FIELD

The present disclosure relates to an injection apparatus and method, for example for use in injecting a fluid or other material into a flowline, such as a flowline associated with wellbore operations.

BACKGROUND

Many industries, such as the oil and gas industry, manage the flow of fluids through flowlines, such as is the case of flowing produced hydrocarbons from subterranean reservoirs. Many processes might require the injection of a desired medium into such flowlines, for example to facilitate treatment of the flowlines, treatment of the fluid under transport, and/or for use in performing testing of associated equipment such as sensors, detectors, meters and the like. As will be discussed in more detail below, it is known in the art to inject a known quantity of sand into a hydrocarbon flowline for the purpose of field testing sand detectors which are operatively associated with the flowline to detect any sand which might also be produced with the hydrocarbons.

In this respect sand production from unconsolidated formations in oil and gas wells has been a worldwide challenge for the petroleum industry for many decades. The challenge is not merely to avoid or stop sand production, but to be able to maintain commercial well productivity after efforts to control sand are implemented. At the same time, the control method selected must be justified by a reasonable payback time of the investment cost.

Produced sand is a major problem in many production situations since small amounts of sand entrained in the produced fluid can result in significant erosion and erosioncorrosion problems. Even in "sand free" or clean service situations where the sand production rate is minimal, erosion damage could be very severe at high production velocities. Sand erosion can also cause localized erosion damage to protective films on pipe walls and result in accelerated erosion-corrosion damage. In a high velocity gas well, sand erosion is a serious problem since it can erode holes in the pipework in a very short time period. When sand is produced, it usually does so in batches or slugs. However, the time period for the batches can vary both for the individual well itself as from well to well. When sand has been produced constantly over a period of time, one should be aware of the conditions within the reservoir itself.

Erosion, corrosion and erosion-corrosion problems provide significant safety and environmental risks to the oil and gas industry due to unexpected material failure. In addition the cost associated with such failures is estimated to be many millions of dollars each year due to deferred or lost production and repair costs.

It is therefore desirable in many cases to monitor produced sand, and by using a monitoring device with a high degree of repeatability and sensitivity, producers are able to avoid or properly manage erosion, corrosion, and reservoir damage, but can also increase the oil and gas production rate.

Various types of sand detector exist, including an acoustic sand detector which is a nonintrusive sand monitoring system that identifies in real-time sand production in any water, oil, gas or multiphase flow lines for onshore and offshore locations. Such detectors offer a cost effective means for operators to optimise production by enabling the determination of maximum sand free rates or maximum acceptable sand production rates.

Sand-monitoring terminology such as calibration, accuracy, and repeatability can sometimes be confusing. For some oil producers, accuracy is not of great importance as their main concern is repeatability. Other oil production systems may instead prefer a high degree of accuracy, for example because the volume of sand produced is a concern. In such cases, producers are concerned about how the sand affects the piping (e.g., erosion), how the sand affects the reservoir itself, when do they have to clean out a sand separator, etc.

As noted above, it is known in the art to field test sand detector systems by injecting a known quantity of sand into the flowline upstream of the detector, to ensure accuracy and/or repeatability is present, and perhaps assist with a calibration process to ensure any detector adjustment might be required. Known sand injector systems include a sand injection pump system which typically includes a tank filled with a suspension of sand, a high-pressure hose with a series of ball valves and a check valve, wherein one end of the hose is connected to the tank and the other end to an injection point on the flowline upstream of the sand detector instruments. The injector system will typically also include a pneumatic panel, which houses the controls, gauges and a pump, which thus brings a degree of cost and complexity.

SUMMARY

An aspect of the present disclosure relates to an injection apparatus for injecting an injection medium into a flowline from a location externally of the flowline, the apparatus comprising: a housing; a piston mounted in the housing and defining a moving barrier between first and second chambers within the housing, wherein the first chamber is for containing an injection medium and the second chamber is for containing a pressurised driving gas; and a selectively openable injection outlet in communication with the first chamber, wherein the injection outlet is connectable to the flowline, wherein, in use, the injection apparatus is external to the flowline, and when the injection outlet is opened pressurised driving gas in the second chamber is permitted to expand and drive the piston member in a direction to reduce the volume of the first chamber and eject injection medium therefrom via the injection outlet and into a connected flowline.

Thus, energy required to eject the injection medium from the first chamber is derived from the internal gas pressure of the driving gas, which may provide significant advantages. For example, the injection apparatus, when charged with injection medium and pressurised driving gas, may be considered to be a self-contained system, minimising complexities of multiple interconnected systems and apparatus. In some examples this may eliminate any requirement to use pump systems at the time of injection, which is typically the case in the prior art. This may, for example, reduce capital and operational costs, may minimise failure modes, may minimise operator complexities and thus require less operating personnel, and may accommodate a more compact system which may be of benefit in deployments where space is at a premium. Electrical supply requirements may also be eliminated at the time of injection, for example as there may be no requirement to drive a pump and associated control equipment. This may benefit any application, especially where electrical supply is difficult to provide, as might be the case in remote locations, offshore, subsea environments, subterranean locations and the like. Further, the lack of any required electrical supply at the time of injection may facilitate more ready adherence to certain regulatory requirements such as the ATEX directive relating to equipment used in an explosive atmosphere.

Also, the requirement for any external pressure supply may be minimised, or any source of water supply or other fluid which might otherwise be required to flush, displace or inject medium into a flowline.

Furthermore, by virtue of being a self-contained system the apparatus may be more mobile and more readily deployable and handled. Further, the apparatus may be readily scalable, for example by suitable selection of the size of the housing and thus achievable volume of the first and second chambers, by interconnection of multiple injection apparatus, for example via a manifold, and/or the like.

Also, by virtue of being a self-contained system safety benefits may be derived. For example, with the gas pressure pre-set, an operator may not be capable of causing the device to be over-pressurised when in use.

Moreover, injection apparatuses in accordance with the present disclosure may be capable of obtaining accreditation, such as for transportation in a pre-charged state, e.g. with pressurised driving gas. Such accreditations may be obtained under the United States Department of Transport (Special Permit), the Pressure Equipment Directive under EU regulations (TPED I PED) and Transport Canada, as well as under Australian standards, for example.

Further, as the injection medium is effectively pre-charged or loaded in the injection apparatus, the actual volume of injection medium injected may be more precisely controlled. This contrasts with prior art systems in which medium is pumped from a storage tank with the injected volume being indirectly controlled in accordance with the control of injection flow rate.

The first chamber by virtue of holding the injection medium may be defined as an injection chamber. The second chamber by virtue of holding the pressurised drive gas may be defined as a drive chamber.

The injection apparatus may be used in any number of applications for injecting an injection medium into any flowline. In some examples the flowline may be associated with wellbore operations, such as the production of hydrocarbons and associated components (such as water, solids etc.) from a wellbore, the production of water from a wellbore, the injection of fluids (e.g., water, gas etc.) into a wellbore, and the like. In this respect the injection apparatus may be for injecting an injection medium into a well flowline. In some examples a well flowline may be considered to be any flowline which handles fluids, with or without any solids content, which are produced from or being injected into a wellbore. As such, an aspect of the present disclosure relates to an injection apparatus for use in injecting an injectable medium into a well flowline. The well flowline may be located at an onshore location, offshore location, topside location, subsea location and/or the like.

In some examples the flowline may be associated with the flow of hydrocarbons, such as hydrocarbon production flowlines. In some examples a hydrocarbon flowline may be considered to be any flowline which handles hydrocarbons at any stage following their flow from a subterranean hydrocarbon bearing formation. As such, an aspect of the present disclosure relates to an injection apparatus for use in injecting an injectable medium into a hydrocarbon flowline. The hydrocarbon flowline may be located at an onshore location, offshore location, topside location, subsea location and/or the like.

The flowline may comprise, for example, a pipe or pipe system, a manifold, a tool string or any other apparatus which accommodates flow, a wellhead, production tree, injection tree, Blow Out Preventer (BOP), landing string, lubricator stack and/or the like.

The injection device may be for use in injecting any desired injection medium into a flowline, such as into a well flowline. The injection medium may comprise a fluid (including liquids, gases and mixtures thereof), a gel, a mixture, a solution, particulate material, a suspension, a solvent, and/or the like.

In one example the injection medium may comprise a treatment for use in performing a treatment function in the flowline, for example to the flowline itself (e.g., pipework) and/or to fluid flowing within the flowline. The injection medium may, for example, be configured to remove material (e.g., wax, paraffin, asphaltenes etc.) deposited within the flowline. In such examples the treatment medium may comprise a solvent, surfactant, dispersant, foaming agent and/or the like. The injection medium may be configured to perform a treatment within the flowline by altering a property of fluid flowing therein. For example, the injection medium may function to modify fluid density, viscosity and/or the like. Such treatment of fluid flowing within the flowline may perform one or more functions, such as to assist with recovery rates, as a precursor to subsequent treatment, to protect associated flow equipment such as pumps, and/or the like.

The injection medium may comprise a tracer which may be configured for detection at a location within the flowline, for example downstream of the point of injection into the flowline. The tracer may comprise a chemical tracer, radioactive tracer, EM tracer (e.g., RFID tag), acoustic tracer and/or the like.

The injection medium may comprise a particulate material (e.g., a solid particulate material). Thus, an aspect of the present disclosure relates to a particulate injection apparatus for injecting a particulate material into a flowline. The particulate material may comprise sand particles. Alternatively, or additionally, the particulate material may comprise a proppant material, a ceramic material and/or the like.

The particulate material may be provided in a mixture with a carrier medium, such as a fluid, gel and/or the like. In some examples a known quantity, such as a known weight of particulate material may be mixed with the carrier medium, such that following injection the known quantity will have be delivered into the flowline.

The injection apparatus may be used to inject a quantity, for example a known quantity, of particulate material into a flowline to be used in testing the operation of a particulate detector associated with the flowline, such as a sand detector. Thus, an aspect of the present disclosure relates to an injection apparatus for injecting a particulate material (e.g., sand) into a flowline (e.g., a well flowline) for use in testing the operation of a particulate (e.g., sand) detector operatively associated with the flowline. In one aspect, the injection apparatus may comprise a sand injector apparatus.

Where the injection medium is used in the testing of a detector, the injection medium may be defined as a testing medium.

In one example, by virtue of facilitating the testing of a particulate detector operatively coupled to the flowline, the operation may be defined as a field test.

Testing of the particulate detector may comprise validating or verifying output data from the particulate detector.

To facilitate testing of the particulate detector the particulate material may be injected upstream of the particulate detector. Testing of the particulate detector may comprise determining the accuracy of the detector, for example by virtue of injecting a known quantity of particulate material into the flowline. Testing of the particulate detector may comprise repeated injection of particulate material and determining the repeatability of the particulate detector. Testing of the particulate detector may comprise performing a calibration operation on the particulate detector. Where calibration is performed the injection medium may be defined as a calibration medium.

In use, the first chamber is filled with a desired volume of injection medium, which may be dictated by the particular operation, such as testing a flowline detector as noted above. In this respect where particulate material is to be injected a desired weight of particulate material may be mixed together with a carrier fluid (e.g., liquid, gel etc.) to provide the injection medium. A drive gas may be delivered and retained within the second chamber at a desired pressure. This desired pressure of the drive gas may be defined as a pre-set pressure.

The pressure of the drive gas may be selected to ensure that the piston may be driven a desired distance within the housing to displace a desired volume of the injection medium against the pressure of the flowline. The desired pressure of the drive gas may be determined in accordance with conventional gas law theory, for example using Boyle’s law concerning the relationship between gas volume and pressure at a constant temperature, based on equation (1) below:

PGB GB ⁼ PGA^GA (1) where PGB is the pressure of the drive gas before injection, VGB is the volume of the drive gas before injection, PGA is the pressure of the drive gas after injection, and VGA is the volume of the drive gas after injection. Rearranging to determine the pressure PGB of the drive gas before injection gives equation (2) below:

The total volume of the housing VH should be a known value, along with the required volume Vi of injection medium. As such, the volume VGB of the drive gas before injection can be approximated by equation (3) below:

V _GB = V _H - V _I (3)

Further, assuming that the drive gas occupies the total housing volume H after injection, and that the drive gas becomes pressure balanced with the flowline after injection, sufficient variables are known to calculate the desired initial drive gas pressure.

To provide an example, an injection volume of 2 litres from a 4 litre housing into a flowline at 20 bar will require a minimum drive gas pressure of 40 bar. As another example, an injection volume of 15 litres from a 25 litre housing into a flowline at 30 bar will require a minimum drive gas pressure of 75 bar. In some examples, however, additional initial gas pressure may be provided to ensure sufficient injection.

The drive gas may comprise any suitable gas, or mixture of gases, such as air, nitrogen, argon and/or the like. In applications where the flowline is used to communicate hydrocarbons therealong, any combustion supporting gases, such as air, may be avoided, with inert gases being preferred. The piston may be axially moveable within the housing. In such an arrangement the piston may define a linear piston. In alternative examples the piston may be arranged to move along an arcuate path. The piston may define a rotary piston.

The housing may comprise a housing bore, wherein the piston is mounted within the housing bore. The housing bore may be cylindrical. The housing bore may define the volume of the housing.

The housing may comprise a cylinder, for example provided by a tubular body. The housing may be formed of any suitable material, such as a metal or metal alloy, a composite material, a polymer and/or the like.

The piston may define a shape complimentary to a bore of the housing. The piston may comprise a disc piston. The piston may comprise a vane piston.

The piston may be configured for sliding engagement with an inner surface of the housing. The piston may comprise one or more bearing surfaces to facilitate sliding engagement.

The piston may be sealingly engaged with an inner surface of the housing to facilitate isolation between the first and second chambers. The piston may comprise a sealing arrangement for engaging the inner surface of the housing. By virtue of the required relative movement between the piston and the housing the sealing arrangement may define a dynamic sealing arrangement. When the injection outlet is closed any injection medium within the first chamber may be substantially pressure equalised with drive gas within the second chamber, such that any pressure differential across the piston may be minimised. When the injection outlet is open a pressure differential will be established across the piston, thus providing the driving force. Such a pressure differential may exist for a short period of time. As such, the pressure retaining requirements of the sealing arrangement may be provided accordingly.

The sealing arrangement may be bi-directional to ensure isolation of any pressure differential across the piston in reverse directions. In some examples interference between the piston and an inner surface of the housing may provide the sealing arrangement. Alternatively, or additionally, the sealing arrangement may comprise one or more sealing members, such as O-rings, chevron seal stacks, piston rings and/or the like.

The selectively openable injection outlet may comprise a valve to provide opening and closing of the injection outlet. The valve may be configured for manual operation, for example to be manually operated by a user. Such an arrangement may avoid any requirement for electrical power/control. In other examples, however, the valve may be power operated, for example electrically, hydraulically, pneumatically operated and/or the like. The valve may be configured for autonomous operation.

In some examples the selectively openable outlet may comprise a non-return valve.

The injection apparatus may comprise an injection medium inlet for permitting injection medium to be delivered into the first chamber. The injection medium inlet may be defined by the selectively openable injection outlet. Alternatively, the injection medium inlet may be defined separately from the selectively openable injection outlet.

The injection apparatus may comprise a drive gas inlet for permitting drive gas to be delivered into the second chamber and pressurised therein.

The injection apparatus may comprise one or more pressure gauges for identifying the pressure within one or both of the first and second chambers.

The injection apparatus may comprise a pressure relief arrangement for relieving pressure from the apparatus above a pressure threshold. Such a pressure relief arrangement may be operational to prevent over-pressurising the apparatus during charging with drive gas. Such a pressure relief arrangement may be operational to prevent the apparatus becoming over-pressurised following charging with pressurised drive gas, for example by increases in temperatures, as might be the case in locations with high ambient air temperatures. The pressure relief arrangement may be associated with one or both of the first and second chambers. In one example the pressure relief arrangement may be associated with the second chamber and may be arranged to vent pressurised gas beyond when the pressure threshold has been reached. The pressure relief arrangement may comprise one or more pressure relief valves.

The injection apparatus may comprise a volume indicator for determining the volume in one or both of the first and second chambers.

The injection apparatus may comprise a position indicator for determining the position of the piston within the housing. In one example knowledge of the position of the piston within the housing may permit the volume of one or both of the first and second chambers to be determined or estimated.

The position indicator may comprise a magnetic arrangement. For example, the piston may comprise a magnetic element configured to magnetically displace an indicator element provided externally (or at least externally visible) of the housing. In this respect the position of the indicator element may correspond to the position of the piston within the housing.

The apparatus may comprise an end closure at one or both ends of the housing, to provide a closed volume within the housing, wherein the piston is moveable within this closed volume.

The injection apparatus, in use, may be positioned adjacent the flowline. The injection apparatus may comprise a stand assembly, to permit appropriate self-support of the apparatus. In some examples the injection apparatus may be configured to be mounted on the flowline, for example via a clamping system, strap system etc.

The injection apparatus may be connected to an external wall of the flowline. The injection apparatus may be connected to an external surface of the flowline. The injection apparatus may be connected directly to the flowline. The injection apparatus may be connected indirectly to the flowline, e.g. via an intermediate structure.

The injection apparatus may be configured to be coupled to a manifold which is in communication with the flowline. In this respect the injection apparatus may be configured to be coupled to the manifold along with at least one other injection apparatus (which may or not be as defined herein), to provide increased volume of injection medium.

The injection apparatus may be provided as a pre-charged apparatus, comprising both the injection medium and pressurised drive gas contained therein and ready for use. In some examples, however, in the injection apparatus may be provided without any injection medium and/or driving gas, and thus configured to be charged as required, for example on location.

An aspect of the present disclosure relates to a method for injecting an injection medium into a flowline, comprising: providing an injection apparatus external to the flowline, the injection apparatus having a housing and a piston mounted therein to define a moving barrier between first and second chambers within the housing, wherein the first chamber contains the injection medium and the second chamber contains a pressurised driving gas; coupling an injection outlet of the first chamber to the flowline; and opening the injection outlet to permit pressurised driving gas in the second chamber to expand and drive the piston member in a direction to reduce the volume of the first chamber and eject at least a portion of the injection medium therefrom via the injection outlet and into the connected flowline.

The method may comprise using the injection apparatus of any other aspect, and thus all features defined in relation to the injection apparatus of any other aspect may also be considered for use in the present method.

The method may comprise injecting the injection medium into a well flowline, such as a production flowline, injection flowline, hydrocarbon flowline, and/or the like.

The method may comprise injecting any desired injection medium into a flowline, such as into a well flowline. The injection medium may comprise a fluid (including liquids, gases and mixtures thereof), a gel, a mixture, a solution, particulate material, a suspension, a solvent, and/or the like. The method may comprise injecting the injection medium into the flowline to perform a treatment function in the flowline, for example to the flowline itself (e.g., pipework) and/or to fluid flowing within the flowline.

The method may comprise injecting the injection medium into the flowline for subsequent detection at a location within the flowline, for example downstream of the point of injection into the flowline.

The method may comprise injecting an injection medium comprising a particulate material (e.g., a solid particulate material) into the flowline. In one example the method may comprise injecting sand into the flowline.

The method may comprise injecting a quantity, for example a known quantity, of particulate material into a flowline to be used in testing the operation of a particulate detector associated with the flowline, such as a sand detector.

The method may comprise filling the first chamber with a desired volume of injection medium, which may be dictated by the particular operation, such as testing a flowline detector as noted above. Where particulate material is to be injected the method may comprise mixing a desired weight of particulate material with a carrier fluid (e.g., liquid, gel etc.) to provide the injection medium, and then filling the first chamber with the injection medium.

The method may comprise delivering the drive gas into the second chamber at a desired pressure. This desired pressure of the drive gas may be defined as a pre-set pressure, or pre-charge.

The method may comprise determining the required drive gas pressure which ensures that the piston may be driven a desired distance within the housing to displace a desired volume of the injection medium against the pressure of the flowline. The desired pressure of the drive gas may be determined in accordance with the description provided above, for example.

An aspect of the present disclosure relates to a method for testing a particulate detector associated with a flowline, the method comprising: providing an injection apparatus having a housing and a piston mounted therein to define a moving barrier between first and second chambers within the housing, wherein the first chamber contains an injection medium comprising a particulate material and the second chamber contains a pressurised driving gas; coupling an injection outlet of the first chamber to the flowline upstream of the particulate detector; opening the injection outlet to permit pressurised driving gas in the second chamber to expand and drive the piston member in a direction to reduce the volume of the first chamber and eject at least a portion of the injection medium therefrom via the injection outlet and into the connected flowline; and detecting the injection medium with the particulate detector.

The method may comprise testing a sand detector. In this example the injection medium may comprise sand.

Testing of the particulate detector may comprise validating or verifying output data from the particulate data.

Testing of the particulate detector may comprise determining the accuracy of the detector, for example by virtue of injecting a known quantity of particulate material into the flowline. Testing of the particulate detector may comprise repeated injection of particulate material and determining the repeatability of the particulate detector. Testing of the particulate detector may comprise performing a calibration operation on the particulate detector. Where calibration is performed the injection medium may be defined as a calibration medium.

An aspect of the present disclosure relates to an injection apparatus for injecting a particulate material (e.g., sand) into a flowline (e.g., a well flowline) for use in testing the operation of a particulate (e.g., sand) detector operatively associated with the flowline, the injection apparatus comprising: a housing; a piston mounted in the housing and defining a moving barrier between first and second chambers within the housing, wherein the first chamber is for containing an injection medium comprising the particulate material and the second chamber is for containing a pressurised driving gas; and a selectively openable injection outlet in communication with the first chamber, wherein the injection outlet is connectable to the flowline, wherein, in use, the injection apparatus is external to the flowline, and when the injection outlet is opened pressurised driving gas in the second chamber is permitted to expand and drive the piston member in a direction to reduce the volume of the first chamber and eject injection medium therefrom via the injection outlet and into a connected flowline.

Thus, once injected the particulate material in the injection medium may be detected by the particulate detector with the data gathered used as part of a testing operation on the particulate detector, such as for validation, verification, calibration purposes and the like.

An aspect of the present disclosure relates to an injection apparatus configured to be coupled to a flowline, the injection apparatus configured to hold a particulate injection medium and a charge of compressed gas for use in displacing the particulate injection medium into the flowline.

An aspect of the present disclosure relates to a method for injecting an injection medium into a flowline, comprising: providing an injection apparatus containing the injection medium and a charge of compressed gas therein; coupling an injection outlet of the injection apparatus to the flowline; and displacing the injection medium from the injection apparatus using the compressed gas to cause the injection medium to be injected into the flowline.

An aspect of the present disclosure relates to a particulate detection system, comprising: a particulate detector for detecting sand flowing along a flowline; and an injection apparatus configured to be coupled to the flowline upstream of the particulate detector, wherein the injection apparatus is configured to hold a particulate injection medium and a charge of compressed gas for use in displacing the particulate injection medium into the flowline for use in testing the operation of the particulate detector.

The injection apparatus may be provided in accordance with any other aspect. It should be understood that features defined in relation to one aspect may be provided in combination with any other aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic illustration of a well-producing system, including an injection apparatus which is used to inject a quantity of sand into a flowline of the well-producing system;

Figure 2 is a perspective part sectional view of an example injection apparatus for injecting sand into a flowline;

Figure 3 is a perspective view of an injection apparatus mounted on an example support stand;

Figures 4 to 7 are diagrammatic illustrations of a sequence of charging the injection apparatus of Figure 2 in preparation for use;

Figures 8 and 9 are diagrammatic illustrations of the injection apparatus of Figure 2, in use, connected to a flowline;

Figure 10 is a diagrammatic illustration of several injection apparatuses connected together via a manifold to a flowline.

DETAILED DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure relate to apparatus and methods for injecting an injection medium into a flowline. Multiple applications may be possible and may facilitate injection of any injection medium into any flowline for any purpose. In some specific example applications the flowline may comprise a well flowline, into which it may be desirable to inject any desired injection medium, such as treatment chemicals, tracer elements and the like. However, for the purposes of providing an exemplary application the following description relates to an injection apparatus being used to inject a quantity of sand into a well flowline which accommodates the flow of fluids and material produced from a subterranean reservoir, for the purposes of testing a sand detector associated with the flowline.

Figure 1 diagrammatically illustrates an example well-producing system, generally identified by reference numeral 10. The system 10 includes a wellbore 12 which draws oil and/or gas from a subterranean reservoir 14, wherein the wellbore 12 is terminated at surface with a production wellhead 16. The production wellhead 16 may be at any location, such as subsea, topside, platform mounted, onshore and the like. A flowline 18 extends from the wellhead 16 to various processing and handling equipment and apparatus. For example, the flowline 18 may be in communication with a heater 20 and a separator 22 which functions to separate out the constituents of the produced fluids, including any oil, gas, water and solids, including sand particles. Any separated gas 28 may be directed through a flowline 24 to a scrubber 26 with clean gas then handled as required (e.g., collected, disposed of, such as back into the formation etc.). Any separated oil 32 may be directed through flowline 30 to be collected or refined. Any separated water 33 may be diverted through flowline 34 and subsequently treated, for example via floatation tanks 36, settling tanks 38 and filtration systems 40. The water may be disposed of (e.g., by over-boarding in an offshore environment), or may be injected back into the formation via injection equipment 42.

It may be beneficial to operators to have an understanding of the quantity of sand which is also flowing along the various flowlines, and for this purpose sand detectors may be used. In the present example a first sand detector 44 is associated with flowline 18 which delivers produced fluids from the wellhead 16, and a second sand detector 46 is positioned downstream of the separator 22, specifically associated with flowline 30 which carries separated oil 32. It should be recognised that any number of sand detectors may be positioned at any location within the system 10. Various types of sand detector are known, and may include acoustic detectors.

In some cases operators may require any sand detectors 44, 46 to be field tested, for example to validate or verify their produced data, their accuracy, repeatability and the like. Further, it may be necessary to calibrate or recalibrate any detectors 44, 46 from time-to-time. To facilitate such testing, one or more injection devices 50 may be coupled to the associated flowlines 18, 30, upstream of the respective sand detectors 44, 46 to be tested, and used to inject a quantity of sand or other particulate material into the associated flowlines 18, 30. This known quantity of sand can then provide a suitable test sample for the detectors 44, 46. In this respect, some operations may require the sand to be injected during steady state conditions, for example when the sand detectors 44, 46 in normal use provide a substantially uniform output. This may minimise the risk of the detectors 44, 46 also reading data from sand slugs produced from the formation 14 at the same time as the test sample is injected.

Figure 2 provides a partial cross-sectional view of the injection apparatus 50, diagrammatically illustrated in use with flowline 18 and sand detector 44. In this respect sand detector 44 may be of an acoustic type, and is illustrated as connected to a bent portion of the flowline 18. This particular arrangement may be used to permit the detector 44 to pick up individual collisions of entrained sand particles 52 with the internal wall of the flowline 18, with the collision rate used as one determination of sand quantity present within the flow. There are of course numerous other types of sand detector which could be used.

The injection apparatus 50 comprises a cylindrical housing 54 which defines a cylindrical bore 56. A disc piston 58 is mounted within the cylindrical bore 56 of the housing 54 and defines a moving barrier between first and second housing chambers 60, 62. The first chamber 60 contains a desired volume of injection medium (e.g., sand particles in a fluid and/or gel mixture or slurry), whereas the second chamber 62 contains a pressurised/compressed drive gas.

The injection apparatus 50 further includes an injection outlet 64 which in this example is controlled by a manually operated valve 66. A hose or other conduit 67 provides a connection between the valve 66/injection outlet 64 and the flowline 18, upstream of the detector 44. When the valve 66 is opened the drive gas in the second chamber 62 is permitted to expand and drive the disc piston 58 in the direction of arrow 68 to reduce the volume of the first chamber 60 and eject the injection medium through the injection outlet 64 and into the flowline 18 via connected hose 67. As noted above, the quantity of sand contained in the injection medium may be used as a known test sample for the detector 44.

The injection apparatus 50 further comprise a gas inlet valve 70 which facilitates charging and retention of the drive gas into the second chamber 62. The injection apparatus 50 further comprises a position indicator 72 which permits an operator to determine the position of the piston 58 within the housing 54. Knowledge of the position of the piston 58 may permit the volume of the injection medium in the first chamber 60 to be determined or estimated. In the present example the position indicator 72 comprises a magnet 74 secured to the piston 58 and a magnetic indicator follower 76 located externally of the housing 54 (or at least visible externally of the housing 54), such that the indicator follower 76 reflects the position of the piston 58. Other position indicators may alternatively or additionally be used.

The injection apparatus 50 is positioned external to the flowline 18. For example, the injection apparatus 50 may be suitably mounted adjacent or on the flowline 18. In some examples the injection apparatus 50 may be secured to the flowline, for example via a clamping system, strap system, or the like. In other examples, as illustrated in Figure 3, the injection apparatus may be mounted on a stand 78, such as a tripod.

Figure 3 also illustrates an optional feature of the use of one or more pressure gauges 80 which may provide an operator with an indication of the pressure in one or both of the first and second chambers 60, 62 (Figure 2).

A sequence of filling, or charging, the injection apparatus 50 will now be described with reference to the diagrammatic sequence drawings of Figures 4 to 7.

An empty injection apparatus 50 is shown in Figure 4, with the piston 58 positioned in the housing 54 such that the volume of the first chamber 60 is at a minimum and the volume of the second chamber 62 is at a maximum. As shown in Figure 5, an injection medium 82 (e.g., sand particles and a fluid and/or gel carrier or slurry) is flowed into the first chamber 60 via an injection medium inlet 84. In this example the first chamber 60 is overfilled with injection medium 82. Following this, as illustrated in Figure 6, gas inlet valve 70 is maintained open and drive gas 86 (e.g., nitrogen) is driven into the second chamber 62, with the piston 58 being driven in a direction to displace the injection medium 82 back through its inlet 84 which remains open. This movement of the piston 58 is permitted until the desired volume of injection medium 82 remains in the second chamber, as derived from the piston position indicator 72, at which point the injection fluid inlet 84 is closed, as illustrated in Figure 7. Gas may then continue to be driven into the second chamber 62 until the desired gas pressure is reached, for example as indicated by pressure gauge 80. The injection apparatus 50 may optionally comprise a pressure relief valve, as shown in Figure 7, which may function to prevent overpressurising the second chamber 62. Such over-pressure protection may be provided at the point of charging, or alternatively may provide protection in the event of pressure increases due to increases in temperature.

Once appropriately charged and on-site, the injection apparatus 50 is coupled to a flowline 18, as shown in Figure 8. The injection outlet valve 66 may then be opened, as illustrated in Figure 9, permitting the compressed drive gas 86 to expand in the second chamber 62 and drive the piston 58 in a direction to eject the injection medium 82 from the first chamber 60 and into the flowline 18.

In the example provided above the required pressure of the drive gas is predetermined such that sufficient volume of injection medium 82 may be displaced from the first chamber 60 against the flowline pressure. This determination of gas pressure may be performed in accordance with gas laws, such as described hereinbefore.

In some examples a larger volume of injection medium 82 may be provided by increasing the size of the housing 54, and/or permitting a larger initial volume of the first chamber 60 by using a higher drive gas pressure. However, in other examples, as illustrated in Figure 10, additional injection medium volume may be achieved by connecting multiple injection apparatuses 50a, 50b, 50c (and more or less if required) together via an injection manifold 90.

It should be understood that the examples provided herein are only presented to exemplify the present disclosure, and that various variations within the scope of the present disclosure is possible. For example, the injection apparatus disclosed may be used to inject any medium into any flowline.