A method as claimed in claim 20, wherein the sample of drilling fluid is diverted from an annulus between a drill string and a bore hole or bore hole casing.
22. A method as claimed in claim 16 or 17, incorporating the step of sieving the sample of drilling fluid prior to measuring the particle size distribution of the sample of drilling fluid.
23. A method as claimed in claim 22, wherein the sample of drilling fluid is sieved to concentrate particles having a particle diameter of between 0.01 pm and 3mm within the sample of drilling fluid.
24. A method as claimed in claim 22 or 23, incorporating the step of collecting a sieved sample of drilling fluid in a holding tank.
25. A method as claimed in any of claims 20 to 24, incorporating the step of mixing the sample of drilling fluid in a mixing chamber prior to directing it through the detector device and the step of circulating the sample of drilling fluid through the detector device and the mixing chamber.
26. A method as claimed in claim 25, wherein the sample of drilling fluid is re-circulated through the detector device and the mixing chamber for a time period between three and five minutes.
27. A method as claimed in claim 25 or 26, incorporating the step of sampling a predetermined volume of the sample of drilling fluid and providing it to the mixing chamber.
28. A method as claimed in claim 25, 26 or 27, incorporating the step of diluting the sample of drilling fluid by directing a predetermined volume of a dilution fluid into the mixing chamber prior to mixing and circulating the sample of drilling fluid.
29. A method as claimed in any of claims 20 to 28, incorporating the step of degassing the sample before measuring the particle size distribution.
30. A method as claimed in any of claims 25 to 29, incorporating the step of evacuating gasses from the mixing chamber.
31. A method as claimed in any of claims 25 to 30, incorporating the step of draining the mixing chamber from the sample of drilling fluid after measuring a particle size distribution of the sample of drilling fluid.
32. A method as claimed in claim 25 to 31, incorporating the step of cleaning the mixing chamber using dilution fluid after the step of measuring.
33. A method as claimed in any one of claims 20 to 32, wherein the step of measuring comprises measuring a solids concentration.
34. A method as claimed in any one of claims 20 to 33, wherein sequential drilling fluid samples are taken from different parts of a drilling fluid flow circuit and are diverted through sampling conduits to the detector device via the supply and drainage conduit; and wherein the particle size distribution of the samples of drilling fluid are measured sequentially in the detector device.
35. A method as claimed in claim 34, wherein the time interval between each sequential sample of drilling fluid being delivered to the detector device is controlled by a processing device.
36. A method as claimed in claim 34 or 35, wherein the time interval between each sequential sample being delivered to the detector device is less than 1 minute.