Abstract: A pressure driven pumping system includes a piston disposed within a first bore of a housing to separate a process chamber from a working chamber. A rod member coupled to the separating member extends into a reduced pressure chamber. The piston has a first face exposed to the process chamber and a second face exposed to the working chamber. The second face has an effective area less than an effective area of the first face. The housing may be placed in seawater at a selected depth. The process chamber can be in fluid communication with a well to pass well fluid into the process chamber at well pressure to move the piston, to discharge seawater from the seawater chamber. The working fluid, typically seawater in a subsea application, is pumped into the working chamber to move the piston, which discharges well fluid from the process chamber.

Abstract: A pressure relief device is used to relieve pressure in a void within a wellhead housing. In one embodiment, the pressure relief device includes a plunger having a stepped plug, wherein the plug can be fully open to allow flow from the void, restricted to allow a predetermined flow to relieve pressure, or closed to prevent flow from the void. In another embodiment, the pressure relief device includes a vacuum puller that creates negative pressure in a vessel. As fluid in the void expands, it is able to enter the space formerly occupied by the plunger. In yet another embodiment, a rupture disc is used to prevent fluid from flowing from the void, through a passage, to the wellbore. If pressure in the void exceeds a predetermined value, the rupture disc yields and allows the trapped fluid to flow to the wellbore.

Abstract: A method of reducing a pressure within a first cavity of a subsea device is disclosed which includes transferring fluid within the first cavity to an accumulator, increasing a pressure of the fluid within the accumulator and, after increasing the pressure of the fluid within the accumulator, transferring at least some of the fluid in the accumulator into a second cavity, wherein the second cavity is at a higher pressure than said first cavity.

Abstract: A method of unloading a well using a modular adapter having a pump, a pump suction line, and a pump discharge line. The adapter is connected to a subsea wellhead assembly so that the pump suction line communicates with a main bore in the wellhead assembly and the pump discharge line communicates with a production line attached to the wellhead assembly. The production line is isolated from the main bore and the pump draws fluid from within the well and discharges it into the production line. After unloading the well, the adapter can be removed and moved to another location for well unloading.

Abstract: A subsea completion assembly for a subsea well including installed casing and a wellhead. The assembly includes a production casing forming a B annulus between the outside of the production casing and the installed casing. The assembly also includes an annulus access adapter installed in the wellhead, the adapter including a manipulatable valve controlling fluid communication with the fluid in the B annulus across the annulus access adapter. A property of the fluid in the B annulus can be monitored by fluid communicated across the annulus access adapter.

Abstract: A subsea wellhead assembly provides a positive indication of landing of a wellhead member and locking of a wellhead member to a wellhead. The subsea wellhead assembly includes at least one positive indicator assembly disposed within a wellhead member, and a communication line extending down a running string from a platform to a running tool disposed in a subsea wellhead. The at least one positive indicator assembly provides confirmation of setting of the wellhead member, and the communication line is in communication with the positive indicator assembly to communicate the confirmation of setting with the platform following setting of the wellhead member.

Abstract: Cap (100) comprising a stinger adapted to be inserted into a bore (203) of a subsea well element (200), said stinger comprising locking means (101) for locking to an profile (207) in said bore, which locking means comprises a plurality of locking dogs (101) which exhibit a large inclination face (101a) and a small inclination face (101b, 101c), and which are adapted to be actuated in a radial direction by an actuation sleeve (109). The small inclination face is divided by a slot, in which slot the large inclination face is arranged, wherein a cam (131) arranged on the actuation sleeve is adapted to extend into said slot; or, the small inclination face is divided by a cam arranged on the locking dog, on which the large inclination face (131a) is arranged, which cam is adapted to extend into a slot in the actuation sleeve.

Abstract: The present invention generally relates to methods and apparatus for subsea well intervention operations, including retrieval of a wellhead from a subsea well. In one aspect, a method of performing an operation in a subsea well is provided. The method comprising the step of positioning a tool proximate a subsea wellhead. The tool has at least one grip member and the tool is attached to a downhole assembly. The method also comprising the step of clamping the tool to the subsea wellhead by moving the at least one grip member into engagement with a profile on the subsea wellhead. The method further comprising the step of applying an upward force to the tool thereby enhancing the grip between the grip member and the profile on the subsea wellhead. Additionally, the method comprising the step of performing the operation in the subsea well by utilizing the downhole assembly. In another aspect, an apparatus for use in a subsea well is provided.

Abstract: Provided is a system, including a first module (35b) configured to process fluid from a well, wherein the first module (35b) has an extension conduit (5b), having a connection that is coupleable to a central mandrel of a manifold (5), a processing device arranged in a region surrounding the extension conduit (5b), a processing input (18a), and a processing output (19a). Further provided is a method of processing well fluids, including diverting fluids from a bore of a manifold (1) to a processing module (35b), wherein the processing module (35b) is coupled to a mandrel of the manifold (5), processing the fluids in the processing module (35b), and returning the fluids to a flowpath (19a) for recovery.

Abstract: An oil recovery system recovers oil released at the bed of a body of water. The system includes a fluid collector assembly positionable proximate to the bed of the body of water. The collector assembly has an open lower end to receive fluid and has an upper end coupled to a lowermost fluid transfer tube. Fluid transfer tubes are interconnected in a string between the lowermost fluid transfer tube and a vessel positioned to receive fluid transferred through the fluid transfer tube. A guide cable is anchored at the bed of the body of water to guide the fluid collector assembly and the fluid transfer tubes to the bed. A lift cable selectively lowers the fluid collector assembly and the fluid transfer tubes to the bed. Fluid entering the collector assembly rises to the water surface via the transfer tubes.

Abstract: A wicker repair tool lands on a casing hanger within a wellhead. The wicker repair tool engages cutters with the inner diameter of the wellhead and rotates to reform wickers in the wellhead. The wicker repair tool includes a tubular member having an upper end that couples to a tubing string. A tubular tool head is formed on a lower end of the tubular member. At least one cutter is coupled to the tool head and is radially moveable between an engaged and a disengaged position. The cutters are adapted to engage an inner diameter surface of a wellhead so that rotation of the tool head relative to the wellhead will reform the wickers.

Abstract: An apparatus for use with a subsea well includes a lubricator configured to attach to subsea wellhead equipment, an electrically-activated tool, and a coiled tubing attached to the electrically-activated tool. The electrically-activated tool is initially provided in the lubricator to allow for deployment of the electrically-activated tool on the coiled tubing into the subsea well. Multiple tools may be deployed independently from within the lubricator to latch into a concentric electrical connector within the well which may also act as a switch. A concentric electrical connector will permit the passage of a tool through the body of the connector retaining full bore access when the tool is withdrawn.

Abstract: A completion system and method for completing a subsea well with angular alignment-free assembly The system includes a series of circumferential channels formed in a well completion device at a boundary between a tubing hanger and the completion device. The circumferential channels provide complete circular fluid paths with respect to the tubing hanger and the completion device. A supply bore and a drain bore are in communication with each circumferential channel and oriented to supply a fluid to and remove fluid from, respectively, the circumferential channel. A circumferential electrical connector couples the tubing hanger and the completion device. The circumferential channels and bores provide fluid services between the completion device and the tubing hanger and the electrical connector provides electrical services to the tubing hanger. The completion system allows the fluid and electrical services to be provided without requiring any angular alignment between the tubing hanger and the completion device.

Abstract: Methods and apparatus for diverting fluids either into or from a well are described. Some embodiments include a diverter conduit that is located in a bore of a tree. The invention relates especially but not exclusively to a diverter assembly connected to a wing branch of a tree. Some embodiments allow diversion of fluids out of a tree to a subsea processing apparatus followed by the return of at least some of these fluids to the tree for recovery. Alternative embodiments provide only one flowpath and do not include the return of any fluids to the tree. Some embodiments can be retrofitted to existing trees, which can allow the performance of a new function without having to replacing the tree. Multiple diverter assembly embodiments are also described.

Abstract: A subsea well tubular member has an axial passage with upper and lower retrievable plugs releasably mounted in the passage, the plugs having ends facing each other. A cavity is formed on one of the ends of one of the plugs. A movable barrier is mounted sealingly over the cavity, the barrier being movable repeatedly between inner and outer positions in response to temperature changes. The inner position reduces a volume of the cavity and increases a volume of a trapped fluid space between the ends of the plugs. The outer position increases the volume of the cavity and decreases the volume of the trapped fluid space. The barrier has two metallic layers with different coefficients of expansion.

Abstract: A running tool sets and pressure tests a bridging hanger and a packoff in a single trip. The running tool has a stem, an inner body, and a piston. The inner body is connected to the stem so that rotation of the stem relative to the inner body will cause the stem to move longitudinally. The piston is connected to the stem so that the stem and piston rotate and move longitudinally in unison. A piston engagement element is housed in the inner body and is adapted to engage the piston when the bridging hanger is set to prevent premature setting of the packoff. The piston engagement element can be disengaged once the bridging hanger is set, thereby allowing the piston to set the packoff.

Abstract: An alignment system can include at least one alignment device positioned between two flanges, the alignment device having a greater thickness on one side of the alignment device than on an opposite side of the alignment device. A method of producing a relative angular offset between a first flange and a second flange can include positioning at least one alignment device between the first and second flanges, and securing the alignment device between the first and second flanges, thereby producing the angular offset. A method of aligning an axis of a blowout preventer stack with a rig floor can include positioning at least one alignment device between a first flange, and a second flange of the blowout preventer stack; and securing the alignment device between the first and second flanges, thereby producing an angular offset of the second flange relative to the first flange.

Abstract: A utility skid tree system for subsea wellheads enables a tree to be mounted by and interface with utility skids. Production bore access is provided through an extended production wing block. The system reacts and transfers installation loads and potential snag loads to the conductor. The tree accepts skids for flow boosting, metering, water-oil separation, etc. A conventional choke may be fitted outboard of the utility insert profile.

Abstract: A subsea wellhead assembly provided over a wellbore, the assembly having a wellhead housing, a tubing hanger in the housing, a production tree on the wellhead housing above the tubing hanger, and a control circuit that passes axially downward from the production tree and through the tubing hanger. A tree stab assembly may be included that is set between the tubing hanger and production tree. The wellhead assembly can also include a casing hanger landed in the housing, casing attached to the casing hanger, and tubing attached to the tubing hanger.

Abstract: A subsea connection apparatus to allow connecting a surface blowout preventer stack and riser to a subsea wellhead is disclosed. The subsea connection apparatus uses a single cavity blowout preventer with a set of shearing blind rams. Hydraulically actuated wellhead connectors are secured to the top and bottom of the blowout preventer to allow connection to a subsea wellhead below the subsea connection apparatus and a well head hub profile on the lower end of a riser above the apparatus. A control system can operate both of the hydraulically actuated connectors and the blowout preventer independently. A frangible bore protector is disposed in the bore of the blowout preventer to protect the shearing blind rams from pipe, tools, and fluids being passed through the blowout preventer and can be sheared by the shearing blind rams along with any drill pipe in the bore.

Abstract: A subsea wellhead assembly includes an outer wellhead member with a bore containing at least one conical generally upward facing load shoulder that inclines relative to an axis of the bore. The outer wellhead member also contains an overpull recess having a generally downward facing overpull shoulder positioned below the at least one generally upward facing load shoulder. An inner wellhead member is lowered into the housing, the inner wellhead member having at least one conical downward facing load shoulder that inclines relative to an axis of the bore. A load ring has an inner profile that slidingly engages the downward facing load shoulder and an outer profile that slidingly engages the upward facing load shoulder.

Abstract: A variable buoyancy subsea running tool for use with subsea transportable devices, such as a tree cap. The buoyancy of the running tool may be varied through fluid or gas displacement in one or more containers. Alternatively, the running tool may be configured with a buoy that has static buoyancy, with the buoyancy of the running tool being varied through the addition of a counterweight. The running tool can be used to install or uninstall a tree cap on a subsea tree. Installation of a tree cap may be actuated by a remotely operated vehicle. Additionally, the running tool may be moved by a remotely operated vehicle and may have additional features such as a position locator device.

Abstract: An internal tree cap having a running configuration and a latched configuration to be selectively secured to a tree spool. The tree cap may include an inner sleeve movable between upper and lower positions. The movement of the inner sleeve to the lower position may simultaneously engage a locking profile within the tree spool and energize a sealing element around the exterior of the tree cap. The tree cap may be a low profile tree cap that is flush with the top of the tree spool when installed. The tree cap may provide a collateral beneficial locking means to secure a tubing hanger within the tree spool. A lower housing may be attached to the tree cap to seal on the exterior of the upper neck of the tubing hanger. The tree cap may include a profile to accept a wireline plug.

Abstract: A compact, low footprint water separation system for use in subsea well operations. A subsea production tree has a vertical passage and at least one laterally extending branch. A subsea gravity separation device having a hollow toroidal body detachably is mounted around and connected to the production tree. An inlet on a first side portion of the separation device is connected to the at least one laterally extending branch of the production tree and admits production fluid. The production fluid flows through the separation device where it passes through a separation unit. After passing through a separation unit, less dense fluid is discharged through an upper outlet and more dense fluid is discharged through a lower outlet. The upper and lower outlets are positioned opposite the first side portion of the separation device.

Abstract: A running tool for coaxially setting together subsea wellhead housings, such as a high pressure wellhead housing within a low pressure wellhead housing. The tool includes a conically shaped body that is insertable within the inner most housing, a frame with a base, an axial bore and latches. The base perpendicularly rests on top of an inner housing and the latches extend from the base to connect with an outer housing. The bore is formed to accommodate the tool freely therethrough. Wedge shaped members are provided between the base and inner housing top having their wide ends contactable by the tool. Urging the tool through the bore pushes the wedges radially outward that imparts a force between the base and inner housing top in one direction. The attached latches apply an oppositely directed force onto the outer housing.

Abstract: The present invention is a method and system for supplying grease to maintain a sealed well during deployment of line, in particular braided electrical wire. The subsea grease cartridge system includes a subsea assembly; first and second grease containers filled with grease; a pump; a switch; and a restoring device to replenish grease containers. The method of operating the grease cartridge system includes: attaching first and second grease containers to the subsea assembly; applying hydraulic pressure to the first grease container; pumping the grease of the first grease container to a grease head; switching hydraulic pressure from the first grease container to the second grease container instantaneously when the first grease container becomes unable to supply grease properly; and pumping the grease of the second grease container to the grease head. The method includes replenishing containers from cartridges and switching back and forth between the filled grease containers.

Abstract: A subsea oil and gas production Christmas tree control system, serviceable by an ROV subsea, comprises an umbilical and a system controller further comprising an HPU that comprises a manipulatable subsea housing; a subsea hydraulic fluid reservoir; a motor disposed in the housing; and a hydraulic power unit disposed in the housing. Hydrocarbon production may controlled subsea by deploying a modular subsea oil and gas production Christmas tree control system using an ROV; supplying the HPU with hydraulic fluid; providing a predetermined control to a subsea Christmas tree using a Christmas tree control system component; monitoring a Christmas tree control system status; enabling a redundant Christmas tree control system component upon detection of a fault in a Christmas tree control system component paired with the redundant component; and providing status data from the Christmas tree control system to a status data receiver using a data communications link.

Abstract: A pressure mitigating device is used to reduce pressure in a void within a wellhead housing. In one embodiment, the pressure mitigating device includes two plates that define a void between them. Increased pressure in the wellhead housing causes the plates to elastically displace towards each other. The plates contact each other, limiting the displacement prior to plastic deformation.

Abstract: A subsea wellhead assembly includes a housing with a bore. A hanger is lowered into the housing, the hanger having at least one centralizing finger with a hook for engaging a corresponding hook an activation ring carried by the hanger via a shear pin. A load ring is carried on the hanger and supported initially within a recess formed on the exterior of the hanger. At the correct depth within the housing, coinciding with a shoulder on the inner diameter of the housing, the pin is sheared under the weight of the casing string and the hooks disengage to allow the load ring on the hanger to slide outward and create a path for the casing load to be transferred from the hanger to the hanger load ring, to a housing load ring, and ultimately the housing.

Abstract: A pressure relief device is used to relieve pressure in a void within a wellhead housing. In one embodiment, the pressure relief device includes a plunger having a stepped plug, wherein the plug can be fully open to allow flow from the void, restricted to allow a predetermined flow to relieve pressure, or closed to prevent flow from the void. In another embodiment, the pressure relief device includes a vacuum puller that creates negative pressure in a vessel. As fluid in the void expands, it is able to enter the space formerly occupied by the plunger. In yet another embodiment, a rupture disc is used to prevent fluid from flowing from the void, through a passage, to the wellbore. If pressure in the void exceeds a predetermined value, the rupture disc yields and allows the trapped fluid to flow to the wellbore.

Abstract: A wellhead seal assembly forms a metal-to-metal seal between inner and outer wellhead members. A metal seal ring has inner and outer walls separated by a slot. An energizing ring has a C-ring captured on its outer surface. When the energizing ring is moved further into the slot, the C-ring is forced from its pocket and engages a profile on the seal ring, locking the energizing ring to the seal assembly.

Abstract: A passive hydrocarbon containment system for containing hydrocarbons in a fluid comprises a subsea separator dome, an oil pathway in fluid communication with a hydrocarbon collector disposed within the collection dome, and a gas outlet pipe having a discharge height dimensioned and adapted in relation to the height of the oil pathway sufficient to keep a portion of the oil pathway submerged into a fluid such as seawater present in the collection dome interior void. The hydrocarbon containment system can be moored subsea and used to collect oil and gas coming out of the ocean floor. One advantage of the hydrocarbon containment system is that there are no moving parts. A further advantage is that the hydrocarbon containment system requires limited maintenance to pump out the collected oil as needed.

Abstract: A system and method to allow backup or alternate fluid flow routes around malfunctioning components using removable, modular component sets. In one exemplary embodiment, an ROV establishes a backup hydraulic flow to a BOP function by attaching one end of a hose to a modular valve block and the other end to an intervention shuttle valve, thus circumventing and isolating malfunctioning components. A compound intervention shuttle valve is provided that comprises first and second primary inlets, first and second secondary inlets, and an outlet. A modular valve block is provided that comprises a directional control valve, a pilot valve, a manifold pressure regulator, a pilot pressure regulator, stab type hydraulic connections and an electrical wet-make connection.

Abstract: A gasket test protector sleeve is provided for subsea mineral extraction equipment. The gasket test protector sleeve includes a gasket test isolation portion. The gasket test isolation portion is configured to isolate a gasket between a first tubular and a second tubular of a subsea mineral extraction system. The bore protection portion is configured to protect a first bore of the first tubular during downhole procedures.

Abstract: An anti-rotation device prevents an inner wellhead housing from rotating within an outer wellhead housing. The anti-rotation device provides cam rollers within the inner wellhead housing that wedge between opposing surfaces of the inner wellhead housing and outer wellhead housing to arrest either clockwise or counter-clockwise rotation of the inner wellhead housing. The cam rollers are circumferentially spaced apart around the inner wellhead housing.

Abstract: Methods and apparatus for diverting fluids either into or from a well are described. Some embodiments include a diverter conduit that is located in a bore of a tree. The invention relates especially but not exclusively to a diverter assembly connected to a wing branch of a tree. Some embodiments allow diversion of fluids out of a tree to a subsea processing apparatus followed by the return of at least some of these fluids to the tree for recovery. Alternative embodiments provide only one flowpath and do not include the return of any fluids to the tree. Some embodiments can be retrofitted to existing trees, which can allow the performance of a new function without having to replace the tree. Multiple diverter assembly embodiments are also described.

Abstract: A bridging hanger with an expandable anchoring mechanism lands on a casing hanger in a subsea wellhead and actuates to anchor to the casing hanger. The anchoring mechanism includes a tubular main body, and a tubular sealing sleeve. The tubular sealing sleeve is coaxial with and mounted on an exterior diameter portion of the tubular main body. The body is moveable from an upper run-in position to a lower set position relative to the sealing sleeve. The anchoring mechanism also includes a first and second locking ring, both carried by the sealing sleeve. The first locking ring engages a profile within an interior of the casing hanger in response to movement of the main body from the run-in to the set position. The second locking ring locks the tubular main body in the set position in response to movement of the main body from the run-in to the set position.

Abstract: Valve for throttling the flow rate of a fluid, distinguished in that it comprises a bolt (12), a pipe section (8) having inner dimension adapted to enclose the bolt sealingly, a groove (13) in at least one of the outer surface of the bolt and the inner surface of the pipe section, the groove providing a fluid passageway between the enclosed bolt and pipe section, an inlet port having fluid connection to an upstream end of the groove, an outlet port having fluid connection to a downstream end of the groove, and means to adjust a coaxial position of the bolt (12) relative to the pipe (8), by moving one or both of the bolt and pipe section, in order to adjust the throttling effect of the valve. System comprising valves of the invention.

Abstract: A remotely operated submersible vehicle (ROV) is used to carry a bridge plug down to a sub sea well. The ROV is operated from a surface vessel or platform and is outfitted with a submersible hydraulic pump and a manipulator arm. Additionally, the ROV is provided with a carrying rack which can support a well closure assembly made up of an inflatable bridge plug and an affixed hydraulic running tool. The bridge plug and running tool are placed into the carrying rack and operably interconnected with the hydraulic pump so that the plug element can be selectively inflated by the pump.

Abstract: An autonomous junk collecting sleeve for a riser is provided. The sleeve is constructed and arranged to be independently lowered and seated above a subsea tree section and, subsequently, raised and removed independent of the work string. The autonomous junk collecting sleeve includes a first cylindrical structure, a second cylindrical structure concentric to the first cylindrical structure and which are joined together in spatial relation at a bottom end to form an interior J-channel basket. The J-channel basket is operable to collect debris traveling up through the bottom end and over of the second cylindrical structure for deposit therein.

Abstract: A subsea wellhead assembly that includes a wellhead housing, a production tree, a tubing hanger adapted to land in the wellhead assembly inside the wellhead housing, and a bore formed through the production tree having an inner diameter greater than the tubing hanger outer diameter. A hanger adapter may be included having an annular body disposed on the tubing hanger upper surface and a flange member projecting radially outward from the annular body.

Abstract: A lubricator valve assembly adapted for connection in a pipe string for use in a well includes a tubular valve body having a bore formed longitudinally therethrough; a valve seat connected to the valve body and in communication with the bore; a valve element mounted in the bore and rotatable with respect to the valve seat between positions opening and closing the bore; an operator in connection between the valve element and a hydraulic control system, the operator moving the valve element between the open and close bore positions in response to the hydraulic control system; and a system for opening the valve element upon failure of the hydraulic system.

Abstract: A wellhead seal assembly forms a metal-to-metal seal between inner and outer wellhead members. A metal seal ring has inner and outer walls separated by a slot. A lock ring has grooves for locking the inner wellhead member to the outer wellhead member during installation. An energizing ring has a C-ring captured on its inner surface. When the energizing ring is moved further into the slot, the C-ring is forced from its pocket and engages the surface of the inner wellhead member, locking the seal assembly to the inner wellhead member.

Abstract: A system, in certain embodiments, includes a subsea tree and a tubing spool including a longitudinal bore configured to receive a tubing hanger. The tubing spool also includes a lateral flow passage extending from the longitudinal bore and configured to transfer product to the subsea tree. The subsea tree includes multiple valves each coupled to a structure positioned radially outward from the tubing spool such that the subsea tree does not block a subsea intervention connection or blowout preventer (BOP) access to the longitudinal bore.

Abstract: Methods and apparatus for diverting fluids either into or from a well are described. Some embodiments include a diverter conduit that is located in a bore of a tree. The invention relates especially but not exclusively to a diverter assembly connected to a wing branch of a tree. Some embodiments allow diversion of fluids out of a tree to a subsea processing apparatus followed by the return of at least some of these fluids to the tree for recovery. Alternative embodiments provide only one flowpath and do not include the return of any fluids to the tree. Some embodiments can be retrofitted to existing trees, which can allow the performance of a new function without having to replacing the tree. Multiple diverter assembly embodiments are also described.

Abstract: An alignment system can include at least one alignment device positioned between two flanges, the alignment device having a greater thickness on one side of the alignment device than on an opposite side of the alignment device. A method of producing a relative angular offset between a first flange and a second flange can include positioning at least one alignment device between the first and second flanges, and securing the alignment device between the first and second flanges, thereby producing the angular offset. A method of aligning an axis of a blowout preventer stack with a rig floor can include positioning at least one alignment device between a first flange, and a second flange of the blowout preventer stack; and securing the alignment device between the first and second flanges, thereby producing an angular offset of the second flange relative to the first flange.

Abstract: A pressure relief device is used to relieve pressure in a void within a wellhead housing. In one embodiment, the pressure relief device includes a plunger having a stepped plug, wherein the plug can be fully open to allow flow from the void, restricted to allow a predetermined flow to relieve pressure, or closed to prevent flow from the void. In another embodiment, the pressure relief device includes a vacuum puller that creates negative pressure in a vessel. As fluid in the void expands, it is able to enter the space formerly occupied by the plunger. In yet another embodiment, a rupture disc is used to prevent fluid from flowing from the void, through a passage, to the wellbore. If pressure in the void exceeds a predetermined value, the rupture disc yields and allows the trapped fluid to flow to the wellbore.

Abstract: The usual safety feature of oil pipes is the shut-off valve. Whenever there is a need, such a valve can be closed, and oil is prohibited from spilling into the surroundings. However, the shut-off valve may sometimes be inaccessible. It may be buried deep in the mud, or even worse, there may be no shut-off valve. Such an oil spill could prove disastrous. Fortunately, our invention would provide a solution to just such a situation. We would need to send submarine robots to the scene of the accident. These robots, controlled from the ship on the surface, would insert our specially designed hydraulic head into the pipe. This head would then seal the pipe, stopping any further oil spill.

Abstract: A hydraulic control system for controlling an external device (4) at a well installation includes a control module (2) for generating electrical and/or optical control signals. A control pod (8) receives the control signals, the control pod controlling the external device. A hydraulic line (10) links the control pod to the external device (4) for controlling it.

Abstract: A retaining apparatus, in particular an internal tree cap, for use in a wellhead having a central bore and first and second retaining means, such as a shoulder and a groove, within the bore of the wellhead. The retaining apparatus has a housing for location within the bore of the wellhead. A first engagement assembly is provided for engaging with the first retaining means in the bore of the wellhead to thereby retain the housing within the bore of the wellhead. A second engagement assembly for engaging with the second retaining means in the bore of the wellhead is also provided. The apparatus further comprises a preload assembly operable when the housing is located within the bore of the wellhead to apply a preload to the housing between the first and second retaining means. A method for retaining an assembly within a wellhead bore, in which a preload is applied between the first and second retaining means, is also disclosed.