TECHNICAL FIELD

The present invention relates to a system and method for fluid storage at ocean bed and transportation thereof to ocean surface. More specifically, the present invention relates to storage of production fluids at ocean bed and method to access the storage thereof under extreme offshore environmental conditions, where the depth of ocean bed typically varies from shallow waters to ultra-deep waters, below the ocean surface level.

BACKGROUND ART

The world ocean covers about 71% of the earth surface, is the principal component of earth’s hydrosphere which is integral to life and influence climate & weather patterns. Rising energy or resources demand and depleting onshore resources have led mankind to explore vast oceans of our planet to meet future needs. From the early 20 ^th century, researchers from several fields are working to explore the best innovative solutions to tackle the extreme environmental challenges posed by the mighty oceans. Till the present day, though we have achieved unimaginable milestones in understanding and tackling such environmental challenges, the insufficiency in our understanding is made evident by several fatal incidents in the recent decades, which have resulted in the loss of precious human and marine life. A huge reserve of resources is believed to lie beneath the ocean water, which is yet to be explored due to non-availability of commercially viable technologies.

The technological challenges are mostly due to extreme environmental conditions of deep-water surface, huge water pressure, and very low temperature beneath the water jacket. Therefore, to justify the massive capital and operational expenses, the selected ocean field should be commercially viable for large scale implementation. The importance of accurate reservoir exploration can be deduced from this fact and therefore, the involved companies invest a substantial amount of their resources in terms of time and money for exploration of the reserves. SUMMARY

The present invention discloses apparatuses and methods for offshore production fluid storage at ocean bed and accession of stored production fluid thereof in hostile waters. The present invention incorporates a variety of systems. Major systems include the following: a. Stability system; b. Production system; c. Storage system; d. Mooring system; and e. Control & Communication system.

The stability system of field includes cylindrical corrosion resistant metallic tanks connected with each other through tie beams. The cylindrical tanks of suitable wall thickness provided for buoyancy manipulation via ballasting/de-ballasting with mud of suitable specific gravity but the invention is not limited to mud, any suitable fluid denser than ocean water has the same utility. Each cylindrical tank is connected with ballasting pipeline system comprises of pipeline network at two different levels. One network is provided at the bottom portion and other network at top portion of hollow cylindrical sections. Both the ballasting pipeline network are provided with flexible pressure tubing, from which ballasting via fluid injection can be done. In empty condition, the cylindrical tanks are able to provide sufficient buoyancy to individual components and to the whole field through which they can float on its own. During field placement process, cylindrical tanks are partially ballasted with mud which results in sinking of entire field in ocean water. Once the field reaches near ocean bed, it is properly oriented, placed and ballasted completely. The stability system of mooring ropes of subsea plant comprises of independent foundation blocks having similar large metallic cylindrical tanks and placed at ocean bed in the same manner as described above.

The production system includes pipeline network, subsea manifold and subsea umbilical termination unit. The pipeline network comprises of production pipelines and de-ballasting pipelines, provided above stability system of field fixed with subsea manifold and have NRV's and ball valves at each storage collection point which can be operated through solenoid system or hydraulically but the invention is not limited to any specific valve system. The subsea manifold collects the production fluid from all the wells and channelise it through required production pipeline. The de-ballasting pipeline network is connected to subsea booster pump through which the water at outlet of de-ballasting pipeline network after de- ballasting operation, will be injected inside ocean bed via water injection well. The electrical power requirement of various subsea equipment’s is meet out from branch umbilicals through subsea umbilical termination unit which receives it through main umbilical from control & communication system.

The storage system includes large spherical storage shells, shell resting cage, shell mouthpiece assembly and shell umbilical. The storage shells are made up of strong but light weight metallic alloys like Aluminum alloys, Titanium alloy, Steel alloys etc. whose thickness is a function of depth of operation having inner lining provided with level sensors so as to monitor and control the production fluid filling operation. However, the invention is not limited to only metallic spherical storage shells as other materials (rigid or flexible) as well as shapes (cylindrical, box, etc.) are also applicable. These storage shells utilize the difference in bulk density of production fluid inside and ocean water outside the shell beneficially for generation of positive buoyant force or via attachment of any other buoyant assembly. The storage shells are equipped with upper half of resting cage fixed on upper half portion which can be peripherally rotated about its apex point and the lower half of resting cage is fixed with cylindrical tank through metallic columns, however the locking mechanism of invention is not limited to anchoring of upper & lower cages only. The lower half of resting cage at its base is fixed with storage collection point. The peripheral rotation of upper half of resting cage about its apex leads to locking and unlocking of storage shell with lower cage against buoyant force. Locking of storage shell leads to contact of storage collection point and shell mouthpiece assembly. Application of hydraulic or electrical energy through solenoid system shall open or close the valves for safe operation. After taking out stored production fluid from storage shells in shuttle tankers, the storage shells need to be reinstated at subsea level by removing the excess buoyant force through ballasting with ocean water. After reinstation process, the ballasted ocean water is to be pumped out which shall be done through de-ballasting pipeline. The electrical power requirements to various equipment’s are meet out from storage umbilical taking power through Control & Communication system.

In some embodiments, the plurality of shells is equipped with heating element through which the fluid ballasted while reinstation process, can be vaporized. The vapors of ballasted fluid are collected by Control & Communication System through flexible pressure tubing where the vapors can be regenerated to liquid form by condensation process again for reuse, if required. Refrigerants are most suitable fluids for the purpose of vaporization which ease the de-ballasting process.

The mooring system includes high tensile strength fibrous ropes, metallic chains, metallic poles and joint couplers. Fibrous ropes like dyneema fiber ropes can be used as mooring and guiding ropes due to its low specific gravity. The mooring ropes are anchored with foundation blocks at one end and with metallic chains through joint couplers at the other end. The guiding ropes are fixed with foundation system at bottom end and fixed with control & communication system rope winches at the other end. The bottom end of fibrous guiding rope is encased by rigid metallic pole of field of designed length. The diameter of metallic pole at the upper end is gradually reduced to form a cone shaped encasement around fibrous rope within designed length so as to guide the storage shell via monolithically casted grooves in it, in correct orientation on resting cage. A small proportion of mooring ropes in the topmost portion is metallic chain to facilitate the vertical motion of control & communication system via mooring winches fixed with it.

The control & communication system includes a buoy, mooring winch system, communication system, electrical batteries, guiding rope winches, emergency control equipment, main & storage umbilicals and umbilical winch. The buoy houses all the necessary equipments required to control the field, establishment of communication with onshore facilities and to provide sufficient buoyancy. Mooring winches are fixed with the buoy through which buoy can be move vertically by pulling in or out the mooring metallic chains. The communication system includes data interpretation system, signal transmission antenna inside small buoy, communication umbilical and rope winches. The data interpretation system controls all the hydromechanical and electromechanical system involved and is operated through onshore control facilities via satellite communication with the transmission antenna in the small buoy connected with data interpretation system via communication umbilical. The small buoy is fixed with main buoy via fibrous ropes through rope winches. The electrical batteries provide necessary power to all the equipments so as to perform their intended function. All the guiding ropes are attached with the buoy via rope winches. To access a particular storage shell, the guiding ropes of the concerned storage shell are taken off from the buoy rope winch and attached with shuttle tanker's heave compensator template and the storage umbilical remain attached with umbilical winch of buoy. The storage resting cage lock of storage system is opened and storage shell starts lifting up due to buoyant force. The storage umbilical is rolled around umbilical winch of buoy through winch rotation and similar process with opposite umbilical winch rotation is adopted while storage reinstation process. Emergency shells are fixed with the buoy for the condition when storage shell cannot be pulled up due to any equipment failure. The emergency shell provides necessary support to storage shells by unlocking it from storage resting cage, provide additional buoyant force etc.

In the context of the specification, the term “production fluid” refers to any fluid that comes out either from fully developed subsea well or from subsea well under development phase. The presence or absence of solid cuttings in the production fluid indicate the condition of subsea well i.e., under development process or fully developed. In the context of the specification, the term “umbilical” refers to the connections used offshore between the subsea equipment and platforms or floating units and enabling the control remotely. Umbilicals provide control, power, communications and chemical services between a subsea production arrangement and a remote floating facility.

In the context of the specification, the term “mooring system” refers to a system or an interface exist between the subsea production and floating unit. The mooring system includes a mooring line, anchor and connectors, and is used for station keeping of a ship or floating unit in all water depths.

In the context of the specification, the term “solid cutting” refers to the fragments of rock which are derived during the process of the well drilling.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

So that the manner in which the features of the present invention can be better understood, certain drawings are appended hereto. It is to be noted, however, that the drawings illustrate only selected embodiments of the invention and are therefore not to be considered limiting of scope, for the invention may admit other equally effective embodiments and applications.

These and other features, benefits, and advantages of the present invention will become apparent by reference to the following text figure, with like reference numbers referring to like structures across the views, wherein:

Fig. 1 illustrates a complete process flow of the present invention at a glance in a sequential manner;

Fig. 2 illustrates a system installation process flow in a sequential manner;

Fig. 3 illustrates a foundation installation process flow in a sequential manner;

Fig. 4 illustrates a production process of the present invention in a sequential manner; Fig. 5 illustrates the system dismantling process flow after completion of design period of a subsea plant in a sequential manner;

Fig. 6 illustrates the foundation dismantling process flow after completion of design period of the subsea plant in a sequential manner;

Fig. 7 illustrates a front view of assembly while transportation of field, in accordance with an embodiment of the present invention;

Fig. 8 illustrate a top view of assembly while transportation of field, in accordance with an embodiment of the present invention;

Fig. 9 illustrates a front view of field at an instant during sinking due to mud ballasting, in accordance with an embodiment of the present invention;

Fig. 10 illustrate a front view of field when mud ballasting process has completed, in accordance with an embodiment of the present invention;

Fig. 11 illustrates a front view of an instance after installation of control & communication system, in accordance with an embodiment of the present invention;

Fig. 12 & 13 illustrates a front view of field at an instance while transportation of a foundation block and during sinking due to mud ballasting, in accordance with an embodiment of the present invention;

Fig. 14 illustrates a front view of developed field at an instance before installation of metallic storage shells, in accordance with an embodiment of the present invention;

Fig. 15 & 16 illustrates a top view of developed field at an instance before installation of metallic storage shells, in accordance with an embodiment of the present invention; Fig. 17 illustrates a front view of developed field at an instance before starting of production, in accordance with an embodiment of the present invention;

Fig. 18 illustrates a front view of field at an instance during production process, in accordance with an embodiment of the present invention;

Fig. 19 illustrates a front view of field at an instance during accession of storage process, in accordance with an embodiment of the present invention;

Fig. 20 illustrates a front view of field at an instance during transportation of subsea storage from ocean bed to ocean surface by the storage shell, in accordance with an embodiment of the present invention;

Fig. 21 illustrates a front view of field at an instance after completion of storage offloading process and before start of storage shell reinstation process, in accordance with an embodiment of the present invention; and

Fig. 22 illustrates a front view of field at an instance after storage shell reinstation process, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Fig. 1 illustrates a complete process flow of the present invention at a glance in a sequential manner. The process flow 100 starts with a development process 102 of the subsea plant. The subsea plant is sub-divided into two components viz. “system" which refer to components of the subsea plant involving in the function of subsea production fluid storage & its transportation to ocean surface either directly or to support the other subsea plant components performing said function in direct manner like field 150, storage shells 40 etc. (illustrated in fig. 17) and “foundation" which refer to components of the subsea plant involving in the function of providing stability to the subsea plant. The development process 102 of the field is sub-divided into a system installation 104 and a foundation installation 106. A production process 108 starts after the successful completion of the development process 102, which shall remain continued till the end of design life of the field. After the end of design life, a dismantling process 110 shall be carried out in reverse manner as done previously for the development process 102. The dismantling process is further sub-divided into a system dismantling 112 & a foundation dismantling 114 processes.

Fig. 2 illustrates a system installation process 200 of the present invention in a sequential manner. The various components of system is shown in Fig. 7. The system assembly is so designed that it is sufficiently buoyant due to its buoyant components and it shall float on its own when placed in ocean water. The system installation process 200 of the present invention starts with a step 202 which includes the system transportation by pulling the system assembly by tug boats. After system transportation, in the next step 204, the system assemblies are to be lowered inside water upto ocean bed by partial mud filling with fluid denser than water so as to remove the excess buoyancy of system. The partial mud filling process is done by filling mud in the system but the invention is not limited to ballasting with mud only as any fluid denser than water is equally applicable to this invention. Upon removing the excess buoyancy by partial mud filling process, in the next step 206 the system is lowered inside water upto ocean bed, suitably oriented and placed. Once the system is placed on the ocean bed, complete ballasting is done with mud disclosed in step 208 to ensure system stability. In the next step 210, control & communication system 250 is installed and all the guide ropes 8 (illustrated in fig. 6) from the field 150 of the system are fixed with it and is disclosed in the final step 212.

Fig. 3 illustrates a foundation installation process 300 of the present invention in a sequential manner. The various components of foundation is shown in Fig. 12. The foundation assembly is so designed that it is sufficiently buoyant due to its buoyant components and it shall float on its own when placed in ocean water. The foundation installation process 300 starts with a step 302 which includes the transportation of the foundation block by pulling the foundation block assembly by tug boats. After foundation block transportation, in the next step 304 the foundation block assemblies are to be lowered inside water upto ocean bed by partial mud filling with fluid denser than water so as to remove the excess buoyancy of foundation block. The partial mud filling process is done by filling mud in the system but the invention is not limited to ballasting with mud only as any fluid denser than water is equally applicable to this invention. Upon removing the excess buoyancy by partial mud filling process disclosed in step 304, the foundation block is lowered inside water upto ocean bed, suitably oriented and placed in the step 306. Moving forward once the foundation blocks reaches the ocean bed, complete ballasting of the foundation block is done in step 308 to ensure foundation stability. Similar procedure is adopted for installation of all the other foundation blocks and all the mooring chains 35 fixed with mooring ropes 34 via joint couplers 36 (illustrated in fig. 14) and flexible pressure tubings 33 from the foundation blocks 350 are fixed with control & communication system 250 to complete the fixation process. The fixation process is done is step 310.

Fig. 4 illustrates a production process 400 of the present invention in a sequential manner. The production process 400 starts at step 402 where the production fluid is diversed to required production pipeline 14 through a subsea manifold 19 (illustrated in fig. 7). As a result, in the next step 404 the production fluid filling process starts in the storage shells 40 (shown in fig. 17) of concerned production pipeline 14. After completely filling the storage shells 40, the production fluid is diverted to other production pipeline 14 by the subsea manifold 19. The filled storage shells 40 are to be accessed for production fluid offloading and transportation to onshore facilities thereof. The entire subsea plant remain underwater except small buoy 26 of control & communication system 250 for establishment of satellite communication of subsea plant with onshore facilities. To access the filled storage shells 40, the mooring chains 35 fixed with control & communication system 250 (which is floating underwater) are unlocked, which results in upward movement of control & communication system 250 towards ocean surface due to excess buoyancy disclosed. The upward movement of the control & communication system 250 is disclosed in the step 406. Moving towards the next step 408, the guiding ropes 8 fixed with control & communication system 250 are taken off and attached with heave compensator. The filled shell mouth seal opened in the next step 410 and shell cage lock opening is done thereof at step 412. Moving forward to the next step 414, the storage shell 40 moves towards the ocean surface due to excess buoyancy of storage shell 40. Shell offloading process starts at step 416 for transfer of production fluid in offloading vessel. Upon completion of shell offloading process, the excess buoyancy of storage shell 40 is removed by shell ballasting disclosed in the step 418 with ocean water and the storage shell 40 moves to the ocean bed at step 420. Once the storage shell 40 reaches the ocean bed, shell cage again locked at step 422 and shell mouth seal is again closed at step 424 thereof. In the next step 426, the de-ballasting of the storage shell 40 for removing previously ballasted water is done through opening of de-ballasting pipeline 15 ball valves and injecting the de-ballasted ocean water inside ground through subsea injection well 39 connected with field 150 through ground injection pipeline 38 but the invention is not limited to above mentioned de-ballasting method as other de-ballasting techniques like de-ballasting through equipments fixed inside storage shell 40 or de-ballasting through pressure of production fluid filling in flexible storage membrane provided inside storage shell 40 by opening of small orifice gate for ocean water ejection, provided on the surface of storage shell 40 etc. are equally applicable. The control & communication system 250 again pulled back underwater for floatation at step 428. The processes 402 to 428 are repeated again and again till the end of design life of subsea plant for taking the production fluid.

Fig. 5 illustrates a system dismantling process 500 of the present invention after completion of design period of subsea plant in a sequential manner. The dismantling process 500 starts with a shell removal process from the field 150 disclosed in step 502 and then removal of control & communication system mentioned at step 504 by unlocking the mooring chains 35 fixed with control & communication system 250. The flexible pressure tubings 20 fixed with ballasting pipeline networks wherein 1 ^st flexible pressure tubing is fixed with lower ballasting pipeline network 18 and 2 ^nd flexible pressure tubing is fixed with upper ballasting pipeline network 17 are taken off for further de-ballasting process. In the next step 506, ocean water injection through 1 ^st flexible pressure tubing process starts from surface vessel pumps which shall force the initially ballasted mud in the system during the system installation process 200, towards upper ballasting pipeline network 17 and towards 2 ^nd flexible pressure tubing thereof. At step 508, mud recovery from 2 ^nd flexible pressure tubing takes place simultaneously with water injection via 1 ^st flexible pressure tubing process but the invention is not limited to recovering mud or any other fluid through a flexible pressure tubing as recovery process can also be done by filling the mud or any other fluid inside storage shells and accession of storage shells thereof through manipulation of shell buoyancy. Upon recovering all the mud initially ballasted, pressurized gas is injected via 1 ^st flexible pressure tubing at step 510 and taking out the previously ballasted ocean water via 2 ^nd flexible pressure tubing at step 512. Upon removal of all the previously ballasted ocean water, at the next step 514 the gas pressure is released which results in generation of positive buoyant force inside the field 150 (illustrated in fig. 7). Moving forward to the next step 516 where the system starts moving upward towards the ocean surface and finally transported to onshore facilities disclosed in the step 518.

Fig. 6 illustrates a foundation dismantling process 600 of the present invention after completion of design period of subsea plant in a sequential manner. The dismantling process 600 starts with the ocean water injection and removal by flexible pressure tubings 33. At step 602, the ocean water injection via 1 ^st flexible pressure tubing process starts from surface vessel pumps which shall force the initially ballasted mud in the foundation block during foundation installation 300, towards 2 ^nd flexible pressure tubing. Mud recovery for 2 ^nd flexible pressure tubing takes place at step 604 simultaneously with water injection via 1 ^st flexible pressure tubing process but the invention is not limited to recovering mud or any other fluid through a flexible pressure tubing as recovery process can also be done by filling the mud or any other fluid inside storage shells 40 and accession of storage shells 40 thereof through manipulation of shell buoyancy. Upon recovering all the mud initially ballasted, pressurized gas is injected via 1 ^st flexible pressure tubing at step 606 and taking out the previously ballasted ocean water via 2 ^nd flexible pressure tubing disclosed in step 608. Upon removal of all the previously ballasted ocean water, the gas pressure is released at step 610 which results in generation of positive buoyant force inside the foundation block 350. In the next step 612, the foundation block 350 starts moving upward towards the ocean surface 614 and finally transported to the onshore facilities disclosed in the step 616.

Fig. 7 illustrates a front view while transportation of field. During transportation of field, the towing rope 1 from tug boat 2 anchored with field hooks 3 provided at base plate 4 of cylindrical tank 5. The cylindrical tanks 5 at each storage collection point 6 in empty condition provides necessary buoyancy to the field 150 for floatation and connected with each other via tie beams 7. During transportation, all the guiding ropes 8 from rigid metallic poles 9 whose upper end diameter is gradually reduced to form a cone shaped encasement around guiding rope 8 within designed length, are attached with small boats 10 whose number are in accordance with the size of the field 150. The rigid metallic poles 9 are casted monolithically with lower half of storage resting cage lock 11, having anchor holes 12 adjacent to top of lower half of storage resting cage lock 11 so as to facilitate anchoring of upper half of cage lock's 41 key. The lower half of cage lock 11 is supported by intermediate metallic columns 13 casted monolithically with cylindrical tank 5 whose numbers are function of size of storage shell 40. The pipeline network viz. production pipeline network 14 and de-ballasting pipeline network 15 passing through each storage collection point 6 supported by metallic columns 16 at designed regular intervals which are fixed with tie beams 7, transfers the production fluid from production well via production pipeline network 14 and take out the de-ballasted ocean water via de-ballasting pipeline network 15 through storage collection point 6 provided with NRV and ball valves in both the pipeline networks below NRV for flow control. The cylindrical tank 5 are connected with ballasting pipeline network supported by intermediate metallic columns 16, at upper level 17 and lower level 18. During transportation, only towing ropes 1 are under tension and all the guiding ropes 8 are floating due to low specific gravity of component fibre.

Fig. 8 illustrates a top view of assembly while transportation of field 150. The tug boat 2 pulling the entire field 150 through towing ropes 1 anchored with the field hooks 3 at cylindrical tank base plate 4, also carry the flexible pressure tubings 20 from upper level 17 and lower level 18 ballasting pipeline network. The subsea manifold 19 is connected through production well templates 21 where production wells to be developed after installation of field 150 at ocean bed. All the subsea equipments except storage shells 40 are powered through subsea umbilical termination 22 unit via branch umbilicals 49. The subsea umbilical termination unit 22 is powered through main umbilical from control and communication system 250.

Fig. 9 illustrates a front view of field 150 at an instant during sinking due to ballasting of mud or any fluid denser than ocean water. Upon transportation of field 150 to offshore site location, mud of required density or any suitable fluid denser than ocean water is ballasted in cylindrical tanks 5 via flexible pressure tubings 20. As a result, the net upward force acting on the field 150 reduces. Mud ballasting process continues till the field 150 starts sink and net weight is so manipulated that onboard facilities easily handle field 150 weight during installation. Field 150 is lowered to ocean bed and placed according to required orientation. Mud ballasting process again starts after field 150 placement and all the cylindrical tanks 5 filled completely with mud solution.

Fig. 10 illustrates a front view of field 150 when mud ballasting process has completed. Mud density is so manipulated that it will counterbalance the upward buoyant force of empty storage shell 40 to maintain field 150 stability. The field 150 has been installed successfully after this stage.

Fig. 11 illustrates a front view of an instance after installation of control & communication system 250. Control & communication system 250 comprises of a large buoy 23 having enough buoyancy to support the dead weight of various equipments attached with it. All the guiding ropes 8 from the field’s metallic poles 9 are fixed with rope winches 24 and flexible pressure tubing 20 with tubing hangers 25 of control & communication system 250. The communication is established with onshore facilities via small buoy 26 fixed with large buoy 23 through buoy mooring ropes 27 rolled around rope winch 28. The top portion of large buoy 23 contains all the necessary equipments of communication system and electric power batteries. Emergency shells 29 are fixed with large buoy 23 having storage lock cage opening key 30, anchoring grooves 31 through which emergency shell 29 can be anchored with storage shell 40 via extrusions 42 provided. The power requirement of emergency shells 29 is meet out through surface vessels. The de-ballasting of ocean water from emergency shell 29 at subsea level is done through suitable de-ballasting equipment in practice.

Fig. 12 & 13 illustrates a front perspective view of field at an instance while transportation of a foundation block 350 and during sinking due to ballasting of mud or any fluid denser than ocean water. The foundation block 350 having large cylindrical tank 32 is transported and ballasted with mud, the same way as the complete field 150 system done before. Upon successful placement & mud ballasting process, both the flexible pressure tubings 33 are fixed with control & communication system 250 tubing hangers 25. On repeating the process for all the foundation blocks 350, the field 150 is ready for well development and thereafter for production process as shown in Fig. 14.

Fig. 14 illustrates a front view of developed field 150 at an instance before installation of metallic storage shells 40. The mooring ropes 34 attached with mooring chains 35 in the top within required portion of total mooring length via joint couplers 36, are fixed with mooring winches 37 of control & communication system 250. The rotation of mooring winches 37 leads to shortening or lengthening of mooring chain 35 which leads to downward or upward motion of control & communication buoy 23. To access the assemblies of control & communication system 250 at ocean surface, lengthening of mooring chain 35 is done and to protect the control & communication system 250 from surface wave/current forces continuously or against bad environmental conditions, shortening of mooring chain 35 is done which leads to floatation of buoy 23 at required underwater depths.

Fig. 15 & 16 illustrates a top view of developed field 150 at an instance before installation of storage shells 40. A de-ballasted water ground injection pipeline 38 radiating from subsea manifold 19 collects the de-ballasted water from each collection point 6 & inject it to subsea water injection well 39 via booster pump provided in subsea manifold assembly 19. Fig. 17 illustrates a front view of developed field 150 at an instance before starting of production. The field 150 is completely developed after installation of metallic storage shells 40 equipped with upper half of storage resting cage 41 locked through insertion of upper half s 41 anchor key in anchor holes 12 of metallic pole 9. The extrusions provided at the top of storage shell 42 facilitates the fixation of storage shell with anchor grooves 31 of emergency shell 29 in emergency condition and cage lock can be opened through rotation of upper half 41 via rotation of apex assembly 43 through storage cage lock opening key 30. The sealing/opening & closing of NRV/opening & closing of ball valves of production 14/de-ballasting 15 pipeline network, at collection point 6 is done through shell mouthpiece assembly 44 controlled through hydraulic or solenoid system. The power requirement for all the storage shell equipments is meet out through storage umbilical 45 taking power from control & communication system 250 and fixed with it at umbilical winch 46.

Fig. 18 illustrates a front view of field 150 at an instance during production process. The level sensors provided at inner lining of storage shell 40 transmits the production fluid level information to control & communication system 250 through storage umbilical 45 and finally to onshore control facilities via small buoy's 26 satellite communication. After completion of production process in the concerned pipeline network, the ball valve of production pipeline 14 and NRV of collection point 6 are closed. The fluid produced from wells is kept stored upto necessary level in storage shell 40 till stored production fluid offloading process.

Fig. 19 illustrates a front view of field 150 at an instance during accession of storage process. Before the accession process of stored production fluid, the lengthening of mooring chain 35 process by winch rotation 37 of buoy 23 starts so that the control & communication system 250 can move towards the ocean surface. The guiding ropes 8 of storage shell 40 fixed at rope winches 24 whose storage is to be offloaded, are fixed with heave compensator template 47 over offloading vessel 48 and tensioned upto design requirements. The storage umbilical 45 remains fixed with control & communication system umbilical winch 46. The upper half of storage resting cage lock 41 is opened which leads to lifting of storage shell due buoyant force as shown in Fig. 20. The magnitude of force depends upon the difference of bulk density of production fluid inside and ocean water outside the storage shell 40, the volume of storage shell 40 & production fluid inside and selfweight of storage shell 40. As the storage shell 40 lifts upwards, the storage umbilical 45 keeps rolling over umbilical winch 46 of control & communication system 250.

Fig. 21 illustrates a front view of field 150 at an instance after completion of storage offloading process and before start of buoyant storage shell 40 reinstation process. Storage shell 40 upon reaching to ocean surface, is offloaded via fluid offloading tube 50. The storage shell 40 after offloading process needs to be cleaned through chemical wash to avoid any underground water pollution due to inner lining contact with stored production fluid and then to be reinstated at subsea field 150, but to do so the excess buoyancy of storage shell 40 is to be removed so that it can sink due to its self-weight. Ballasting process through ocean water injection inside storage shell 40 starts to remove excess buoyancy. The level of ballasted water is monitored simultaneously, and process need to be stopped on reaching a specified level which is a function of offloading vessel’s 48 equipment lifting capacity. After ballasting process, the storage shell 40 starts sink due to its selfweight and guided upto lower half of storage resting cage 11 after which the cage is locked via rotation of upper half portion 41 of cage. After reinstation process, the guiding ropes 8 are again fixed with rope winches 24 of control & communication system 250. The rotation of mooring winches 37 of buoy 23 after shell 40 reinstation process leads to shortening of mooring chain 35 length and subsequent sinking of buoy 23 underwater upto required depths as shown in Fig. 22. The ball valves of production 14 & de-ballasting 15 pipeline network and NRV of collection point 6 are opened through shell mouthpiece assembly 44, so that storage shell 40 can be de-ballasted through de-ballasting pipeline network 15. The booster pump at subsea manifold 19 injects the de-ballasted water to underground strata via injection well 39. Finally, upon closing of ball valve of de-ballasting pipeline network 15 make the storage shell 40 ready for storage of production fluid that may contain solid cuttings. After the period of design life, the field needs to be dismantled. During field dismantling, ocean water is circulated through flexible pressure tubing 20 fixed with lower level 18 ballasting pipeline network. The previously ballasted mud or any fluid denser than ocean water in cylinder tanks 5 is forced to move out through upper level 17 ballasting pipeline network. Pressurized nitrogen gas is injected through flexible pressure tubing 20 fixed with lower level 18 ballasting pipeline network after forcing out all the mud, but the invention is not limited to only nitrogen gas as any other suitable gas is of same utility. Due to gas pressure, the previously ballasted ocean water is forced to move out through upper level 17 ballasting pipeline network. Finally, upon releasing the gas pressure through opening of valves in flexible pressure tubing 20, the field 150 is again made buoyant and lifted to ocean surface for transportation to onshore site.