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A liquid storage, loading and offloading system includes a storage tank having a water ballast compartment for storing water and a liquid storage compartment for storing liquid. The water ballast compartment and the liquid storage compartment are coupled to each other to form a closed interconnected

A liquid storage, loading and offloading system includes a storage tank having a water ballast compartment for storing water and a liquid storage compartment for storing liquid. The water ballast compartment and the liquid storage compartment are coupled to each other to form a closed interconnected system with pressurized inert gas above water and liquid. The storage tank is configured symmetrically and the center of gravity and buoyancy of it move along a vertical Z axis. Besides, a pump module may also be included and have a pair of loading pumps and a pair of offloading pumps. The pair of loading pumps operates substantially at equal mass flow rate to displace water with liquid. The pair of offloading pumps also operates substantially at equal mass flow rate to displace liquid with water. Therefore an equal mass flow rate displacement system is formed to keep a constant draft.

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1. A liquid storage, loading and offloading system comprising: a storage tank comprising at least one water ballast compartment to store a water and at least one liquid storage compartment to store a liquid;a volume of inert gas disposed in upper ends of the water ballast compartment and the liquid

1. A liquid storage, loading and offloading system comprising: a storage tank comprising at least one water ballast compartment to store a water and at least one liquid storage compartment to store a liquid;a volume of inert gas disposed in upper ends of the water ballast compartment and the liquid storage compartment;wherein the upper ends of the water ballast compartment and the liquid storage compartment are fluidly coupled to each other to form a pressurized closed interconnected system; andwherein the structure of the storage tank is configured symmetrically. 2. The liquid storage, loading and offloading system according to claim 1 further comprising a valve connected to the water ballast compartment and to the liquid storage compartment; wherein the valve opens under a first condition and therefore the water ballast compartment and the liquid storage compartment become a pressurized-equalized closed interconnected system; and wherein the valve closes under a second condition and therefore the water ballast compartment and the liquid storage compartment become two separate systems not fluidly connected. 3. The liquid storage, loading and offloading system according to claim 1 further comprising a pump module coupled to the storage tank; wherein the pump module comprising at least one pair of loading pumps and at least one pair of offloading pumps; wherein the pair of loading pumps including a liquid loading pump to load the liquid into the liquid storage compartment and a water offloading pump to offload the water out of the water ballast compartment; and wherein the pair of offloading pumps including a water loading pump to load the water into the water ballast compartment and a liquid offloading pump to offload the liquid out of the liquid storage compartment. 4. The liquid storage, loading and offloading system according to claim 3 further comprising an equal mass flow rate displacement system to keep a constant operating weight such that the pair of loading pumps operate substantially at equal mass flow rate to displace the water with the liquid; and also such that the pair of offloading pumps operate substantially at equal mass flow rate to displace the liquid with the water. 5. The liquid storage, loading and offloading system according to claim 3 wherein the water offloading pump or the liquid offloading pump is replaced by a pressure energy of the inert gas in the water ballast compartment or the liquid storage compartment such that the pressure energy offloads the water or the liquid out. 6. The liquid storage, loading and offloading system according to claim 3 further comprising a converting valve coupled to the pump module for converting offloaded liquid to a different location. 7. The liquid storage, loading, and offloading system according to claim 1 further comprising a shuttle tank to receive an offloaded liquid from the storage tank or transmitting the liquid to the storage tank; and wherein the shuttle tank is coupled to the storage tank by a riser. 8. The liquid storage, loading and offloading system according to claim 1 further comprising a working station for providing power and control; and wherein the working station is coupled to the storage tank by a cable. 9. The liquid storage, loading and offloading system according to claim 1 further comprising a hydrocarbon production facility coupled to the storage tank by a pipeline. 10. The liquid storage, loading and offloading system according to claim 1 further comprising a fixing device attached to the storage tank for fixing the storage tank on a seabed and wherein an operating weight of the system is equal to or larger than a buoyancy of the system. 11. The liquid storage, loading and offloading system according to claim 1 further comprising a mooring positioning system attached to the storage tank for mooring the storage tank on a seabed in a floating condition. 12. The liquid storage, loading and offloading system according to claim 1 further comprising a solid ballast disposed adjacent to the storage tank to increase weights and damping and lower a center of gravity; and wherein a diameter of the solid ballast is equal to or larger than the diameter of the storage tank. 13. The liquid storage, loading and offloading system according to claim 1 wherein the liquid storage compartment is located inside of the water ballast compartment to form a tank-in-tank type of construction; wherein the liquid storage compartment and the water ballast compartment share a central axis; and wherein if a plurality of storage tanks exist, the plurality of storage tanks are arranged in symmetry and the plurality of storage tanks as a whole share the same central axis. 14. The liquid storage, loading and offloading system according to claim 1 wherein the liquid storage compartment is adjacent to the water ballast compartment, either horizontally or vertically, to form a not tank-in-tank type of the storage tank; wherein if a plurality of storage tanks exist, the plurality of storage tanks are arranged in symmetry and positioned apart from one another or positioned head-to-tail vertically or horizontally; and wherein a vertically positioned lower storage tank has a higher pressure of inert gas inside, than a vertically positioned higher storage tank. 15. The liquid storage, loading and offloading system according to claim 14 wherein if a plurality of water ballast compartments or liquid storage compartments exist, the plurality of water ballast compartments or liquid storage compartments are interconnected by a conduit respectively to become one water ballast compartment or one liquid storage compartment in substance. 16. The liquid storage, loading and offloading system according to claim 1 wherein the inert gas is nitrogen. 17. The liquid storage, loading and offloading system according to claim 1 wherein the storage tank is formed as a foundation of a bottom-supported platform. 18. The liquid storage, loading and offloading system according to claim 17 further comprising a topside facility to produce hydrocarbon, and a platform leg; wherein the platform leg is attached to the top of the storage tank; wherein the topside facility is connected to the platform leg; and wherein the hydrocarbon generated by the topside facility is stored directly in the storage tank. 19. The liquid storage, loading and offloading system according to claim 18 further comprises a moon pool for a riser or a conductor extending from an underground oil well to the topside facility. 20. The liquid storage, loading and offloading system according to claim 18 further comprising a fixing device to fix the bottom-supported platform on a seabed to form a bottom-supported and fixed platform; wherein a weight of the bottom-supported and fixed platform at a high water level is equal to or larger than a buoyancy of the bottom-supported and fixed platform, and therefore no heavy weight of the bottom-supported and fixed platform is required for stability; and wherein while the liquid inside the bottom-supported and fixed platform is drained, the weight of the bottom-supported and fixed platform is lighter than the buoyancy to help remove and relocate the platform. 21. The liquid storage, loading and offloading system according to claim 20 wherein the bottom-supported and fixed platform is sufficiently tall to pierce the water surface or near the water surface, and becomes a fixed artificial island. 22. The liquid storage, loading and offloading system according to claim 18 further comprising a mooring positioning system to moor the bottom-supported platform on the seabed in a floating condition to form a bottom-supported and floating platform; wherein a center of gravity of bottom-supported and floating platform is lower than a center of buoyancy of the bottom-supported and floating platform; and wherein a heaving period of the bottom-supported and floating platform is equal to or larger than 20 seconds to keep a constant operating weight. 23. The liquid storage, loading and offloading system according to claim 22 wherein the bottom-supported and floating platform is sufficiently tall to pierce the water surface or near the water surface, and becomes a floating artificial island. 24. The loading and offloading system according to claim 22 further comprising a protecting shield disposed above the storage tank to protect any impact from an outside environment and to increase weights and damping. 25. The liquid storage, loading, and offloading system according to claim 1 wherein the quantity of the inert gas is fixed. 26. A process of a loading and offloading system with equal mass flow rate displacement system comprising: transporting a stored liquid or water from a bottom of a liquid storage compartment or a water ballast compartment to an inlet of a liquid offloading pump or a water offloading pump by a pressure energy of an inert gas;offloading the stored liquid or water by the respective offloading pump or only by the pressure energy of the inert gas;supplying the inert gas to maintain pressure of the inert gas of the liquid storage compartment or the water ballast compartment;and wherein the supplied inert gas is from the water ballast compartment which is loaded with water at the same mass flow rate as the offloaded liquid, or from the liquid storage compartment which is loaded with liquid at the same mass flow rate as the offloaded water. 27. A liquid storage, loading and offloading system comprising: an artificial island comprising at least one water ballast compartment to store a water and at least one liquid storage compartment to store a liquid inside;a topside facility disposed above the artificial island to produce hydrocarbon;a volume of inert gas disposed in upper ends of the water ballast compartment and the liquid storage compartment; andwherein the upper ends of the water ballast compartment and the liquid storage compartment are fluidly coupled to each other to form a pressurized closed interconnected system; andwherein the hydrocarbon generated by the topside facility is stored directly in the artificial island. 28. The liquid storage, loading and offloading system according to claim 27 wherein the structure of the artificial island is configured symmetrically. 29. The liquid storage, loading and offloading system according to claim 27 further comprising a valve connected to the water ballast compartment and to the liquid storage compartment; wherein the valve opens under a first condition and therefore the water ballast compartment and the liquid storage compartment become a pressurized-equalized closed interconnected system; and wherein the valve closes under a second condition and therefore the water ballast compartment and the liquid storage compartment become two separate systems not fluidly connected. 30. The liquid storage, loading and offloading system according to claim 27 further comprising a pump module coupled to the artificial island; wherein the pump module comprising at least one pair of loading pumps and at least one pair of offloading pumps; wherein the pair of loading pumps including a liquid loading pmnp to load the liquid into the liquid storage compartment and a water offloading pump to offload the water out of the water ballast compartment; and wherein the pair of offloading pumps including a water loading pump to load the water into the water ballast compartment and a liquid offloading pump to offload the liquid out of the liquid storage compartment. 31. The liquid storage, loading and offloading system according to claim 30 further comprising an equal mass flow rate displacement system to keep a constant operating weight such that the pair of loading pumps operate substantially at equal mass flow rate to displace the water with the liquid; and also such that the pair of offloading pumps operate substantially at equal mass flow rate to displace the liquid with the water. 32. The liquid storage, loading and offloading system according to claim 27 further comprising a fixing device to fix the artificial island on a seabed to form a fixed artificial island; wherein a weight of the fixed artificial island at a high water level is equal to or larger than a buoyancy of the artificial fixed island; and wherein while the liquid inside the artificial fixed island is drained, the weight of the artificial island is lighter than the buoyancy to help remove and relocate the artificial island. 33. The liquid storage, loading and offloading system according to claim 27 further comprising a mooring positioning system to moor the artificial island on a seabed in a floating condition to form a floating artificial island. 34. The liquid storage, loading and offloading system according to claim 27 further comprising a solid ballast disposed adjacent to the artificial island to increase clamping and to improve a hydrodynamic performance; and wherein a diameter of the solid ballast is equal to or larger than a diameter of the storage tank. 35. The liquid storage, loading and offloading system according to claim 34 wherein the solid ballast is selected from the group consisting of a protruding skirt-shaped bottom solid ballast compartment, a protruding skirt-shaped lower solid ballast compartment, and a wheel-shaped solid ballast compartment. 36. A liquid storage, loading, and offloading system comprising: a storage tank comprising at least one water ballast compartment to store a water and at least one liquid storage compartment to store a liquid;a volume of inert gas;wherein the water ballast compartment and the liquid storage compartment are fluidly coupled to each other to form a closed interconnected system;wherein the structure of the storage tank is configured symmetrically;a pair of loading pumps for offloading the water out of the water ballast compartment and loading the liquid into the liquid storage compartment operating substantially at equal mass flow rate to displace the water with the liquid;a pair of offloading pumps for loading the water into the water ballast compartment and offloading the liquid out of the liquid storage compartment operating substantially at equal mass flow rate to displace the liquid with the water; andwherein an operating weight of the system is kept substantially constant.