Technical Field

The invention relates to a subsea hydrocarbon production system.

Background

Hydrocarbon production from subsea wells typically requires pipelines to be laid across the sea floor from the wells to a production platform or vessel. Risers then carry the production fluids from the sea floor to the surface. To facilitate this, a drilling and well template may be installed on the sea floor prior to drilling. The template has a structure which supports the wellhead, BOP and valve arrangements and provides guiding systems for such equipment. A template may comprise multiple well slots for supporting multiple relatively closely spaced wells. Figures 1 and 2 illustrate a drilling and well template 1 . The template 1 has a frame 2 with a protective cover 3. Before starting to drill, the protective cover 3 is removed from the frame 2. Inside the frame 2 is a manifold 4 and supporting structures 5. Mud anchors 6 for fixing the template to the sea floor are attached to the bottom of the template 1 . Tail pipes 7 extend below the template.

After completion and during production, hydrocarbons and water are transferred from the individual wells to a pipeline via the manifold. The manifold is a large structure of valves and pipes arranged to transfer the production fluids. The manifold may, for example, combine hydrocarbons from multiple wells into one flowline.

To improve efficiency, instead of using a single pipe to transport production fluids across the sea floor, a pipeline bundle may be used. A pipeline bundle comprises individual pipelines and umbilical components inside a carrier pipe. The carrier pipe is a protective tubing around the individual pipelines and components of the bundle. Figure 3 shows the end section of a pipeline bundle 8 that has been cut open to reveal the inner pipelines and components. The bundle 8 comprises two flowlines 9 with surrounding insulation 10, a water injection pipe 1 1 , a service or MEG (MoneEthylenGlycol) line 12, power and/or hydraulics 13, fibre optic or electrical signal lines 14, rollers 15 and an outer protective tubing (carrier pipe) 16. The protective tubing may sufficiently protect the pipelines to avoid trenching.

In order to decrease off-shore time and thereby reduce costs, the pipeline bundle can be connected directly to a manifold onshore and prior to delivery to the off-shore drilling location. In this case, the manifold forms part of a towhead, allowing the manifold and bundle to be towed together and deployed at a given subsea location. A.S. den Boer, E.J. Rooduyn and W.A. Barber, 22 ^nd Offshore Technology Conference (OTC), Texas, 1990, discloses an integrated towed flowline bundle production system with a manifold included in the towhead.

EP0336492 discloses a deployment scheme in which the drilling and well template is also included in the towhead, together with the manifold and attached bundle. This may reduce off-shore installation times further. However, including the template in the towhead together with the manifold can be problematic after deployment. During operation (drilling or production), the pipeline bundle will undergo thermal expansion resulting in significant tensile and compression forces, creating loads on the manifold. If the manifold is connected to the template, these loads are transferred to the template and ultimately to the wellheads.

Summary

According to a first aspect of the present invention there is provided a hydrocarbon production system deployed on a subsea. The system comprises a foundation fixed to the sea floor, a manifold, a pipeline bundle connected to said manifold, and a guiding structure coupling the manifold to the foundation. The guiding structure is configured to allow the manifold to move in a given direction relative to the foundation while substantially preventing the manifold from moving in other directions during hydrocarbon production.

The foundation can be a drilling and well template. The foundation may comprise at least one of a compressor, a pump and a separator, located on or forming part of said foundation.

The pipeline bundle can comprise a plurality of flowlines inside a protective tubing. Optionally, the guiding structure comprises one or more guideposts and respective recesses within which the guidepost or guideposts are located to facilitate reciprocating motion of the manifold.

The foundation and the manifold can be provided within a towhead.

The system may comprise one or more movable pipes, each having a first end fixed to the manifold such that the pipe is configured to move with the manifold, and a second end connected to a pipe fixed relative to the foundation. The movable pipes may be connected to the respective pipes fixed relative to the foundation by respective telescopic joints. The telescopic joints may comprise one of Polished Bore Receptacles, PBRs, Seal Bore Extensions, SBEs, and Tubing Sealbore Receptacles, TSRs.

The manifold can be arranged to move at least 1 .5 m in said given direction on a bottom structure of the foundation.

Alternatively, the system may comprise one or more flowlines each connected to a well and to the manifold, wherein the flowline or flowlines comprise a flex loop. The manifold can be arranged to move up to 50 cm in said given direction relative to the foundation.

The given direction in which the manifold is allowed to move may be substantially in a direction of primary expansion of the pipeline bundle. The direction in which the manifold is allowed to move can be the direction parallel to a longitudinal axis of the pipeline bundle at the manifold.

According to a second aspect of the present invention there is provided a hydrocarbon production system for deployment on a subsea. The system comprises a foundation configured to be fixed to the sea floor, a manifold, a pipeline bundle connected to said manifold, and a guiding structure. The guiding structure is configurable, following deployment, to couple the manifold to the foundation whilst allowing the manifold to move in a given direction relative to the foundation while substantially preventing the manifold from moving in other directions during hydrocarbon production.

The entire structure may be towable, e.g. from an onshore location.

The foundation can be a drilling and well template. The foundation may comprise at least one of a compressor, a pump and a separator, located on or forming part of said foundation.

The system may comprise a locking structure for locking the manifold in place with respect to the foundation during towing to a deployment location, the locking mechanism being releasable at the deployment location to allow activation of said guiding structure. The locking structure may comprises one or more guide posts that can be engaged with and disengaged from aligned recesses in the foundation and in the manifold. The direction in which the manifold is allowed to move can be the direction parallel to a longitudinal axis of the pipeline bundle at the manifold.

According to a third aspect of the present invention there is provided a method of deploying the hydrocarbon production system according to the second aspect. The method comprises towing the system to a deployment location, fixing the foundation to the sea floor at the deployment location, and drilling and completing one or more wells in respective well slots of the foundation. The method then comprises testing the system before starting production.

The method may also comprise engaging the locking structure during towing and subsequently, at said deployment location, disengaging it.

Brief description of the drawings

Figure 1 is a schematic diagram of a perspective view of a well template;

Figure 2 is a schematic diagram of a side view of the well template;

Figure 3 is a schematic diagram of a cross section of a pipeline bundle;

Figure 4 is a schematic diagram of a side view of a hydrocarbon production system before deployment;

Figure 5 is a schematic diagram of a side view of a hydrocarbon production system in operation according to an embodiment; Figure 6 is a schematic diagram of a top view of the embodiment;

Figure 7 is a schematic diagram of a side view of a hydrocarbon production system in a towing configuration according to an embodiment;

Figure 8 is a schematic diagram of a top view of the embodiment;

Figure 9 is a schematic diagram of a top view of a hydrocarbon production system in operation according to an embodiment;

Figure 10 is a schematic diagram of a connector;

Figure 1 1 is a schematic diagram of a top view of a hydrocarbon production system in operation according to another embodiment; and

Figure 12 is a flow diagram illustrating the steps of a method of deploying a hydrocarbon production system according to an embodiment.

Detailed description

A hydrocarbon production system deployed on a sea bed is described here and which comprises a drilling and well template (also referred to below simply as a“template”), as the foundation fixed to the sea floor, mechanically coupled to a manifold which is in turn mechanically coupled to a pipeline bundle (referred to below as a“bundle”). The manifold is connected at the termination of the pipeline bundle. The bundle comprises multiple flowlines and umbilical components inside a protective tubing. The template has multiple well slots for supporting respective wellheads. During production, hydrocarbons and water from the wells are transferred from the wellheads to the manifold and from the manifold to the bundle. The pipelines in the bundle transport production fluids across the sea floor to a production platform or vessel. The temperature in the pipelines can be controlled, for example by heating elements inside the insulation layer around the flowlines, for example to avoid build-up of wax deposits.

As the temperature of the pipelines increases after deployment (due to controlled heating and or the heating effects of produced fluids), the pipelines expand causing the whole bundle to expand. The pipelines may be heated to temperatures in the region of 100 ^S C to 160 ^S C. Expansion is relatively slow, in the order of hours. At the end of the bundle connected to the manifold, this expansion leads to a lateral force on the manifold. That is, the bundle extends and pushes the manifold in the direction which is substantially parallel to the longitudinal axis of the bundle. Cooling of the pipelines will conversely cause compression of the bundle pulling the manifold in the opposite direction.

To avoid loading the template and, in turn, the wellheads connected to and supported by the template, the system proposed here allows the manifold to move laterally to some extent, with respect to the template, in the direction of the force from the expanding bundle.

Figure 4 shows an embodiment of the production system 17 before deployment and comprises a template 18, manifold 19 and pipeline bundle 20. Only a part of the template 18 is shown in Figure 5. The template 18 comprises a pair of horizontally extending guideposts 21 (only one of which is visible in the Figure) and the manifold 19 comprises respective guiding recesses 22. Figure 4 illustrates the system before the guideposts 21 have been engaged with the recesses 22. During towing the manifold may be locked in place (illustrated in Figures 7 and 8). For this purpose template 18 has a vertically extending recess (or recesses) 23 in its bottom structure and the manifold 19 has a corresponding recess (or recesses) 24. A guidepost can be inserted into recesses 23 and 24 to lock the manifold 19 in place. After deployment, the locking guidepost is removed, for example by a remotely operated vehicle (ROV), to allow the manifold 19 to move with respect to the template. The manifold and attached bundle in Figure 4 are slid to the left to cause the horizontally extending guideposts 21 and respective guiding recesses 22 to engage.

Figures 5 and 6 illustrate the hydrocarbon production system when fully deployed. In this configuration the manifold 19 can slide a short distance (e.g. 2 m to 3 m) across the template 18 to take up expansion of the bundle 20. Preferably the manifold 19 can slide at least 1 .5 meters. The expansion of the individual flowlines in the bundle 20 can be in the range of 6 m to 7 m. However, this expansion is constrained by the protective tubing (i.e. the carrier pipe), such that the expansion of the entire bundle 20 is only about 1 m to 1 .5 m. When the temperature of the pipelines is reduced, the bundle 20 retracts and the manifold 19 slides back across the template 18. During such expansion and retraction the template 18 only experiences small frictional forces from the sliding connection to the manifold 19. The guiding structure, comprising the guideposts 21 and the recesses 22, allows the manifold 19 to move laterally in one direction while also substantially prohibiting motion in other directions (e.g. vertically). The horizontal direction along which the manifold 19 is free to move is substantially aligned with the longitudinal axis of the bundle 20, i.e. with the direction of primary expansion. This is important, as any tangential forces from the bundle 20 on the manifold 19 will also load the template 18 through the guideposts 21 .

Figures 7 and 8 illustrate the hydrocarbon production system 17 during towing, with the manifold 19 locked to the template 18. The vertical recesses 23 in the bottom structure of the template are aligned with the recesses 24 of the manifold, and guideposts 25 (i.e. locking pins) are inserted into the recesses. The locking pins 25 prevent the manifold 19 from sliding on the template 18 (horizontally), while the horizontal guideposts 21 of the guiding structure prevent the manifold 19 from moving vertically.

In the embodiments illustrated in Figures 4 to 8, the guiding structure comprises a pair of guideposts 21 fixed to the template 18 and respective guiding recesses 22 in the manifold 19. In other embodiments, the guiding structure may comprise one or more guideposts fixed to the manifold 19 with respective recesses in the template 18.

Upon deployment on the seabed, the manifold 19 must of course be connected to the various wellheads supported by the template 18. Figure 9 illustrates an installation configuration in which the manifold 19 is connected to four wellheads (not shown) via four respective connectors 26. To allow for the movement of the manifold 19, each connector 26 comprises a telescopic joint 27 (also known as a slip joint) mounted within a stuffing box 28. The telescopic joint 27 may be a polished bore receptacle (PBR) or an expansion joint such as a sealbore extension (SBE) or a tubing sealbore receptacle (TSR). The connectors 26 connect pipes 29 fixed to the manifold 19 (“moving pipes” 33) to pipes 30 fixed to the wellheads (“fixed pipes” 34). The moving pipes 29 move with the manifold 19 as the bundle 20 expands and retracts, while the fixed pipes 30 remain in place.

Figure 10 illustrates an embodiment of the connector 26 comprising a telescopic joint 27 (e.g. a PBR) inside a stuffing box 28 inside a pressure container 31 . A pressure sensor 32 and temperatures sensor 33 are fitted into the wall of the container 31 . The container 31 is kept marginally above the ambient (i.e. surrounding) pressure and contains a corrosion inhibitor and lubricant. The container 31 also provides protection from seawater, scale etc. It seals the flowlines 29 and 30 with a fixed seal 34 in the end on the well side, and a dynamic seal 35 in the other end on the manifold side. The container 31 can also be used to collect leaked oil and/or gas from the joint 27 using, for example a bilge system with a pump. A displacement pump can be used to cater for both liquids and gases. The connector may also comprise a local heat source to prevent the seals from seizing up.

As an alternative to the use of telescopic joints to facilitate guided movement of the template 18 and the manifold 19, the movement of the manifold 19 may be taken up by “flex loops” 36 between the wells (i.e. the xmas tree attached to each wellhead) and the manifold 19. Figure 1 1 illustrates this embodiment with four connections 37 (flowlines) from the manifold to the well slots (not shown). Each flowline 37 comprises a section of flexible spool piping 36 (i.e. flex loops). The maximum expansion that may be compensated for is approximately 50 cm.

In an alternative configuration, a sliding sleeve or slip joint arrangement for the flowlines in the bundle connected to the manifold may be used, while the carrier pipe is close to motionless. This configuration uses a sliding sleeve with lubricator valve / stuffing box and outer containment to maintain two barriers. It requires changes to the existing bulkhead design at the end of the bundle, which cannot be welded. The maximum achievable expansion is some 3 to 4 meters. Different expansion of the flowlines and the carrier pipe are dependent on different design solutions and on the interaction between the flowlines and the carrier pipe.

Figure 12 is a flow chart illustrating a method of deploying the hydrocarbon production system. The method comprises towing a hydrocarbon production system to a subsea location S1 and fixing the template to the sea floor at the subsea location S2. The template is now ready for drilling operations and risers from the host facility (e.g. production platform) are tied in to a manifold at the other end of the bundle. The method also comprises drilling and completing one or more wells in respective well slots of the template S3, and testing the system before starting production S4.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention. For example, whilst the invention has been described above in the context of a drilling and well template, the invention may be applied to other seabed foundations to which a manifold and pipeline bundle are attached. The foundation may be, for example, a foundation supporting hydrocarbon processing apparatus such as subsea compressors, separators, etc. The pipeline bundle terminates at the manifold, which in turn is coupled to the foundation fixed to the seabed. The manifold is hence connected to the end-point of the pipeline and is pushed and pulled by the thermal expansion and contraction of the pipeline during production.