Abstract: A method of constructing a sliding subsea foundation includes embedding at least one mass of rocks in seabed soil and placing a sliding mudmat on the seabed over the or each mass of rocks. The rocks can be lowered into a cavity in the seabed by dumping the rocks into the cavity or when contained within a gabion that is inserted into the cavity. Alternatively, a gabion containing the rocks can penetrate the seabed soil, driven by self-weight or additionally by a deadweight bearing on the gabion. The gabion can be lowered toward the seabed suspended from the deadweight. The deadweight can be removed and recovered after the gabion has been embedded in the seabed. The mass of rocks is embedded within an area of excursion of the mudmat to ensure that the mudmat will lie directly above the mass of rocks at any position within the area of excursion.

Abstract: A technique mitigates or removes a plug of solid-state material such as wax or hydrate coalesced from hydrocarbon fluids in a subsea flowline pipe. In a normal flow mode, a flow of hot production fluids directed from a subsea well into a production flowline pipe extending toward a processing or storage location. Simultaneously, a contra-flow of service fluid such as monoethylene glycol (MEG) is transported along a service fluid pipe extending along and adjacent the production flowline pipe. The service fluid is injected into the well or flow of production fluid upstream of the flowline pipe. On determining plugging or a risk of plugging of the flowline pipe, a heating mode is activated wherein at least some of the flow of the production fluid is diverted into the service fluid pipe. This heats the service fluid pipe which, in turn, heats the flowline pipe to disperse the solid-state material.

Abstract: A protective subsea housing for protecting an equipment space enclosed by the housing has an access opening in a wall of the housing for providing access to the equipment space by an unmanned underwater vehicle (UUV). The housing has a closure that is movable by translation, or by rotation relative to an axis transverse to or extending through the wall, to open and close the access opening, and an operating member, such as a rotary coupling, that is positioned outside the equipment space and is engageable and movable by the UUV to move the closure.

Abstract: A modular subsea fluid storage unit comprises a variable-volume inner tank having a rigid top panel and a peripheral wall that is flexible by virtue of concertina formations. The peripheral wall is extensible and retractable vertically while the horizontal width of the tank remains substantially unchanged. A side wall of a lower housing part surrounds and is spaced horizontally from the peripheral wall of the inner tank to define a floodable gap between the peripheral wall and the side wall that surrounds the tank. An upper housing part extends over and is vertically spaced from the top panel of the inner tank and overlaps the side wall to enclose the inner tank. The floodable gap and the upper housing part enhance thermal insulation and trap any fluids that may leak from the inner tank.

Abstract: A modular subsea fluid storage unit has a variable-volume inner tank having a rigid top panel and a peripheral wall that is flexible by virtue of concertina formations. The peripheral wall is extensible and retractable vertically while the horizontal width of the tank remains substantially unchanged. A side wall of a lower housing part surrounds and is spaced horizontally from the peripheral wall of the inner tank to define a floodable gap between the peripheral wall and the side wall that surrounds the tank. An upper housing part extends over and is vertically spaced from the top panel of the inner tank and overlaps the side wall to enclose the inner tank. The floodable gap and the upper housing part enhance thermal insulation and trap any fluids that may leak from the inner tank.

Abstract: A subsea processing system has a lattice frame made up of structural members and at least one fluid-processing device. At least one of the structural members effects fluid communication to or from the or each fluid-processing device.

Abstract: An underwater turbo-generator unit for producing electrical power has a pressure-resistant shell that defines a sealed internal chamber. At least one water inlet extends through the shell to effect fluid communication between the chamber and a body of water surrounding the shell. A turbine is supported within the chamber to turn on a spin axis in response to admission of a flow of water into the chamber via the or each water inlet. The shell is arranged to maintain a gas-filled space within the chamber, facilitating the use of a Pelton turbine that turns about a vertical spin axis. The or each water inlet communicates with at least one tubular penstock structure that can be supported by the unit outside the shell. The chamber communicates with, and drains water into, a fluid storage volume such as a pipeline positioned at a level beneath the chamber.

Abstract: A pig diverter comprises a hollow housing having a flowline inlet port, a flowline outlet port, a pig entry opening, and a pig exit opening, all communicating with the interior of the housing. A tubular pig holder enclosed by the housing is pivotable between a receiving position and a launching position. In the receiving position, the pig holder is aligned with the pig entry opening to receive a pig and effects fluid communication between the pig entry opening and the flowline outlet port. In the launching position, the pig holder is aligned with the pig exit opening to launch a pig and effects fluid communication between the flowline inlet port and the pig exit opening.

Abstract: A subsea production unit for subsea treatment of oil has a frame that supports an onboard multiphase separation system for separating gas and water from a wellstream containing oil. The subsea production unit also includes an onboard water treatment system for cleaning oil from water that is produced by the separation system.

Abstract: A method of installing an upright elongate hollow subsea foundation that is higher than it is wide, such as a suction pile. The foundation is at least partially embedded in seabed soil. A partition layer is placed within the foundation, for example by injecting a grout, supported by a plug of soil that is surrounded by the foundation. The partition layer is placed on the plug of soil at a level that is spaced from the top of the foundation by at least 20% of the height of the foundation. Above the partition layer, the interior of the foundation may be filled with water and/or a rigid body, such as a solid mass or a hollow liquid-filled tank.

Abstract: A subsea multiphase fluid separation system has a gas separator for separating gas from a well stream containing oil. A water separation stage downstream of the gas separator has at least one dual pipe separator for separating water from the oil of the wellstream. A water treatment system for cleaning oil from water is produced by the water separation stage. On an oil outlet path, downstream of the or each dual pipe separator, there is an electrocoalescer and at least one second separator in series.

Abstract: A method of sanitising seawater at a subsea location comprises: exposing flow of seawater in a treatment reactor to UV radiation that sanitises the seawater without the addition of sanitising chemicals; and outputting the sanitised seawater from the reactor into a subsea structure such as a pipeline or a wellhead. The flow of seawater may be exposed to successive emitters of UV radiation such as pressure-compensated LEDs. The efficacy of sanitisation may be determined by: injecting a tracer fluid into the flow of seawater upstream of the reactor; and, downstream of the reactor, sensing transformation of the tracer fluid due to exposure of the tracer fluid to the UV radiation in the reactor.

Abstract: A subsea hydrocarbon export system includes a riser tower having a riser column extending from a seabed location to a sub-surface buoy that supports the riser column in an upright orientation. A subsea connector is operable underwater to couple the riser column temporarily to a hose suspended from a surface shuttle tanker vessel for an export operation and to release the hose after the export operation.

Abstract: A drilling conductor supported within a suction anchor is installed by lowering the suction anchor through the top of a frame of a subsea processing unit. The base of the frame defines a landing area for the suction anchor and supports a fixing system for fixing the suction anchor to the frame. When the suction anchor has been embedded into the seabed beneath the processing unit, the frame is fixed to the suction anchor to form a structural unit that includes the conductor, the suction anchor and the frame. Additional equipment such as a blow-out presenter or a Christmas tree is lowered through the top of the frame and onto the conductor that is supported by the embedded suction anchor.

Abstract: A compact subsea pig launcher comprises a tubular magazine for holding a plurality of pipeline pigs in longitudinal succession ready for launching successively into a subsea pipeline. The magazine is shaped to define at least one turn such as a coil around an upright axis. Thus, a series of pigs are stored in longitudinal succession along a path that is curved in plan view around the upright axis. During launching, at least one of the series of pigs is advanced along the path with angular movement around the upright axis.

Abstract: An injection fluid is pressurized for injection into a subsea installation or equipment by using a flow of hydrocarbon production fluid to draw the injection fluid from a source and using pressure of the production fluid to pressurize the drawn injection fluid to an elevated pressure. In response to an ejector that is powered by the flow of the production fluid, a pressure booster draws in the injection fluid for pressurization. A portion of the production fluid is diverted to the pressure booster to pressurize and expel the injection fluid and is then exhausted to the ejector as more injection fluid is drawn in.

Abstract: An offloading system for conveying hydrocarbons from a buoyancy-supported subsea riser to a surface tanker vessel comprises a flexible hose that hangs from the riser structure in a U-shape having first and second limbs. An upper end of the first limb communicates with the riser and an upper end of the second limb terminates in a pulling head for connecting the hose to the tanker. A clump weight acts on a lowermost bend of the hose between the limbs to maintain tension in the limbs. A subsurface holder fixed to the riser structure is arranged to hold the pulling head against the tension in the second limb of the hose when the system is in a standby state. The holder is offset laterally from a central longitudinal axis of the riser structure and a counterweight is positioned to a side of that axis opposed to the holder.

Abstract: A subsea energy storage installation comprises a pumped-storage system having pumping and hydropower generation components for, selectively, converting electricity into potential energy by expelling water from within a tank into the surrounding sea and for generating electricity from an incoming flow of water re-entering the tank under hydrostatic pressure. The tank comprises at least one elongate rigid pipeline that may be lowered to the seabed as part of a towable unit or laid on the seabed as a pipe string launched from a surface vessel.

Abstract: A multiple pig launcher includes a tubular structure along which a series of pipeline pigs may be advanced in stepwise fashion to be launched into a pipeline in succession. A launching station holds a first pig at a downstream end of the series in readiness for launch. A pig stopper mechanism is operable selectively to hold a second pig at a holding station upstream of the launching station when launching the first pig and to release the second pig from the holding station to be advanced into the launching station after the first pig has been launched. The pig stopper mechanism comprises at least one radially movable gripper element that can apply radially inward gripping force to a pig held at the holding station.

Abstract: A wax control element for subsea processing of well fluids in a wellstream comprises a bundle of flowlines within an elongate tensile structure. That structure defines inlet and outlet ends and has cooling and heating provisions that act on the flowlines, in use, to promote deposition of wax in the flowlines and subsequent entrainment of wax in the wellstream.