The present invention relates to a downhole valve assembly, an actuation device for a downhole valve assembly, and to a method of controlling fluid flow downhole. In particular, but not exclusively, the present invention relates to a downhole valve assembly having a generally tubular body defining a fluid flow path therethrough and having a valve mounted in the body for controlling fluid flow through the fluid flow path; to an actuation device for such a downhole valve assembly; and to a corresponding method of controlling fluid flow downhole.
As is well known in the oil and gas exploration and production industry, a wellbore or borehole is drilled from surface in order to gain access to subterranean hydrocarbon deposits (oil and gas). The wellbore is typically drilled to a first depth and then lined with a steel casing which is cemented in place, both to support the drilled rock formations, and to prevent unwanted fluid ingress/egress. The wellbore is then extended to a further depth and a smaller diameter casing is located in the extended section, passing through the wellbore to surface, and which is also cemented in place. This process is repeated as necessary until the wellbore has been extended to a desired depth. If required, a liner may be located in the final drilled section, the liner tied in to the deepest section of casing in the wellbore. The well is then completed, which involves carrying out various downhole procedures so that well fluids can be recovered to surface through production tubing located in the cased wellbore.
During completion of the wellbore, it is necessary to test the integrity of the casing/liner located in the wellbore, to ensure a pressure-tight seal has been obtained. This is achieved by running-in a tubing string carrying a downhole valve assembly, and locating and sealing the valve assembly in the casing/liner. The valve assembly typically includes a ball valve which is initially in an open position that permits fluid flow and tool passage along a body of the valve assembly, and thus enables further completion procedures to be carried out. Once the further procedures have been carried out, the valve is actuated to move the ball valve to a closed position.
In the closed position, the ball valve prevents further fluid flow/tool passage along the body flow path, and thus effectively isolates a portion of the wellbore below the valve from the portion above. A pressure-test can then be carried out, to verify the integrity of the casing/liner above the valve. Following completion of the pressure test, the valve can be actuated to move the ball valve back to the open position, enabling further downhole operations to be carried out.
The ball valves of existing downhole valve assemblies are typically mounted in ball cages which are translated axially relative to the body of the valve in order to move the ball valve between its open and closed positions. The valve assemblies are actuated to move the ball valves between their open and closed positions using applied fluid pressure, which is communicated to an actuation mechanism of the assembly. The actuation mechanisms are usually provided adjacent to and/or immediately uphole of the ball valve itself.
Providing valve assemblies in which the ball valve and ball cage are translated axially between open and closed positions can present problems in use of the valve assemblies. In particular, solids debris particles present in the wellbore have a tendency to settle out over time. Accordingly, when the valve assembly has been actuated to move the ball valve to a closed position, the solids debris tends to settle on the ball valve itself, and can build up into a deposit of significant depth. As a result, the ball valve can become jammed and incapable of the axial translation necessary to move the ball valve between its open and closed positions. Furthermore, the solids deposit can also cause the actuation mechanism to become blocked or jammed.
Consequently, the ball valve can become jammed closed, requiring remedial action to be taken to reopen the wellbore, which may include milling or drilling out the jammed ball valve. Such procedures are costly to carry out; result in serious damage to the valve assembly; produce large volumes of swarf which requires to be circulated out of the wellbore before well operations can resume; and results in a costly suspension of well operations.
It is therefore amongst the objects of at least one embodiment of the present invention to obviate or mitigate at least one of the foregoing disadvantages.
According to a first aspect of the present invention, there is provided a downhole valve assembly comprising:
a generally tubular body defining a fluid flow path therethrough;
a valve mounted within the body, the valve movable between an open position and a closed position for thereby controlling the flow of fluid along the fluid flow path;
a valve actuation mechanism mounted within the body, the actuation mechanism located in a position which is, in use, downhole of the valve; and
a fluid communication arrangement for communicating fluid pressure to the valve actuation mechanism to facilitate operation of the valve actuation mechanism and thereby operation of the valve, the fluid communication arrangement comprising a fluid inlet port which is, in use, located uphole of the valve.
Providing a downhole valve assembly with a valve and a valve actuation mechanism located downhole of the valve offers significant advantages over prior valve assemblies. This is because, in the event that solids present in fluid in a wellbore settle on the valve when the valve is closed, these solids cannot cause the actuation mechanism to become jammed or stuck, and therefore cannot affect actuation of the valve. Furthermore, providing such a valve assembly in which the fluid inlet port is provided uphole of the valve still permits control of and actuation of the valve in response to fluid pressure or fluid communication from uphole of the valve.
The actuation mechanism may be adapted to exert a force on the valve to move the valve between the open and closed positions in response to an applied fluid pressure. In a preferred embodiment, the actuation mechanism is arranged to exert a force on the valve to move the valve from the closed position to the open position.
The actuation mechanism may comprise a force transmission arrangement for transmitting a force to the valve to move the valve between the open and closed positions, preferably for moving the valve from the closed position to an open position. The force transmission arrangement may comprise an actuating member and a coupling member, the actuating member connected to the coupling member and the coupling member connected to the valve, to facilitate transmission of a force from the actuating member to the valve.
The actuating member may be connected to the coupling member via a connector which facilitates limited axial movement of the coupling member relative to the actuating member. This may facilitate movement of the valve between the open and closed positions, preferably from the closed position to the open position, by application of an external force. The connector may permit a limited movement of the coupling member relative to the actuating member in a direction towards the valve which may, in use, be an uphole direction.
The actuating member may be selectively restrained against axial movement relative to the body, and may be biased for movement in a direction away from the valve which may, in use, be a downhole direction.
The actuating member may be selectively restrained by a locking arrangement and may, when the locking arrangement is actuated, be released for movement under a biasing force in the direction away from the valve. Such movement may carry the coupling the member and may thereby move the valve from the closed position to the open position.
The locking arrangement may comprise an at least one lock member adapted to restrain the actuating member against movement relative to the body, and at least one release member adapted to exert a release force on an or each lock member, to cause the or each lock member to release the actuating member for movement relative to the body. The locking arrangement may further comprise an at least one locking dog, key, button or the like, the or each dog movable from a release position out of engagement with the actuating member to a locking position in engagement with the actuating member, for restraining the actuating member against movement relative to the body. The or each locking dog may be adapted to co-operate with the lock member and may be supported in engagement with the actuating member by the lock member when in the locking position. The release member may be adapted to be actuated to move the lock member and desupport the locking dog in response to an applied fluid pressure.
The actuation mechanism may include a pressure sensor for measuring pressure in a wellbore in which the assembly is located, and means for setting a reference pressure value using a measurement obtained by the pressure sensor. In this fashion, when pressure applied to the assembly meets a predetermined condition, such as falling within a pressure window for a certain time period, the actuation mechanism may be actuated to move the valve. This method of operating the actuating mechanism is disclosed in detail in the Applicant's International Patent Publication Number WO 2007/049046, the disclosure of which is incorporated herein by way of reference.
The actuation mechanism may take the form of a primary valve actuation mechanism, and the assembly may further comprise a secondary valve actuation mechanism. The secondary actuation mechanism may comprise a fluid actuated override member, which may take the form of an override piston. The override member may be located, in use, downhole of the valve and adapted to exert a force on the valve for moving the valve between the open and closed positions, preferably from the closed position to the open position. Providing the override member downhole of the valve prevents blockage and jamming of the override piston through build-up of solids, and provides an emergency override for actuating the valve, preferably for opening the valve.
The override member may be adapted to exert a force on the coupling member of the primary actuation mechanism, for moving the valve.
The secondary actuation mechanism may further comprise an operating member which may take the form of a sliding sleeve provided, in use, uphole of the valve. The operating member may be fluidly coupled to the override member and may serve for controlling movement of the override member. The operating member may be mounted for movement within the body, movement of the operating member pumping fluid to the override member to thereby move the valve. The operating member may be adapted to be moved to pump fluid to the override member by a downhole tool run into the assembly and engaged with the operating member, which downhole tool may be a stinger or the like.
Preferably, the valve is a ball valve and is mounted for rotation relative to the body, to facilitate movement of the valve between its open and closed positions. The ball valve may be secured against axial movement relative to the body, which may be achieved by journalling or otherwise rotatably mounting the ball valve to the body. In a particular embodiment, the ball valve may comprise trunnions or other mounting members for mounting the ball valve to the body, the trunnions extending through a ball cage, the ball cage adapted to co-operate with the ball valve for moving the ball valve between the open and closed positions. Where the actuation mechanism comprises a coupling member, the coupling member may be coupled to the ball cage.
The ball valve may comprise a surface defining at least one recess therein, the recess adapted to define a guide for guiding a cutting tool into contact with the ball valve, a wall thickness of the ball valve in a region adjacent a base or root of the recess being smaller than a wall thickness of the ball valve laterally spaced from the base. Providing such a recess facilitates cutting of the ball valve in the event that the valve becomes stuck or jammed in the closed position, and thus facilitates reopening of a wellbore in which the assembly is located in the event that the ball valve becomes jammed closed. It will be understood that the cutting tool may be a drill, mill or other abrading/abrasive tool.
The surface of the ball valve carrying the recess may be adapted to face uphole, in use, when the ball valve is in the closed position. The recess may be circular, and at least one side wall of the recess may be inclined relative to an axis of the ball valve which is parallel to a main axis of the body when the ball valve is in the closed position. This may facilitate guiding of a cutting tool such as an annular milling tool, having cutting elements on a leading edge thereof, into engagement with the ball valve.
The ball valve may comprise at least one further recess, and the at least one further recess may be disposed on an axis of the ball valve which is parallel to the main axis of the body when the ball valve is in the closed position. The further recess may facilitate guiding of a drill bit into engagement with the ball valve.
The or each recess of the ball valve may be at least partly filled with a material having a lower hardness in comparison to a material of a main part/remainder of the ball valve. Filling the or each recess with such a material prevents blockage of the recess through solids settlement, but is easily milled or cut out should it prove necessary to drill out the ball valve. The material may be a softer metal, an elastomeric material or a plastics material.
According to a second aspect of the present invention, there is provided an actuation device for a downhole valve assembly, the actuation device comprising:
a valve actuation mechanism adapted to be mounted in a generally tubular body of a downhole valve assembly in a position which is, in use, downhole of a valve mounted within the body of the downhole valve assembly; and
a fluid communication arrangement for communicating fluid pressure to the valve actuation mechanism to facilitate operation of the valve actuation mechanism and thereby operation of the valve, the fluid communication arrangement comprising a fluid inlet port which is adapted, in use, to be located uphole of the valve.
Further features of the actuation device are defined above in relation to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a method of controlling fluid flow downhole, the method comprising the steps of:
locating a downhole valve assembly in a wellbore;
directing fluid in the wellbore into a fluid flow path extending through a generally tubular body of the assembly;
arranging a valve of the assembly mounted within the body in one of an open position and a closed position; and
applying fluid pressure to a valve actuation mechanism of the assembly located downhole of the valve using a fluid communication arrangement of the assembly, the fluid pressure applied through a fluid inlet port of the arrangement located uphole of the valve, to operate the actuation mechanism and thereby move the valve to the other one of the open position and the closed position so as to control the flow of fluid along the fluid flow path.
The method may comprise the step of running the downhole valve assembly into the wellbore with the valve of the assembly in an open position, and then locating the assembly downhole with the valve in the open position. The valve may then be moved to a closed position, which may be achieved using a downhole tool such as a stinger, the downhole tool adapted to exert a force on the valve to move the valve to the closed position. Following closing of the valve, further downhole procedures may be carried out. Such procedures may comprise pressure testing the integrity of downhole tubing such as a casing and/or liner in which the assembly is located.
On completion of further downhole procedures, the valve may be returned to an open position. This may be achieved by the step of applying fluid pressure to the valve actuation mechanism, which may exert a force on the valve to move the valve back to the open position. The step of applying fluid pressure to the actuation mechanism may comprise pressurising fluid in the wellbore above the valve to a pressure which is within a determined pressure window, and/or applying pressure for a determined time period, in response to which the actuation mechanism may be activated to thereby move the valve to the open position.
According to a fourth aspect of the present invention, there is provided a ball valve comprising:
a valve element having a bore extending therethrough, the valve element adapted to be mounted within a generally hollow body and being rotatable between an open position in which the valve element permits fluid flow along the body through the bore of the valve element and a closed position in which the valve element prevents fluid flow along the body; wherein the valve element comprises a surface defining at least one recess adapted to define a guide for guiding a cutting tool into contact with the valve element, to facilitate cutting of the valve element in the event that the valve element becomes stuck in the closed position.
Preferably, the ball valve is a ball valve for a downhole valve assembly. However, the ball valve may have a utility with other types of valve assembly.
Further features of the ball valve are defined above in relation to the first aspect of the present invention.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Turning firstly to
The valve assembly 10 is shown in more detail in the longitudinal half-sectional views of
In general terms, the valve assembly 10 is operated as follows. The valve assembly 10 is run-in to the wellbore 12 in the run-in configuration shown in
Following completion of the wellbore 12, the tubing string 18 may be disconnected from the hanger/packer tool assembly 20 and returned to surface, and the valve assembly 10 actuated to close the ball valve 22. A pressure-test operation is then carried out to test the integrity of the casing 14, to ensure no leak paths exist for the ingress or egress of fluid into or out of the casing 14. The valve assembly 10 therefore effectively closes and seals the wellbore 12 at a level below the ball valve 22, and the pressure of fluid in the casing 14 above the ball valve may then be raised and monitored for a desired time period. Any leak paths present will cause a reduction in the pressure of fluid in the casing 14 which can be detected at surface, providing an indication that remedial action is required before production of wellbore fluids can commence.
On completion of a successful pressure-test operation, the valve assembly 10 may be actuated to reopen the ball valve 22. This is achieved by communicating a fluid pressure signal to the actuation mechanism 28 using the fluid communication arrangement 30. Specifically, fluid pressure is communicated to the actuation mechanism 28 through the fluid inlet port 32 and a primary control line 34, which is shown schematically in
By providing the actuation mechanism 28 downhole of the ball valve 22, any solids present in fluid in the casing 14, which would tend to settle on the ball valve 22 following closure, are prevented from falling further downhole beyond the ball valve 22. Accordingly, these solids cannot hamper actuation of the mechanism 28. Furthermore, by providing the fluid communication arrangement 30 with an inlet port 32 uphole of the ball valve 22, the pressure of fluid in the casing 14 above the ball valve 22 can be communicated to the actuation mechanism 28 to selectively actuate the ball valve 22. The fluid inlet port 32 is spaced a sufficient distance from the ball valve 22 such that, in the event of solids build-up on the closed ball valve 22, the solids will not block the port 32 and restrict operation of the valve assembly 10.
The valve assembly 10 will now be described in more detail.
Viewing generally from top to bottom in
The actuation mechanism 28 in fact forms a primary actuation mechanism, and the assembly 10 includes a secondary actuation mechanism 48. Secondary actuation mechanism 48 includes an operating member in the form of a sliding sleeve 50 which is mounted for sliding movement within the upper sub 36 and an intermediate sub 52 which is coupled to the upper sub 36. The secondary actuation mechanism 48 also includes a fluid actuated override member in the form of an annular override piston 54, which is shown in
The intermediate sub 52 is connected via a pup joint 72 to a further intermediate sub 74, to which a body section 76 is coupled. A further body section 78 is in-turn coupled to the body section 76 and a valve mounting section 80 is coupled to the body section 78. The ball valve 22 includes trunnions, one of which is shown and given the reference numeral 82, by which the ball valve 22 is rotatably mounted to the valve mounting section 80, the trunnions 82 located in apertures 84 in the valve mounting section. As the valve mounting section 80 is coupled to the second body section 78, the ball valve 22 is effectively held against axial movement relative to the body 24.
The ball valve 22 is located within a ball cage 86 which is itself mounted for sliding movement within the valve mounting section 80 and which, as will be described below, serves for moving the ball valve 22 between the open and closed positions. A ball sleeve 88 is mounted for sliding movement within and relative to the intermediate sub 74 and body section 76, and defines an annular spring chamber 90 between an outer surface of the ball sleeve 88 and an inner surface of the body section 76, in which a spring 92 is located. The spring 92 serves for biasing the ball sleeve 88 in a direction towards the ball valve 22. The ball sleeve 88 is connected via a rod 94 and coupling sleeve 96 to an upper cage sleeve 98, which is secured to the ball cage 86. Lips 100, 102 on the coupling sleeve 96 and upper cage sleeve 98 provide for a degree of axial movement of the ball sleeve 88 relative to the ball cage 86, and the lips 100, 102 are shown in
Below the ball valve 22, the ball cage 86 is connected to a coupling member 104 which forms part of the primary actuation mechanism 28. The coupling member 104 includes an upper sleeve 106 which is secured to a main tubular section 108, the upper sleeve 106 including a lip 110 which cooperates with and engages a lip 112 on a lower end of the ball cage 86. Engagement between the lips 110, 112 permits a force to be exerted on the ball cage 86 in a downhole direction, to move the ball valve 82 from a closed position to the open position, as will be described below. An annular chamber 114 is defined between an outer surface of the main tubular section 108 and inner surfaces of the valve mounting section 80 and an intermediate sub 116 which is coupled to the valve mounting section 80. The override piston 54 is located in the chamber 114 and carries an O-ring 118 on a shoulder 210 for sealing the override piston to the intermediate sub 116. Additionally, O-rings 120 and 122 are provided in the valve mounting section 80 and the intermediate sub 116. Passages 124, 126 extend through walls of the valve mounting section 80 and the intermediate sub 116, respectively, and are coupled to the control lines 68 and 70. Accordingly, the passage 64 opening on to chamber 62 is in fluid communication with the annular chamber 114 through the passage 124. In a similar fashion, the passage 66 opening on to annular chamber 62 is in fluid communication with the annular chamber 114 via the passage 126. Accordingly, and as will be described in more detail below, movement of the sliding sleeve 50 can effect a corresponding movement of the override piston 54. In the configuration of the valve assembly 10 shown in
The coupling member 104 also includes a lower tubular section 128 which is threaded to a short sleeve 130, whilst the main tubular section 108 carries a similar short sleeve 132. As shown particularly in
The outer tubular section 142 of the body 24 is coupled to a lock sub 148, which forms part of a locking arrangement 150 of the assembly 10. The locking arrangement 150 includes a lock member in the form of a lock sleeve 152, which serves for locking the lower sleeve 146 (and thus the ball cage 86) against movement relative to the lock sub 148, and thus for locking the ball valve 22 against rotation relative to the body 24. The locking arrangement 150 also includes a number of locking dogs, one of which is shown and given the reference numeral 154, the locking dogs located in apertures 156 extending through a wall of the lock sub 148. In the position shown in
A body sleeve 162 couples the lock sub 148 to an intermediate sub 164 which includes a number of axial passages extending therethrough, one of which is shown and given the reference numeral 166. Release members of the locking arrangement 150, in the form of release rods 168, are mounted in the passages 166 for sliding movement relative to the intermediate sub 164. The release rods 168 serve for transmitting a force to the lock sleeve 152, to selectively release the lower sleeve 146 of the coupling member 104 for movement relative to the body 24.
An outer sleeve 170 of the primary actuation mechanism 28 is coupled to the intermediate sub 164 and, together with an inner sleeve 172, defines a chamber 174 in which further components of the actuation mechanism 28 are located. Following the teachings of WO 2007/049046, the primary actuation mechanism 28 includes a pressure transducer 176, control circuitry 178 and power cells 180. These, together with a number of pyrotechnic charges, one of which is shown and given the reference numeral 182, are located within and sealed in the chamber 174. Finally, at a lower end of the valve assembly 10, the body 24 includes a lower sub 184 which carries a male (pin) connector 186 for coupling to downhole tubing 188 (
The method of operation of the valve assembly 10 will now be described in more detail.
The valve assembly 10 is run-in to the wellbore 12 with the ball valve 22 in the open position shown in
As the ball cage 86 moves upwardly, engagement between the lip 110 on the upper sleeve 106 of coupling member 104, and the lip 112 on the ball cage 86 carries the upper sleeve 106, main tubular section 108 and short sleeve 132 upwardly. Thus closes the distance between the short sleeves 130, 132 on the lower tubular section 128 and main tubular section 108. However, the lower tubular section 128 remains restrained against movement by virtue of its connection with the lower sleeve 146, which remains fixed relative to the body 24 by the locking dogs 154.
The collet 196 can then be snapped-out of engagement with the ball sleeve 88 and returned to surface, whereupon the valve assembly 10 moves to the configuration shown in
Following completion of the pressure test, when it is desired to reopen valve assembly 10, the primary actuation mechanism 28 is actuated, as will now be described with reference to
The pressure is maintained within the predetermined pressure window for a specified period of time. When this occurs, pressure readings transmitted to the control circuitry 178 by the transducer 176 cause the circuitry to generate an output signal which ignites the pyrotechnic charges 182. When the charges 182 are fired, the release rods 168 are urged rapidly upwardly, thereby exerting a force on the lock sleeve 152. This shears the pins 160, releasing the lock sleeve 152 and carrying the lock sleeve a short distance uphole. The locking dogs 150 are now located adjacent a recess 204 in an inner surface of the lock sleeve 152. The spring 144 then urges the lower sleeve 146 of the coupling member 104 downwardly, interengagement between the recess 158 and tapered surfaces on the locking dogs 154 urging the dogs radially outwardly.
As the lower sleeve 146 moves down, carrying the lower tubular section 128, the short sleeve 130 on the tubular section 128 is brought into abutment with the short sleeve 132 mounted on the main tubular section 108 of the coupling member 104. Thus, as the lower sleeve 146 continues to move down, the upper sleeve 106 of coupling member 104 is also carried down. Engagement between the lip 110 on upper sleeve 106 and the lip 112 on the ball cage 86 moves the ball cage down, this rotating the ball valve 22 back to the open position, as shown in
The valve assembly 10 is shown in
Downward movement of the override piston 54 brings the piston into abutment with the abutment sleeve 134, and continued downward movement thus transmits a force to the main tubular section 108. As described above, engagement of the lips 110, 112 of the upper sleeve 106 of coupling member 104 and ball cage 86 then moves the ball cage down, rotating the ball valve 22 to the open position. This downward movement of the sliding sleeve 50 continues until such time as shoulders 208 and 210 on the sliding sleeve 50 and override piston 54, respectively, butt-out. It will be understood that, by this mechanism, the ball valve 22, and thus the valve assembly 10, may be reopened even in the event of failure of the primary actuation mechanism 28.
Turning now to
Turning now to
The ball valve 22 includes recesses 220, each of which are shaped to received dogs (not shown) on the ball cage 86, which serve for rotating the ball valve 22 about the trunnions 82, in a fashion known in the art.
Additionally, the ball valve 22 includes a surface 222 which includes a circular recess 224. A wall thickness of the ball valve 22 in the region of a root or base 226 of the recess 224 is smaller than adjacent portions of the ball valve. Furthermore, the recess 224 includes an inclined surface 228 which serves for guiding a cutting tool in the form of a milling tool 223, shown in
The surface 222 additionally includes a further, cone-shaped recess 236 which is shaped for receiving a drill bit extension 238 of the milling tool 230, which serves primarily for centring the milling tool 230 relative to an axis 240 of the ball valve 222.
If desired, the circular recess 224 and the cone-shaped recess 236 may be filled with a material of a lower hardness than a remainder of the ball valve 22, such as a softer metal, an elastomeric or a plastics material. Such materials may be relatively easy to mill or cut away, but may prevent the recesses 224, 236 from becoming blocked with solids deposits.
The ball valve 22 is shaped to include the recesses 224 and 236 to facilitate milling/cutting of the ball valve 22 in the event that the ball valve should for any reason become stuck in the closed position.
Various modifications may be made to the foregoing without departing from the spirit and scope of the present invention.
For example, although a valve assembly has been described which has a particular utility in downhole environments, it will be understood that the assembly (and the associated actuation device) of the present invention has a utility in other environments, and thus with or in other types of tools or tubing, such as pipelines or flowlines.
Although the above-described embodiments of the invention incorporate a valve in the form of a ball valve, it will be understood that other types of valves may be utilised, including flapper valves.
Although the primary actuation mechanism is described above as moving the valve from a closed to an open position, it will be understood that the valve assembly may be configured such that the primary actuation mechanism is utilised to move the valve from an open to a closed position. In this event and with the valve in an open position, pressure applied to the actuation mechanism through the fluid communication arrangement may be also be transmitted to producing and/or other formations downhole of the ball valve. It will be understood that the secondary actuation mechanism may similarly be configured to move the valve from an open to a closed position.
It will be understood that references herein to components of the valve assembly of the present invention being uphole, relative to a defined reference point, are to be construed as meaning further along a wellbore in a direction towards the surface (and thus to a position which is shallower in the wellbore). Equally, references herein to components of the valve assembly being downhole, relative to a defined reference point, are to be construed as meaning further along a wellbore in a direction away from the surface (and thus to a position which is deeper in the wellbore).
Number | Date | Country | Kind |
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0714614.5 | Jul 2007 | GB | national |