GB2546100A

GB2546100A - Wellhead control system

Info

Publication number: GB2546100A
Application number: GB1600340.2A
Authority: GB
Inventors: Bell Robert
Original assignee: GE Oil and Gas UK Ltd
Current assignee: Baker Hughes Energy Technology UK Ltd
Priority date: 2016-01-08
Filing date: 2016-01-08
Publication date: 2017-07-12
Also published as: WO2017118579A1; GB201600340D0

Abstract

A pressure control system 10 for an oil or gas well, comprising: a moveable member 105 moveable between an open configuration in which fluid is permitted to flow from a first region of the well 101 to a second region of the well 102, through passageway 108 and a closed configuration in which fluid flow from the first region to the second region is prevented, inlet 109 may be blocked; a biasing member 110, which may be a spring, configured to urge the moveable member towards the closed configuration; and a pressure controller, wherein the pressure controller is arranged to control a pressure that acts on the moveable member to urge the moveable member towards the closed configuration. The pressure controller may include a pressure sensor 103 and an isolation valve 104. There may also be a third closed configuration. Also claimed is an assembly comprising two pressure control systems 10 and also an oil or gas well comprising the pressure control system 10.

Description

Wellhead Control System

The present invention relates to a pressure control system. More particularly the present invention provides a pressure control system for an oil or gas well.

Oil and gas are typically extracted from beneath the Earth’s surface by wells. Such wells are typically constructed by drilling a wellbore deep into the ground. A number of concentrically aligned tubular pipes, known as tubings or casings, are installed within the wellbore which penetrate to different depths below ground in order to facilitate the extraction of oil and gas from hydrocarbon producing formations of the Earth’s crust. An annular gap is formed between each layer of the casings, each annulus typically containing pressurised fluid which remains within the annulus as a remnant of the drilling process. The central casing is typically known as a production tubing and is used to channel extracted oil from the well to the Earth’s surface. The casings are typically secured to one another via a casing hanger located at a top portion of the well, referred to as a wellhead. A treehead is mounted above the wellhead, and typically contains an assembly of valves and pipes which regulate the flow of oil and gas from the well and the pressure of the fluid within each annulus.

The casings are subjected to high external pressures caused by the weight of the Earth’s crust pressing on the casings, and therefore the fluid pressures within the annuli are typically regulated to maintain the pressure at or close to the pressure exerted on the casings by the Earth in order to prevent collapse or rupture of the tubes. Furthermore, leakage of fluid between the annuli and/or thermal expansion of the fluids within the annuli may cause the pressure in the annuli to increase, which may cause damage to the well casings, the wellhead, or the components of the treehead.

One way of controlling fluid pressure in the annuli is to provide a sacrificial member configured to mechanically rupture once the pressure of the fluid within a particular annulus rises above a rated pressure of the sacrificial member. Such an arrangement is commonly known as a burst disk, and is typically formed by providing a vent path from the annulus in question, often in the form of a conduit of the treehead, and providing a barrier within the vent path, often in the form of a metal disk or diaphragm, to prevent flow of fluid along the vent path. When the pressure in the annulus increases, the barrier deforms in response to the increasing pressure until the barrier mechanically ruptures, thus allowing fluid to vent from the annulus. The pressure within the annulus is thus relieved, and the vented fluid can be channelled away from the well via the treehead conduit. Typically, valves are provided within the treehead to regulate the flow of the vented fluid.

According to a first aspect of the invention, there is provided a pressure control system for an oil or gas well, comprising: a moveable member moveable between an open configuration in which fluid is permitted to flow from a first region of the well to a second region of the well and a closed configuration in which fluid flow from the first region to the second region is prevented; a biasing member configured to urge the moveable member towards the closed configuration; and a pressure controller, wherein the pressure controller is arranged to control a pressure that acts on the moveable member to urge the moveable member towards the closed configuration. The pressure that acts on the moveable member to urge the moveable member towards the closed configuration may also act to urge the moveable member towards a state of venting. A property of the biasing member may be selected based upon the pressure that acts on the moveable member to urge the moveable member towards the closed configuration. The property of the biasing member may be a size of the biasing member, such as an axial length of the biasing member or a width or a diameter of the biasing member. The property of the biasing member may also be a type of biasing member, such as the material of the biasing member or the spring constant of the biasing member. In general, the property of the biasing member may be any factor that may vary the force applied by the biasing member.

The moveable member may be moveable within a cavity fluidly connected to the first region and the second region. The moveable member may be configured to selectively permit fluid flow from the first region to the second region via a flow passage fluidly connecting the first region to the second region. The moveable member may be configured to substantially cover a first opening of the flow passage when the moveable member is in the closed configuration such that fluid flow communication between the first opening and the first region is substantially prevented. The first opening may be in fluid flow communication with the first region when the moveable member is in the open configuration. The first opening of the fluid flow passage may be an opening of the cavity.

The moveable member may be arranged such that in use a pressure acts upon the moveable member to urge the moveable member towards the open configuration. For example, the pressure which acts upon the moveable member to urge the moveable member towards the open configuration may be a pressure associated with the first region.

The pressure controller may be arranged to control the pressure that acts on the moveable member to urge the moveable member towards the closed configuration based upon the pressure that acts upon the moveable member to urge the moveable member towards the open configuration. For example, the pressure that acts upon the moveable member to urge the moveable member towards the open configuration may typically have a known value and the pressure controller may base the pressure upon the known value.

For example the pressure that is controlled by the pressure controller may be controlled such that the force resulting from the pressure that urges the moveable member towards the closed configuration is smaller than the force that urges the moveable member towards the open configuration. It will be appreciated that the pressure that acts to urge the moveable member towards the closed configuration and the pressure that acts to urge the moveable member towards the open configuration generally act in substantially opposite directions. As such, the pressures act against one another such that a net force is produced upon the moveable member that acts to urge the moveable member towards the open configuration. The biasing member may be configured to urge the moveable member towards the closed configuration such that in normal operation of the pressure control system the moveable member is in the closed configuration, however where the pressure that acts to urge the moveable member towards the open configuration increases, the moveable member is moved towards the open configuration. As such, the size and/or type of biasing member may be selected based upon the magnitude of the net force provided by the pressures.

The pressure that acts upon the moveable member to urge the moveable member towards the closed configuration may be associated with the second region. The pressure in the second region may be controlled by the controller.

The moveable member may be moveable to a further closed configuration in which fluid flow from the first region to the second region is prevented when the pressure that acts on the moveable member to urge the moveable member towards the closed configuration is below a predetermined threshold. The open configuration may therefore be an intermediate position between two closed configurations. That is, under normal operating conditions, when the pressure in the first region is below a predetermined threshold the moveable member will be in the closed configuration, and when the pressure in the first region is above the predetermined threshold the moveable member will be in the open configuration. In exceptional operating conditions, such as when no pressure is applied by the controller (for example when the pressure controller is removed) or when a smaller pressure than normal operation pressure is applied by the controller, the moveable member may move to a further closed configuration.

It will be appreciated that the pressure control system may define an operating sequence in which the moveable member is moveable from the closed configuration to the open configuration, and from the open configuration to the further closed configuration. When the moveable member is in the closed configuration fluid flow from the first fluid region to the second fluid region is substantially prevented. When the moveable member is in the open configuration fluid flow from the first fluid region to the second fluid region is permitted. When the moveable member is in the further closed configuration fluid flow from the first fluid region to the second fluid region is substantially prevented. The moveable member may move between the closed configuration and the open configuration depending upon the force applied to the moveable member by the pressure in the first fluid region, the biasing member, and the pressure in the second fluid region. The moveable member will move to the further closed configuration when the pressure in the first fluid region exceeds the pressure in the second fluid region by a substantial amount or when the moveable member is no longer urged by the pressure in the second fluid region. For example, the moveable member will move to the further closed configuration when the pressure in the second fluid region is zero or near-zero. As such, the moveable member may move to the further closed configuration when a treehead of the oil or gas well is removed from the well.

The moveable member may be configured to substantially cover a second opening of the flow passage when the moveable member is in the further closed configuration. The second opening of the flow passage may be an opening of the cavity. A distance between the first opening and the second opening may be configured based upon a size of the moveable member. The first opening and the second opening may be spaced apart such that when the moveable member is in the open configuration, the first opening is in fluid flow communication with the first region and the second opening is in fluid flow communication with the second region. The first opening may be in fluid flow communication with the first fluid region when the moveable member is in either of the open configuration or the further closed configuration. The second opening may be in fluid flow communication with the second region when the moveable member is in either of the open configuration or the closed configuration. The moveable member, first opening and second opening may therefore be arranged such that the moveable member operates to block fluid flow in two configurations in which one of the first or second openings is covered by the moveable member, and to allow fluid flow in a further configuration in which both of the first and second openings are uncovered by the moveable member.

The first region may be in fluid flow communication with an annulus of the oil or gas well. In particular, the first region may be in fluid flow communication with an annulus B of the oil or gas well.

The pressure control system may further comprise a pressure sensor arranged to determine a pressure of the second region. It will be appreciated that the pressure sensor may sense the pressure in a region that is controlled by the pressure controller as part of a feedback loop of the controller. The sensor and pressure controller may therefore operate to control the pressure of the second region.

The pressure control system may further comprise an isolation valve configured to selectively permit fluid flow from the second region to an environment external to the well. The pressure controller may communicate with the isolation valve to selectively actuate the isolation valve. For example, the pressure controller may selectively actuate the isolation valve based upon a pressure sensed by the pressure sensor.

The biasing member may be a spring. For example, the biasing member may be for example a compression spring, a tension spring, a torsion spring or a leaf spring.

The pressure control system may comprise a further arrangement of a moveable member, a biasing member, a cavity and a flow passage so as to provide an arrangement comprising two pressure control systems. In particular there may be provided an assembly for controlling pressure comprising: a first pressure control system according to any preceding claim; and a second pressure control system according to any preceding claim; wherein a first biasing member of the first pressure control system is configured to permit the first moveable member to move to the open configuration at a first threshold pressure of the first region and a second biasing member of the second pressure control system is configured to permit the second moveable member to move to the open configuration at a second threshold pressure of the first region.

That is, the moveable member described above may be a first moveable member and the biasing member may be a first biasing member; and wherein the pressure control system may further comprise: a second moveable member moveable to an open configuration in which fluid is permitted to flow from the first region of the well to the second region of the well and a closed configuration in which the second moveable member prevents fluid flow from the first region to the second region; and a second biasing member configured to urge the second moveable member towards the closed configuration; and the first biasing member may be configured to permit the first moveable member to move to the open configuration at a first threshold pressure of the first region and the second biasing member may be configured to permit the second moveable member to move to the open configuration at a second threshold pressure of the first region.

It will be appreciated that the first moveable member and the first biasing member may define a first shuttle valve assembly, and the second moveable member and the second biasing member may define a second shuttle valve assembly. The first threshold pressure may be determined by the mechanical properties and/or the geometry of the first biasing member, and the second threshold pressure may be determined by the mechanical properties and/or the geometry of the second biasing member. In particular, one of the first or second biasing members may be configured to deflect further than the other of the first or second biasing members under the same force. The first and second moveable members may be urged towards their respective open configurations due to the pressure of the fluid in the first fluid region. As such, said one of the first or second biasing members may permit their respective first or second moveable members to move to the open configuration under the action of a lower pressure in the first region than that required to move the other of the first or second moveable members to their respective open configuration.

According to a second aspect of the invention there is provided an oil or gas well comprising: a wellbore; a first tubular member contained within the wellbore; a second tubular member circumferentially surrounding at least a portion of the first tubular member to define a spacing between the first tubular member and the second tubular member and within which a fluid is contained; and a pressure control system according to the first aspect of the invention arranged to fluidly communicate with the fluid contained within the spacing.

Specific embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic side view of a well;

Figure 2 is an enlarged schematic cross-sectional side view of a portion of a well incorporating a pressure control system according to the present invention;

Figure 3 is a schematic view of an example isolation valve control system for use with the present invention;

Figure 4 is a schematic view of a closed configuration of a pressure control system for a well according to a first embodiment of the present invention;

Figure 5 is a schematic view of an open configuration of a pressure control system for a well according to the first embodiment of the present invention;

Figure 6 is a schematic view of a closed configuration of a pressure control system for a well according to a second embodiment of the present invention;

Figure 7 is a schematic view of an open configuration of a pressure control system for a well according to the second embodiment of the present invention;

Figure 8 is a schematic view of a deadlock configuration of a pressure control system for a well according to the second embodiment of the present invention; and

Figure 9 is a schematic view of a third embodiment of a pressure control system according to the present invention.

This written description uses examples to disclose the invention, including the preferred embodiments, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. Aspects from the various embodiments described, as well as other known equivalents for each such aspects, can be mixed and matched by one of ordinary skill in the art to construct additional embodiments and techniques in accordance with principles of this application.

Figure 1 is a schematic cross-section of a side view of a well. In particular, Figure 1 shows a well 1 located on a surface 2 of the Earth’s crust. The well 1 may be located on land or may be located underwater, in which case the surface 2 is a seabed. The well 1 comprises a wellbore containing a production tubing 3, an intermediate casing 4 and an outer casing 5. The production tubing 3 and casings 4, 5 are each formed as a substantially tubular member having a hollow central portion through which fluid may flow. The production tubing 3 has an outer diameter which is smaller than an inner diameter of the intermediate casing 4 so as to form an annular gap A. Similarly, the intermediate casing 4 has an outer diameter which is narrower than an inner diameter of the outer casing 5 so as to form an annular gap B. The production tubing 3, intermediate casing 4, and outer casing 5 are connected at a wellhead 6 located at the surface 2. The tubing 3 and/or casings 4, 5 typically comprise a hanger portion (not shown) located at an end of the tubing 3 and/or casings 4, 5 closest to the surface 2, which is received within the wellhead 6 so as to secure the tubing 3 and/or casings 4, 5 to the wellhead 6 and to allow the tubing 3 and/or casings 4, 5 to hang within the well 1. A treehead 7 is located above the wellhead 6 and is connected to a pipeline 8.

The production tubing 3 penetrates a formation 9 of the Earth’s crust containing oil and/or gas for extraction. The extracted oil and/or gas, sometimes referred to as production fluid, is channelled to the surface 2 via the central portion of the production tubing 3. The production fluid may rise from the formation 9 to the surface 2 via the production tubing 3 under the action of pressure applied by the Earth on the formation 9, or may be extracted from the well 1 via a pump (not shown). At the surface 2, the production fluid passes through the wellhead 6 and into the treehead 7. The treehead 7 is arranged to regulate the flow of the production fluid, and to channel the production fluid out of the well 1 via the pipeline 8. The production fluid is then carried away from the well by the pipeline 8 for storage or processing down-stream (not shown).

It will be appreciated that whilst the present invention is described in the context of a well 1 comprising a treehead 7, the well 1 may comprise a different pressure containing or controlling device which is functionally equivalent to the treehead, such as for example a blow-out preventer or a pressure control cap. It will further be appreciated that the treehead 7 may be either a vertical-type treehead or a horizontal-type treehead.

Each annulus A, B contains fluid which is typically a by-product of the well-drilling process. As such, the annulus fluid may be a drilling fluid, for example: air, water, water-based mud, oil-based mud, synthetic drilling fluid or a mixture of these. Alternatively, the fluid in each annulus may be injected into the annulus separately from the well-drilling process. The pressure of the fluid in annulus A or annulus B may increase due to one or more of leakage of fluid between annulus A and annulus B, leakage of production fluid from the production tubing to annulus A or annulus B, thermal expansion of the fluid within either annulus A or annulus B. It will be appreciated that it is desirable to regulate the pressure of the fluid contained within each annulus A, B to maintain the fluid pressure at an appropriate value. Fluid pressure which is too low may result in collapse of the casings 3, 4, 5, whilst fluid pressure which is too high may cause rupture of or damage to the casings 3, 4, 5, the wellhead 6 or the components of the treehead 7.

Figure 2 shows a schematic cross-sectional side view of a portion of a wellhead. In particular Figure 2 shows a hanger portion 401 of the intermediate casing 4 which is in contact with a wellhead housing 601 of the wellhead 6. The wellhead housing 601 is formed as a generally hollow cylinder sized to surround the production tubing 3, intermediate casing 4, and outer casing 5. The hanger portion 401 is a top portion of the intermediate casing 4 configured to connect the intermediate casing 4 to the wellhead housing 601 and as such allow the intermediate casing 4 to hang from the wellhead 6 within the well 1. The hanger portion 401 may be integrally formed with the intermediate casing 4 or may be a separate component to the intermediate casing 4 to which the intermediate casing 4 is attached. The hanger portion 401 comprises a support mechanism 402 configured to contact the wellhead housing 601 and enclose the annulus B such that fluid within the annulus is prevented from escaping. The treehead 7 is mounted above the wellhead 6, and is connected to the intermediate casing 4 via an isolation sleeve 701.

The outer casing 5 contacts the wellhead housing 601 in a similar manner as the intermediate casing 4 at a location below the hanger portion 401. As such, the annulus B is partially formed between an inner diameter of the outer casing 5 and an outer diameter of the intermediate casing 4, and partially formed between an inner diameter of the wellhead housing 601 and an outer diameter of the intermediate casing 4 or hanger portion 401. Although not shown, it will be appreciated that the wellhead housing 601 may comprise features such as steps, ridges or chamfers which are configured to mate with corresponding features of the hanger portion 401 in order to secure the hanger portion 401 to the wellhead casing 601. In particular, such features may allow the intermediate casing 4 to hang from the wellhead housing 601 via the hanger portion 401. In an alternative embodiment, the wellhead housing 601 may not be present and the hanger portion 401 may contact an inner surface of the outer casing 5 in a similar manner to that described above between the hanger portion 401 and the wellhead housing 601. It will be appreciated that where the treehead 7 is a horizontal-type treehead, the production tubing 3 may hang from a hanger portion of the treehead 7, rather than from the wellhead housing 601.

Figure 2 further shows a pressure control system 10, located partially within the hanger portion 401 of the intermediate casing 4 and partially within the treehead 7. The pressure control system 10 comprises a shuttle valve 100 connected to the annulus B via an inlet conduit 101 and to the isolation sleeve 701 via a first portion 102a of an outlet conduit 102. The first portion of the outlet conduit 102a connects to a corresponding second portion 102b of the outlet conduit 102 formed within the isolation sleeve 701. The outlet conduit 102b is fluidly connected to a pressure sensor 103 and to an isolation valve 104 of the treehead 7. The shuttle valve 100 is configured to selectively permit fluid to flow from the annulus B through the inlet conduit 101 and into the first portion of the outlet conduit 102a. The fluid then passes to the second portion of the outlet conduit 102b, and the increase in fluid pressure is sensed by pressure sensor 103. The isolation valve 104 may be opened in response to the increase in pressure, and fluid within the outlet conduit 102b may be vented from the treehead 7 via the isolation valve 104 to restore the pressure within outlet conduit 102b to a required pressure.

It will be appreciated that although the components of the pressure control system 10 (such as the inlet conduit 101, the shuttle valve 100, and the outlet conduit 102) are located partially within the hanger portion 401, isolation sleeve 701 and treehead 7, some components of the pressure control system 10 may alternatively be located elsewhere within the well 1. For example, the pressure control system 10 may be located at least partially within a hanger portion of the outer casing 5, or within the wellhead casing 601. The pressure control system 10 may be formed as a separate and distinct part of the well 1 to the production tubing 3, casings 4, 5, wellhead 6 and treehead 7.

The pressure sensor 103 and isolation valve 104 together maintain the pressure in the outlet conduit 102a, 102b at or close to a target pressure by selectively venting fluid from the outlet conduit 102a, 102b via the isolation valve 104. An example of a pressure controller configured to control the actuation of the valve 104 is shown schematically in Figure 3, although it will be appreciated that alternative configurations of such pressure controller may be used in conjunction with the pressure control system 10. A control module 120 is arranged in electrical communication with the pressure sensor 103 which is operable to measure the pressure of the fluid within an outlet conduit 102. It will be appreciated that the outlet conduit 102 corresponds to the first and second portions of the outlet conduit 102a, 102b in Figure 2. An electric motor 121 is in electrical communication with the control module 120 and is mechanically coupled to the isolation valve 104 such that the electric motor 121 is operable to selectively open and close the isolation valve 104 either wholly or partially.

The pressure of the fluid within the conduit 102 is communicated to the control module 120 where it is compared against a pre-determined target pressure. If the sensed pressure exceeds the target pressure, the control module causes the isolation valve 104 to open. The pressure sensor 103 detects when the pressure within the conduit 102 drops to the target pressure, and the control module 102 causes the isolation valve 104 to close. As such, fluid pressure within the outlet conduit 102 can be maintained at or close to the target pressure. It will be appreciated that although actuation of the isolation valve 104 is described in the context of an electrical valve control system, actuation of the isolation valve 104 may be controlled in any suitable manner. For example, the isolation valve 104 may be a hydraulically-actuated valve actuated by a hydraulic control system in response to a pressure reading from the pressure sensor 103.

Figures 4 and 5 show a schematic view of a pressure control system 10 according to an embodiment of the present invention. The shuttle valve 100 comprises a moveable member 105 configured to move within a cavity 106 in the direction of a longitudinal axis of the cavity. The cavity 106 and moveable member 105 are of like cross-sections relative to the longitudinal axis of the cavity 106 and are sized such that minimal spacing exists between the moveable member 105 and the cavity 106 whilst permitting slideable movement of the moveable member 105 within the cavity 106. Sealing members 107, for example in the form of o-rings, v-rings or piston rings, may be connected to the moveable member 105 and may act to substantially prevent the passage of fluid through the spacing between the moveable member 105 and the cavity 106. It will be appreciated that the cavity 106 and moveable member 105 may have any substantially constant cross-section with respect to the longitudinal axis. For example, the movable member may be cylindrical and the cavity may be formed of a corresponding cylindrical void.

The inlet conduit 101 is fluidly connected to the cavity 106 by an inlet 112 such that the cavity 106 is in fluid flow communication with the annulus B (not shown) on a first side of the moveable member 105 to form a first fluid region. The outlet conduit 102 is fluidly connected to the cavity 106 via an outlet 113 on a second side of the moveable member 105 to form a second fluid region. The inlet 112 and the outlet 113 are arranged on substantially opposite sides of the moveable member 105 such that the first and second fluid regions are located on respective substantially opposite sides of the moveable member 105. The respective substantially opposite sides of the moveable member 105 may be generally normal to the longitudinal axis of the cavity.

According to the embodiment depicted in Figure 4, the inlet 112 and outlet 113 are located at substantially opposite end faces of the cavity 106, however, it will be appreciated that the inlet 112 and outlet 113 may be connected to the cavity 106 via a side wall of the cavity 106. It will further be appreciated that the outlet conduit 102 is equivalent to the outlet conduits 102a and 102b depicted in Figure 2. As such, the outlet conduit 102 may be partially formed by the hanger portion 401 and partially formed by the treehead 7.

The shuttle valve 100 further comprises a fluid flow passage 108 connected to the cavity 106 via an opening 109 located at a first end of the fluid flow passage 108, and further connected to the outlet conduit 102 at a second substantially opposite end of the fluid flow passage 108.

The moveable member 105 is moveable within the cavity 106 between a closed configuration and an open configuration. When the moveable member 105 is in the closed configuration, such as that shown in Figure 4, fluid flow from the first fluid region to the fluid flow passage 108 is substantially prevented by the moveable member 105 substantially covering the opening 109. In the embodiment of Figure 4 the opening 109 is positioned on a side wall of the cavity 106. It will be appreciated that in alternative embodiments the opening 109 may be positioned elsewhere, such as for example on a bottom face of the cavity 106 (i.e. adjacent the inlet 112). When the moveable member 105 is in the open configuration, such as that shown in Figure 5, the moveable member 105 is displaced along the longitudinal axis such that the opening 109 is no longer covered and fluid in the first fluid region may pass into the fluid flow passage 108. A biasing member 110 is mounted within the cavity 106 and is configured to urge the movable member 105 towards the closed configuration. The biasing member 110 is typically provided in the form of a compression spring located above the moveable member 105 and is arranged to urge the moveable member 105 along the longitudinal axis of the cavity towards the closed configuration. However, it will be appreciated that the biasing member 110 may alternatively be provided in the form of a tension spring configured to pull, rather than push, the moveable member 105 towards the closed configuration. Furthermore, the biasing member 110 may be provided in the form of any other resiliently deformable member, such as, for example, a leaf spring or a torsion spring.

The isolation valve 104 and pressure sensor 103 are configured to set and maintain a pressure P2 of the fluid in the second fluid region at a target value. The pressure P2 is set based upon a pressure P1 of the fluid in the first fluid region (which it will be appreciated is substantially the same as the pressure within the annulus B) and the force exerted by the biasing member 110 on the moveable member in the direction of the closed configuration, such that when the pressure within the annulus B is at or below a predetermined threshold pressure, the moveable member 105 is maintained in the closed configuration by the action of the biasing member 110 and the pressure P2.

In more detail, the pressure P1 of the fluid in the first fluid region acts upon a bottom face of the moveable member 105 to urge the moveable member 105 towards the open configuration. The force exerted upon the moveable member 105 towards the open configuration is equal to the product of the pressure P1 and the cross-sectional area A of the moveable member 105 relative to the direction of movement of the moveable member 105.

Fopen = Pi A

Likewise the pressure P2 of the fluid in the second fluid region acts upon a top face of the moveable member 105 to urge the moveable member 105 towards the closed configuration. The force exerted upon the moveable member 105 towards the closed configuration by the fluid in the second fluid region is equal to the product of the pressure P2 and the cross-sectional area A of the moveable member 105 relative to the direction of movement of the moveable member 105. Furthermore, the biasing member 110 also acts to urge the moveable member 105 towards the closed configuration and exerts a force which is equal to the product of the spring constant k of the biasing member 110 and the distance xby which the biasing member 110 has been compressed. As such, the total force exerted on the moveable member 105 which acts to urge the moveable member 105 towards the closed configuration is given by: T'close

It will be appreciated that because the pressure P2 in the second fluid region is maintained at a near-constant pressure by the control module 120 (in conjunction with the pressure sensor 103 and isolation valve 104), the resultant force produced upon the moveable member 105 by the fluid in the second fluid region remains approximately constant. However, an increase in the pressure of the fluid within annulus B (i.e. an increase in the pressure P1) will cause a corresponding increase in the resultant force applied to the moveable member 105 by the first fluid region, and so the moveable member 105 will be displaced in the direction of the open configuration and the biasing member 110 compressed. It will be appreciated that as the biasing member 110 is compressed, the resultant force produced by the biasing member 110 upon the moveable member 105 increases in proportion to the displacement x of the moveable member 105. The displacement x of the moveable member 105 is therefore proportional to the pressure of the fluid in the annulus B.

When the pressure P1 increases above the predetermined threshold pressure, the moveable member 105 is displaced in the direction of the open configuration such that at least a portion of the opening 109 is exposed to the fluid in the first fluid region. A portion of the fluid within the first fluid region, being at a higher pressure than the fluid in the second fluid region, may then pass into the second fluid region via the fluid flow passage 108 and the opening 109. It will be appreciated that the difference in pressure between the fluid in the first fluid region and the fluid in the second fluid region drives the flow of fluid from the first fluid region to the second fluid region along the fluid flow passage 108. Because the first fluid region and the annulus B are connected by the inlet conduit 101, fluid from the annulus B may be vented into the outlet conduit 102 via the fluid flow passage 108 when the moveable member 105 is in the open configuration (as shown in Figure 5). It will be appreciated that as the fluid from the first fluid region vents into the outlet conduit 102, the pressure in the first fluid region, and in turn the pressure of the fluid in annulus B, decreases. As such, the resultant force acting on the moveable member 105 (caused by the pressure P1) which acts to move the moveable member 105 towards the open configuration decreases proportionally. As the pressure P1 decreases, the biasing member 110 is able to overcome the resultant force caused by P1 and the moveable member 105 therefore returns to the closed configuration, thus preventing fluid passing through the opening 109.

The threshold pressure may be determined based upon a pressure rating of the wellhead 6 and a safety margin. The pressure rating of wellhead 6 is typically within the range of 3 - 13 kpsi (20.7 - 89.6 MPa) and the safety margin is typically about 2 kpsi (13.7 MPa). For example, the pressure rating of the wellhead 6 may be 5 kpsi (34.4 MPa) and the threshold pressure may therefore be set at 3 kpsi (20.7 MPa) so as to provide a 2 kpsi (13.7 MPa) safety margin. It will be appreciated that the pressure rating of the wellhead 6 may be dependent upon the strength and/or the capability of the wellhead 6. It will be appreciated that the pressure P2 is determined based upon the threshold pressure and a pressure value equivalent to the force applied to the moveable member 105 by the biasing member 110 when the moveable member 105 is in the open configuration. For example, the force applied to the moveable member 105 by the biasing member 110 when the moveable member 105 is in the open configuration may be equivalent to a pressure differential of 200 psi (1.38 MPa), and therefore the pressure P2 may be set at 2.8 kpsi (19.3 MPa).

It will be appreciated that the fluid vented from annulus B will cause a corresponding increase in the pressure of the fluid in the outlet conduit 102, however this increase in pressure is regulated by the control module 120 such that the pressure P2 remains approximately constant.

It will be appreciated that when the moveable member is in the open position the resultant force acting on the moveable member 105 by the pressure P1 is greater than both the resultant force acting on the moveable member 105 due to the pressure P2 and the force produced by the biasing member 110. As such, when the moveable member is in the open position the pressure P1 is greater than the pressure P2. As such, backflow of fluid from the second fluid region to the first fluid region is prevented.

The biasing member 110 may be configured to be at least partially compressed when the moveable member 105 is in the closed configuration, such that the biasing member 110 always exerts a force upon the moveable member. Alternatively, the biasing member 110 may be configured to be uncompressed when the moveable member 105 is in the closed configuration, such that the biasing member 110 only exerts a force on the movable member 105 once the moveable member 105 is displaced.

It will be appreciated that whilst the threshold pressure required to urge the moveable member 105 to the open configuration is substantially dependent upon the pressure P2 controlled by the isolation valve 104, the geometry and materials of the shuttle valve 100 may also affect the threshold pressure. In particular the threshold pressure may be dependent upon: the material properties of the biasing member 110 (in particular the spring constant A); the dimensions of the moveable member 105 (in particular the cross-sectional area A); and the position of the opening 109 relative to the uncompressed dimensions of the biasing member 110 (in particular the displacement x). It will be appreciated that the precise value of each of these properties may vary depending upon the set-up of the particular well 1, however the values are chosen such that once the pressure P1 reaches the threshold pressure, the moveable member 105 will allow fluid flow through the opening 109. It will be appreciated that the target pressure set by the control module 120 may be set based upon, in particular: the depth of the well 1; pressure exerted by the Earth on the tubing 3 and/or casings 4-5, and the geometry of the tubing 3 and casings 4-5.

The pressures P1 and P2 act upon the moveable member 105 in substantially opposite directions such that a net force is produced upon the moveable member 105 that is substantially smaller than the resultant force produced upon the moveable member 105 by either of pressures P1 or P2 when considered in isolation. The moveable member 105 moves in response to a combination of this net force and the force applied to it by the biasing member 110. As such, by providing a pressure in the second fluid region P2, the biasing member 110 is only required to act against the net force resulting from the difference in pressure between P1 and P2 such that the force required to be provided by the biasing member is advantageously reduced relative to an arrangement in which no pressure P2 is provided.

For example, as described above, the pressure in the second fluid region P2 may be 2.8 kpsi (19.3 MPa) and the threshold pressure required to open the shuttle valve 100 may be 3 kpsi (20.7 MPa). As such, the biasing member 110 is only required to act against the force arising from a differential pressure of 200 psi (1.38 MPa), rather the whole of the pressure of the fluid in the first fluid region (3 kpsi [20.7 MPa]).

It will be appreciated that properties of the biasing member that affect the force applied by the biasing member on the moveable member can be varied based upon the difference between the pressure P1 of the first fluid region and the pressure P2 of the second fluid region. It will be appreciated that a force applied by a biasing member is generally a factor of the size of the biasing member and a type of the biasing member. Given that the force applied on the moveable member by the biasing member is reduced, the size and type of the biasing member may be varied.

It will be understood that the term “size” in relation to the biasing member 110 may refer to an axial length of the biasing member 110 or may refer to a diameter of the biasing member 110. In general terms, the size of the biasing member is determined taking into account the space within the casings to accommodate the biasing member and the spring, and it will be appreciated that the use of a pressure P2 allows the size of the spring and biasing member to be reduced so as to more easily be accommodated within the casings. For example the axial length of the biasing member may be approximately 2-3 inches (50.8 - 76.2 mm). The biasing member may be a helical spring, and the size of the biasing member 110 may further be defined by a diameter of the biasing member 110, being the diameter of the helix scored by the helical spring. For example, the diameter of the biasing member 110 may be 0.5 inches (12.7 mm).

It will be understood that the term “type” in relation to the biasing member 110 may refer to the specific construction of the biasing member 110, for example whether the biasing member 110 is configured to urge against the moveable member 105 when the biasing member 110 is compressed, or whether the biasing member 110 is configured to urge against the moveable member 105 when the biasing member 110 is in tension. It will further be understood that the type of biasing member 110 may be defined by whether the biasing member 110 is a spring, a tension spring, a leaf spring, or any other resiliently deformable member. Furthermore, the type of biasing member 110 may be defined by the material of the biasing member 110 and the spring constant k of the biasing member 110. For example, the biasing member may be composed of a high yield strength material which is resistant to corrosion such as a nickel-based steel alloy such as nickel alloy 718. It will be understood that properties of the biasing member 110 may be selected such that when the biasing member 110 is deflected, the spring constant k of the biasing member 110 is sufficient to counteract the force produced upon the moveable member 105 by the pressure differential between the pressure P1 of the first fluid region and the pressure P2 of the second fluid region.

It will be understood that the properties of the biasing member may additionally be varied based upon the size of the cross-sectional area of the moveable member 105. The force that the biasing member produces to counteract the net force produced on the moveable member 105 by the first and second fluid regions is equal to the product of the pressure differential between P1 and P2, and the cross-sectional area of moveable member 105. Therefore, for a given pressure differential, reducing the size of the cross-sectional area of the moveable member 105 will result in a lower resultant force produced on the moveable member 105 by the pressure differential, and therefore a smaller biasing member 100 may be chosen.

Figures 6, 7 and 8 show a second embodiment of the pressure control system 10 of the present invention. It will be appreciated that the features of the invention which are common to both the first embodiment and the second embodiment retain the same reference signs.

The second embodiment includes a fluid flow passage 108 which is fluidly connected to the cavity 106 at a first end of the fluid flow passage 108 via a first opening 109, and is fluidly connected to the cavity 106 at a second end of the fluid flow passage 108 via a second opening 111. The first opening 109 is positioned such that when the moveable member 105 is in the closed configuration, such as that shown in Figure 6, the first opening 109 is blocked by the presence of the movable member 105 and fluid flow into the fluid flow passage 108 from the first fluid region is substantially prevented. When the moveable member 105 is in the open configuration, such as that shown in Figure 7, the moveable member 105 no longer covers the first opening 109 and fluid flow from the first fluid region into the fluid flow passage 108 is permitted.

The second opening 111 is positioned such that when the moveable member 105 is in the open configuration, fluid from the first fluid region may pass into the second fluid region via the fluid flow passage 108. That is to say, when the moveable member 105 is in the open configuration, at least a portion of the first opening 109 is exposed to the first fluid region and at least a portion of the second opening 111 is exposed to the second fluid region such that the fluid flow passage 108 is in fluid flow communication with both the first fluid region and the second fluid region. For example, an uppermost portion of the second opening 111 may be axially spaced from a lowermost portion of the first opening 109 along the cavity 106 by a distance D. In order to permit fluid flow from the first flow region to the second flow region through the fluid flow passage, the distance D is greater than an axial length L of the moveable member 105 which is the maximum length of the moveable member 105 parallel to the longitudinal axis of the cavity 106. It will be appreciated that the axial length L of the moveable member 105 and distance D between the first and second openings 109, 111 may be sized such that when the moveable member 105 is in the open configuration substantially the whole of the first opening 109 is exposed to the first fluid region and substantially the whole of the second opening 111 is exposed to the second fluid region.

When the pressure P1 in the first fluid region rises above a threshold pressure, the moveable member 105 is displaced by the pressure P1 of the fluid in the first fluid region acting on the moveable member 105. The pressure P1 acts to move the moveable member 105 into the open configuration. Fluid from the first fluid region then passes into the fluid flow passage 108 via the first opening 109, resulting in a decrease in the pressure P1 of the fluid in the first fluid region. The fluid then passes from the fluid flow passage 108 and into the second fluid region via the second opening 109. That is to say, the fluid from the fluid flow passage re-enters the cavity 106 on substantially the opposite side of the moveable member 105 as the first fluid region. Fluid within the second fluid region may pass from the cavity 106 and into the outlet conduit 102, where the pressure P2 of the fluid in the second fluid region is regulated by the isolation valve 104. As high pressure fluid from the first fluid region passes into the lower pressure second fluid region, the pressure P1 of the fluid in the first fluid region decreases. As the pressure P1 of the fluid in the first fluid region decreases, the net force produced upon the moveable member 105 by the first and second fluid regions also decreases. Because the moveable member is held in equilibrium between the force applied by the moveable member 105 and the net force produced by the first and second fluid regions, the force applied to the moveable member 105 by the biasing member 110 also decreases as the net force applied by the first and second fluid regions decreases, and therefore the biasing member 110 extends in response to the reduced net force. The biasing member 110 therefore urges the moveable member 105 towards the closed configuration and the first opening 109 is blocked by the moveable member 105 such that further fluid flow from the first fluid region into the fluid flow passage 108 is prevented.

It will be appreciated that the pressure of the fluid in the second fluid region P2, the threshold pressure, and the mechanical and geometrical properties of the biasing member 110 may be selected so as to minimise the amount of time in which the moveable member 105 is in the open configuration. In particular, because the biasing member 110 acts to urge the moveable member 105 towards the closed configuration, once a sufficient amount of fluid has been vented from the first fluid region, the moveable member 105 will return to the closed configuration. As such, under normal operating conditions, the moveable member 105 may only uncover a small portion of the second opening 109 of the fluid flow passage before returning to a closed configuration in which the second opening 109 is fully covered by the moveable member 105. However, the closed configuration of the moveable member 105 may be such that the moveable member 105 remains in a position displaced only by a small distance to that of the position of the moveable member 105 when the second opening 109 is partially uncovered. Therefore, the moveable member 105 may rapidly fluctuate between the open configuration and the closed configuration, without remaining in the open configuration for a prolonged period of time.

Figure 8 shows a deadlock configuration of the moveable member 105. The deadlock configuration is a third configuration of the moveable member 105 of the embodiment of Figures 6 to 8, in which fluid flow from the first fluid region to the second fluid region is substantially prevented. As shown in Figure 8, the moveable member 105 is urged into the deadlock configuration when the fluid in the second fluid region is unpressurised, which may occur, for example, during maintenance of the well 1 when the treehead 7 (containing the isolation valve 104) is removed and the outlet conduit 102 is exposed to the external environment. Because the fluid in the second fluid region is unpressurised, the fluid in the second fluid region no longer exerts a force upon the moveable member 105 in the direction of the closed configuration. As such, the force produced upon the moveable member 105 by the fluid in the first fluid region is significantly greater than the force produced upon the moveable member 105 by the biasing member 110. The moveable member 105 is therefore urged to an end of the cavity 106 remote from the inlet conduit 101, referred to above as the deadlock configuration.

The outlet conduit 102 and the second opening 111 of the fluid flow passage 108 are positioned such that when the moveable member 105 is in the deadlock configuration both the outlet conduit 102 and the second opening 111 of the fluid flow passage 108 are blocked by the moveable member 105. As such, fluid flow into or out of the outlet conduit 102 and the fluid flow passage 108 is substantially prevented by the moveable member 105.

It will be appreciated that when the fluid in the second fluid region is unpressurised it will have a gauge pressure (i.e. the pressure of the fluid relative to the pressure of the environment surrounding the well 1) of zero. Although the gauge pressure of the fluid in the second fluid region is zero, it will be appreciated that the absolute pressure of the fluid in the second fluid region may be non-zero. For example, where the well 1 is positioned on land, the absolute pressure of the fluid in the second fluid region may be atmospheric pressure. Alternatively, where the well 1 is positioned underwater, the absolute pressure of the fluid in the second fluid region may be dependent upon the depth of the well 1 below sea level.

Because the fluid in the second fluid region is unpressurised, no resultant force is produced upon the moveable member 105 by the fluid in the second fluid region. As such, the only force acting on the moveable member 105 to urge the moveable member 105 towards the closed configuration is the force applied by the biasing member 110. It will be appreciated that the magnitude of the force applied by the biasing member 110 is small in comparison to the resultant force produced upon the moveable member 105 by the pressure P1 of the fluid in the first fluid region. The moveable member 105 is therefore urged against the biasing member 110 by the pressure P1 of the fluid in the first fluid region such that the moveable member 105 covers the opening 111 of the fluid flow passage 108 and the outlet conduit 102. As such, fluid in the first fluid region is substantially prevented from escaping the cavity 106 when the second fluid region becomes unpressurised (i.e. when the treehead 7 is removed).

Figure 9 shows a third embodiment of a pressure control system according to the present invention. The pressure control system comprises a first shuttle valve assembly 100 and a second shuttle valve assembly 200. Both the first shuttle valve assembly 100 and the second shuttle valve assembly 200 are substantially identical to the shuttle valve assembly 100 depicted above with reference to the second embodiment of the invention (Figures 6-8). Both shuttle valve assemblies 100, 200 are joined by a common inlet conduit 101 fluidly joined to the annulus B, so as to allow fluid flow communication between each of the shuttle valve assemblies 100, 200 and the annulus B. The shuttle valve assemblies 100, 200 are further joined by a common outlet conduit 102 such that both shuttle valve assemblies 100, 200 are in fluid flow communication with a pressure sensor 103 and an isolation valve 104. As described above, the pressure sensor 103 and isolation valve 104 are operable to control the pressure P2 of the fluid within the outlet conduit 102.

The first shuttle valve assembly 100 comprises a first biasing member 110 configured to act upon a first moveable member 105; and the second shuttle valve assembly 200 comprises a second biasing member 210 configured to act upon a second moveable member 205. The biasing members 110, 210 are selected so that each biasing member produces a different amount of force upon their respective moveable members 105, 205 in response to pressure changes in the annulus B. For example, the spring constant of the second biasing member 210 may be less than the spring constant of the first biasing member 105. As such, when the pressure in the annulus B reaches a first threshold pressure, the moveable member 205 of the second shuttle valve 200 may move to the open configuration whilst the first shuttle valve 100 may remain in the closed configuration, as shown in Figure 9. As such, fluid from the annulus B may be vented to the outlet conduit 102 via only one of the shuttle valve assemblies 100, 200. However, where the pressure in the annulus B increases to a second threshold pressure, the moveable member 105 of the first shuttle valve 100 may also move to the open configuration to allow fluid from both shuttle valve assemblies 100, 200 to vent into the outlet conduit 102.

It will be appreciated that although the embodiment of the invention above is described in the context of two shuttle valve assemblies 100, 200 connected in parallel by their inlet and outlets, the pressure control system may comprise any number of additional shuttle valve assemblies connected in parallel.

It will be appreciated that although the shuttle valve assemblies 100, 200 are described as being substantially identical to the shuttle valve 100 of the second embodiment of the invention, the shuttle valve assemblies 100, 200 may be substantially identical to the shuttle valve 100 of the first embodiment of the invention (i.e. one in which the fluid flow passage 108 is connected directly to the outlet conduit 102).

Claims

CLAIMS:

1. A pressure control system for an oil or gas well, comprising: a moveable member moveable between an open configuration in which fluid is permitted to flow from a first region of the well to a second region of the well and a closed configuration in which fluid flow from the first region to the second region is prevented; a biasing member configured to urge the moveable member towards the closed configuration; and a pressure controller, wherein the pressure controller is arranged to control a pressure that acts on the moveable member to urge the moveable member towards the closed configuration.

2. A pressure control system according to claim 1, wherein a property of the biasing member is selected based upon the pressure that acts on the moveable member to urge the moveable member towards the closed configuration.

3. A pressure control system according to claim 1 or 2, wherein the moveable member is moveable within a cavity fluidly connected to the first region and the second region.

4. A pressure control system according to any preceding claim, wherein the moveable member is configured to selectively permit fluid flow from the first region to the second region via a flow passage fluidly connecting the first region to the second region.

5. A pressure control system according to claim 4, wherein the moveable member is configured to substantially cover a first opening of the flow passage when the moveable member is in the closed configuration such that fluid flow communication between the first opening and the first region is substantially prevented.

6. A pressure control system according to claim 5, wherein the first opening is in fluid flow communication with the first region when the moveable member is in the open configuration.

7. A pressure control system according to any of claims 5 or 6 when dependent upon claim 3, wherein the first opening of the fluid flow passage is an opening of the cavity.

8. A pressure control system according to any preceding claim, wherein the moveable member is arranged such that in use a pressure acts upon the moveable member to urge the moveable member towards the open configuration.

9. A pressure control system according to claim 8, wherein the pressure controller is arranged to control the pressure that acts on the moveable member to urge the moveable member towards the closed configuration based upon the pressure that acts upon the moveable member to urge the moveable member towards the open configuration.

10. A pressure control system according to any preceding claim, wherein the pressure that acts upon the moveable member to urge the moveable member towards the closed configuration is associated with the second region.

11. A pressure control system according to any preceding claim, wherein the moveable member is moveable to a further closed configuration in which fluid flow from the first region to the second region is prevented when the pressure that acts on the moveable member to urge the moveable member towards the closed configuration is below a predetermined threshold.

12. A pressure control system according to claim 11, wherein the moveable member is configured to substantially cover a second opening of the flow passage when the moveable member is in the further closed configuration.

13. A pressure control system according to claim 12 when dependent on claim 3, wherein the second opening of the flow passage is an opening of the cavity.

14. A pressure control system according to any of claims 12 or 13 when dependent upon any of claims 4 to 6, wherein a distance between the first opening and the second opening is configured based upon a size of the moveable member.

15. A pressure control system according to any preceding claim, wherein the first region is in fluid flow communication with an annulus of the oil or gas well.

16. A pressure control system according to any preceding claim, further comprising a pressure sensor arranged to determine a pressure of the second region.

17. A pressure control system according to any preceding claim, further comprising an isolation valve configured to selectively permit fluid flow from the second region to an environment external to the well.

18. A pressure control system according to claim 17, wherein the pressure controller communicates with the isolation valve to selectively actuate the isolation valve based upon a pressure sensed by the pressure sensor.

19. An assembly for controlling pressure comprising: a first pressure control system according to any preceding claim; and a second pressure control system according to any preceding claim; wherein a first biasing member of the first pressure control system is configured to permit the first moveable member to move to the open configuration at a first threshold pressure of the first region and a second biasing member of the second pressure control system is configured to permit the second moveable member to move to the open configuration at a second threshold pressure of the first region.

20. An oil or gas well comprising: a wellbore; a first tubular member contained within the wellbore; a second tubular member circumferentially surrounding at least a portion of the first tubular member to define a spacing between the first tubular member and the second tubular member and within which a fluid is contained; and a pressure control system according to any of claims 1-19 arranged to fluidly communicate with the fluid contained within the spacing.