GAS STORAGE SYSTEM

Abstract

A portable subsea storage tank for the storage of gas products under pressure or oil products consisting of pipeline sections in an array which can be coated in specialist coatings and recovered for inspection and re-use. A method of self-installing the subsea storage tank is also described.

Claims

1. A portable subsea storage tank for the storage of gas products under pressure or oil products comprising: an array of pipe members, the pipe members connected together and configured to contain a fluid for storage; a framework to hold the pipe members in the array; a hull supporting the framework and providing transportation of the storage tank to and from a quayside to a location on the seabed and subsequent re-use at different locations; ballast capacity to control the descent/ascent of the storage tank; and an anchoring arrangement to hold the storage tank in position to the seabed.

2. The portable subsea storage tank according to claim 1 wherein the pipe members are formed from a plurality of pipe sections which are connected by at least one pipe bend of minimum 60°.

3. The portable subsea storage tank according to claim 2 wherein the plurality of pipe sections are connected together as a continuous long section comprising of multiple turns to form a total length of at least double that of a length of the storage tank.

4. The portable subsea storage tank according to claim 2 wherein the plurality of pipe sections are connected one to another with a conduit, the conduit having a smaller diameter than the pipe sections.

5. The portable subsea storage tank according to claim 1 wherein the framework includes connection means for installation of a pig launcher at a first location on the array and a pig receiver at a second location on the array to allow pipeline inspection, cleaning and flushing activities to be performed.

6. The portable subsea storage tank according to claim 2 wherein one or more of the pipe sections include separate internal storage cylinders of at least one non-metallic high strength material to contain gas under high pressure.

7. The portable subsea storage tank according to claim 1 wherein the portable subsea storage tank includes a pipework manifold comprising a plurality of valves to control the distribution of the fluid through the array.

8. The portable subsea storage tank according to claim 1 wherein a plurality of dynamic risers are attached to the storage tank to allow the passage of fluids and an umbilical to provide command and control to mechanical and electrical systems on the framework.

9. The portable subsea storage tank according to claim 2 wherein the pipe sections are heavy walled pipe sections, sufficient to avoid floating in seawater when empty.

10. The A portable subsea storage tank according to claim 2 wherein the pipe sections have an outside diameter between 0.30 m to 1.5 m.

11. The portable subsea storage tank according to claim 10 wherein the pipe sections have an outside diameter between 30″ to 40″ (0.762 m to 1.016 m).

12. The portable subsea storage tank according to claim 1 wherein the array is 10 m to 250 m in length along parallel arranged pipe members.

13. The portable subsea storage tank according to claim 1 wherein the pipe members are arranged side by side and on top of each other to provide a three dimensional array.

14. (canceled)

15. (canceled)

16. (canceled)

17. (canceled)

18. (canceled)

19. The portable subsea storage tank according to claim 1 wherein the anchoring arrangement is selected from a group comprising: suction anchors, driven piles, drilled piles, ballast weight and mooring lines.

20. A method of self-installing a portable subsea storage tank comprising the steps of: (a) providing a portable subsea storage tank comprising: an array of pipe members, the pipe members connected together and configured to contain a fluid for storage; a framework to hold the pipe members in the array; a hull supporting the framework and providing transportation of the storage tank to and from a quayside to a location on the seabed and subsequent re-use at different locations; ballast capacity to control the descent/ascent of the storage tank; and an anchoring arrangement to hold the storage tank in position to the seabed; (b) floating and towing the portable subsea storage tank to a desired location; (c) adjusting ballast capacity on the subsea storage tank to thereby submerge the subsea storage tank; (d) anchor the subsea storage tank to the seabed; and (e) introducing a fluid into the pipe members of the subsea storage tank to store the fluid.

21. (canceled)

22. The method of self-installing a portable subsea storage tank according to claim 20 wherein the method includes the steps of adjusting the ballast capacity to re-float the storage tank and towing the storage tank to a further location.

23. The method of self-installing a portable subsea storage tank according to claim 20 wherein the method includes the step of inspecting the pipe members by using a pipeline pig.

24. The method of self-installing a portable subsea storage tank according to claim 20 wherein the gas is hydrogen under pressure produced from renewable sources.

25. The method of self-installing a portable subsea storage tank according to claim 20 wherein the gas is carbon dioxide under pressure and the method includes the step of injecting the gas into sub-surface reservoirs.

26. The method of self-installing a portable subsea storage tank according to claim 20 wherein the method includes the step of offloading stored fluids to a transportation vessel via exchange of fluids to maintain the gas under the same pressure when moving from the tank to the transportation vessel.

Description

[0071] Reference is initially made to FIG. 1(a) of the drawings which illustrates a subsea storage tank, generally indicated by reference numeral 10, as a floating structure comprising an array of pipe stalks or pipe members 14, a framework 16 to hold the pipe sections 14 in the array, a hull 12 to support the array 14 and a ballasting capacity 18 in the form of towers, according to an embodiment of the present invention.

[0072] FIG. 1(a) shows a cross-section through a typical floating structure as it is resting in position on the seabed 28. The main part of the hull 12, supports the rest of the equipment above. The pipe stalks 14 are arranged longitudinally on the deck to maximise their length and are secured in position at intervals by supports 16 which must also allow the stalks 14 to expand when pressurised.

[0073] The barge can be alongside a quay or in dry-dock to allow the construction of the stalks together with the appropriate physical supports, valving and isolations to match the functional requirements.

[0074] The descent to the seabed is controlled by the towers 18 which adjust the buoyancy of the structure, especially when the pipe stalks are submerged, to keep the structure level. The descent is controlled by taking on small quantities of ballast in the towers and hull 12, ensuring the centre of gravity is well below the centre of buoyancy and using a mooring system to control the descent. Such a mooring system is described in WO2017168144, the contents of which are incorporated herein by reference.

[0075] The structure is anchored in position on the seabed by skirts or suctions anchors 20. The stalks are connected via jumpers 34 to a distribution module 21, which through valving controls the pressurisation and depressurisation of the stalks from a production facility or to a transportation vessel. The flowline or pipeline 32 between the various other facilities in the field together with the power and controls function umbilical 30 exit the structure.

[0076] The FIG. 1(b) shows the side elevation of the same structure showing the bulwarks 22 along the side of the structure, which gives the arrangement additional rigidity and strength. During deployment and recovery there are holes in the bulwark 25 which are standard mooring chocks, which allow water to freely pass onto the main deck during submergence and drain during recovery. The bulkwarks may optionally extend up above the top level of the pipe stalks to give additional protection.

[0077] This figure shows the structure anchored by piles 24, which are lowered through the tower; however any point on the structure can be chosen as an anchoring point, including on the outside of the structure. The piles are shown sticking up and hence do not need to be cut post installation.

[0078] An alternative route for contents to flow and power/controls to exit or entry the structure is via a dynamic riser 38, which is shown with distributed buoyancy modules 36. This typically would rise up to a floating vessel and the structure provides a base for such riser systems.

[0079] FIG. 2(a) shows the structure in plan view, showing the pipe stalks 14, in this case arranged in a U shaped configuration, with additional pipework providing the ‘U’ to join pipe members 14, the supports 16, including a longitudinal support on the right hand side, towers 18, distribution module or manifold 21 and bulwarks 22.

[0080] The passage of contents, power and controls is shown in the pipeline 32 and umbilical 30. The passage of fluids from the distribution module or manifold to the pipe members is managed by jumpers 34, which also may have valves to control the distribution and allow isolation of each pipe member.

[0081] FIG. 2(b) shows an end view in cross-section of the structure, showing the array arrangement of pipe stalks 14 and bulwark 22. The array is three dimensional but may be two dimensional, though this would provide significantly less storage space. In this embodiment both suction anchors 20 and piles 24 are shown.

[0082] The pipe stalks 14 are made up of pipe sections which are internally coated and welded together. Typically for pressures in the region of 150-250 barg (1 barg=100 kPa above atmospheric pressure) pipes with outside diameters in the region of 30″ to 40″ have a wall thickness and steel grade which is commonly available. Pipes offer a well proven and simple to build option with the key advantage that the fabrication into long stalks up to and in excess of 100 m can be performed onshore at low cost. The pipes are of such a diameter that they can easily be internally coated, including the welded joint and inspected. The pipe internal coating integrity is a key aspect to protect against the risks of internal and external corrosion. By using a structure composed of preferably standard line pipe sizes, welded together and coated using standard industry and well established practises, manufacture and costs are simplified. The pipes are welded together to form ‘stalks’ or pipe members which should be as long as possible in order to minimise the number of valves, flanges and connections.

[0083] FIG. 3(a) shows the structure 44, tank 10, lowered into a man-made excavation 42 in the seabed 28. This provides greater protection from wave and currents and has backfill material 40 in the void spaces between the structure and the side of the excavation. The backfill may be deployed by a vessel and/or be natural backfill.

[0084] FIG. 3(b) show the structure 40 fully contained within a ‘glory hole’ 46. This is typically used in iceberg prone areas such as Newfoundland.

[0085] FIG. 4(a) shows a plan view of an array of stalks in a continuous horizontal loop with supports 16. The end of the loops 52 and 54 consist of bends in the vertical orientation to potentially connected to an identical loop on the next layer. Such a loop can be pigged providing suitable bend radii are specified. Alternatively, the ends can be connected to a pig launcher and receiver to allow inspection of the pipe internals using standard techniques and equipment employed in the pipeline industry.

[0086] FIG. 4(b) shows a plan view of an array of stalks in their simplest configuration of straight sections 56 with flanges 58 at each end with underlying support 16. Connectivity between each of the straight sections can be provided with a hose or smaller bore pipework 60 between each stalk.

[0087] FIG. 5(a) shows a side view of an offshore structure which has an array of stalks 66 in the base of the jacket structure 64, 68. A topsides 62 is provided on the structure and buoyancy is provided for the structure by virtue of large diameter legs 68, to enable the structure to float to site and be lowered in a controlled manner by flooding of the legs.

[0088] FIG. 5(b) shows a plan view in cross section of the structure in FIG. 5(a) showing the array of stalks.

[0089] FIG. 5(c) shows a side view of an offshore structure which has an array of stalks 76 arranged in a vertical orientation, in the base of the jacket structure 74, 78. A topsides 72 is provided on the structure and buoyancy is provided for the structure by virtue of large diameter legs 78, to enable the structure to float to site and be lowered in a controlled manner by flooding of the legs.

[0090] FIG. 5(d) shows a plan view in cross section of the structure in FIG. 5(c) showing the array of stalks.

[0091] FIG. 6(a) shows a side view of an offshore structure 80, which has a topsides 82 jacket structure 86 and array of stalks 88 in the lower section, resting on a base 96. The array of stalks has a dropped impact protection structure 92 above the array of stalks. The structure is affixed to the seabed 94, through piles 90.

[0092] FIG. 6(b) shows a plan view in cross section of the arrangement of the array of stalks 88 of FIG. 6(a), together with the stalk supports 96. The surrounding jacket structure 86 is shown together with the pile guides 90.

[0093] FIG. 7 shows a cross section of a vertical stalk 108. The stalk is lowered into a pre-drilled casing 102 in the seabed 100. The stalk has a sealed bottom end 110 and two ports at the top end to allow venting 112 and draining 104 on a blind flange 106. The drain line is small bore tubing to remove any liquids within the stalk.

[0094] FIG. 8 shown an elevation of the underwater gas storage structure 124 under tow by a tug or anchor handling vessel 120, using a two line. Equally there may be a trailing tug to control the structure. Such arrangement is typical of the methodology employed to tow structures, barges and vessel in the ocean and illustrates its applicability for the invention.

[0095] FIG. 9 shows a cross section view of a typical pipe member 134, which is a straight section with no bends, in which an internal storage cylinder 132 of high strength material, for example carbon fibre, is inserted. The pipe member is shown here with a blind flange 144 on end and a blind flange with two ports 142. The fluids are supplied via a port and valve 136 directly into the internal cylinder. The void space 138 between the cylinder and the pipe member is held under a pressure to minimise the stresses on the pipe member and the cylinder, by acting to counteract the internal pressure within the cylinder. This void space pressure can be controlled by the pressure regulator valve 140, which acts as a monitoring valve in the event of a slow leakage from the internal cylinder and a pressure relief valve in the event of a more rapid leak or rupture of the cylinder. The valve 140 leads to pipework to manage the release as part of the overall subsea storage tank arrangement.

[0096] By this means the system becomes re-usable, largely self-installing and uses well established pipeline maintenance and inspection techniques to provide a reliable large buffer storage of gas offshore. Onshore inspection of the whole arrangement is also possible to inspect the internal coating and facilitate repairs as required.

[0097] In use, the pipe members/stalks will be arranged on a floating structure which can be towed out to location and sunk in a controlled manner onto or into the seabed, where it can be fixed in position for the operation duration. At the end of the operational duration the arrangement can be de-ballasted and re-floated to the surface for tow to a location where it can be inspected, cleaned and made ready for the next deployment. The system is intrinsically safe, as being under the water there is no ignition source of oxygen nearby.

[0098] The system is therefore designed to be re-usable, largely self-installing and built using existing proven fabrication methods, combining pipeline technology with submersible barge technology to facilitate the use of specialist coating to address the technical challenges of hydrogen and carbon dioxide storage.

[0099] The installation and recovery will follow the principals of prior art WO2017168144 to control the heading and position on the seabed by using a number of pre-installed mooring lines which will be connected to the structure prior to submergence to accurately locate on the desired position on the seabed. As stated there may be parts of the structure which do not fully submerge but these perform a secondary role to the storage system.

[0100] The floating structure when on the seabed can also act as a host for a variety of other functions, such as containing additional liquids or gases, acting as a manifold, act as a base for static flowline connections and/or dynamic riser, sub-sea isolation valve, etc.

[0101] The gas is generally stored under pressure the pressure dictated by the types of gas and a compromise between the storage volume achievable vs the economics. While hydrocarbons both as pressurised gas and liquids i.e. oil can be stored, the tank can also be used to store hydrogen, ammonia or any other compound with an industrial use.

[0102] By having control of pressure, the storage tank can be used for offloading stored fluids to a transportation vessel via exchange of fluids to maintain the gas under the same pressure when moving from the tank to the transportation vessel.

[0103] When deployed, the pipe stalks should preferably be arranged to minimise the number of horizontal sections where liquids could pool, plus there should be drains at the low points of the pipes and vents at the high points of each stalk. Indeed, while the figures illustrate stalks arranged in horizontal and vertical orientations, the pipe stalks may be arranged at an angle to the seabed.

[0104] The stalks may be connected together to form a larger loop comprising bends. These bend preferably should be sizes to allow ‘pigging’ of the storage system at intervals to condition, inspect and as required clean the internals.

[0105] The structure can be anchored by any of the anchoring methods used subsea, such as suction anchors, driven or drilled piles, ballast weight or even mooring lines which are anticipated to be used to control the descent of the structure onto the seabed.

[0106] The stalks may also be lowered into pre-drilled holes in the seabed, such holes being made by standard offshore drilling equipment. This gives the advantage that the stalk length is only limited by the length which can be upended to lower into the hole or increased further by provision of a pipe fabrication system on-board the drilling vessel to assembly more sections together. In this way the lengths of the stalks is only limited by the practical depth to drill down and consideration of the geology of the area in the stability of the underlying substrate. The stalk may also be cemented in-place to provide additional stability.

[0107] This invention therefore provides apparatus and a method of maximising the length of an internally coated mobile and re-useable pipeline without the length restriction on onshore fabrication or high cost of fabrication offshore. By arranging the pipe joints in an interconnected array of pipes they can be welded onshore and a single long length which is still transportable as a single unit within a ballast-able sea-going barge or vessel or as part of another submergible subsea structure. The invention by its nature also allows full internal coating of the array pipes to minimise or prevent corrosion including the use of more exotic lining materials, not normally considered for offshore use due to the time to apply and strain applied during traditional installation. Further the structure being re-deployable can be fully inspected alongside a quayside and repaired or modified as required for subsequent deployments. It can also be inspected offshore, since by provision of a pig launcher at one end and a pig receiver at the other end the pipe array can be inspected and/or cleaned/flushed in the same procedure as for a long offshore pipeline.

[0108] The array pipes generally should not be used as the means of installation of the arrangement, since the flooding of the array pipes with seawater bring about serious issues of corrosion, cleanliness and dryness which if not managed can lead to hydrate formation and accelerated corrosion. Thus the system uses a separate ballasting system, leaving the array pipes core functionality as being the fluids, notably gas, storage. To allow cleaning and internal inspection of the array pipes the interconnectivity with large diameter bends allows the passage of cleaning/inspection systems such as “pigs”. Furthermore, for large diameter pipe arrays internal inspection and repairs by human or robotic intervention is possible.

[0109] The integration of readily available pipe sections into a long continuous loop within a submersible structure which complies with maritime regulations for a towed vessel or barge provides an advantageous storage arrangement.

[0110] The principal advantage of the present invention is that it provides an underwater or subsea storage tank for the storage of gas products under pressure or oil products.

[0111] A further advantage of at least one embodiment of the the present invention is that it provides an underwater or subsea storage tank using standard line pipe and allowing more advanced welding and/or coating techniques.

[0112] A yet further advantage of the present invention is that it provides an underwater or subsea storage tank which is re-useable, unlike a laid pipeline.

[0113] A still further advantage of at least one embodiment of the present invention is that it provides an underwater or subsea storage tank which can be used as a host-subsea structure for other applications such as a manifold, riser base, tie-in point or SSIV (subsea safety isolation valve module).