Submerged oil storage, loading and offloading system

Abstract

An oil storage, loading and offloading system includes a submerged oil storage tank with multiple vertically placed flexible containers. The system directly connects to the topsides of an offshore oil production platform above water to assist oil loading and offloading operations. During loading, oil is pumped in and stored inside flexible containers, which are expanded to displace equivalent amount of water out of the oil storage tank; during offloading, oil is pumped out from flexible containers and the reduced volume of each contracted container is then filled in by the equivalent amount of water from the surroundings There is no physical contact between water and oil. The submerged tank on-bottom weight has a limited variation during the loading and offloading operations. This disclosed system can be utilized for fixed offshore platforms, especially for shallow water marginal field developments, and for deepwater floating platforms such as SPAR and semi-submersible (SEMI) structures.

What is claimed is: 
     
         1 . A deepwater floating platform equipped with submerged oil storage apparatus comprising:
 a floating body with at least one vertically placed floating structure to support a topsides above water surface for offshore oil production;   at least one submerged oil storage tank for storing oil and water together located below a plurality of hard tanks inside each floating structure, wherein the storage tank comprises a plurality of non-sealed vertical compartments, each vertical compartment housing one vertically placed flexible container for oil storage, with the remaining room of the compartment for water storage, without any physical contact between oil and water, each vertical compartment having a constant total storage volume and an equalized internal water pressure with surroundings while the volume for either oil or water storage varies with oil loading or offloading, each flexible container being fixed with the vertical compartment both at top and at bottom to maintain its vertical orientation throughout its service life;   an interconnected piping system to have multiple communication channels connected at one end with each of all flexible containers and at the other end with the topsides of the associated platform above the water surface, wherein at least one channel is used for oil 2-way flow during oil loading and offloading operations;   at least one fluid channel utilized for water one-way flow during oil offloading operation, with one end positioned outside the tank, equipped with a check valve, to allow one-way free flow-in from surrounding water outside of the tank and with the other end positioned inside the tank;   at least another fluid channel utilized for water one-way flow during oil loading operation with one end positioned inside the tank and the other end positioned inside a vessel at the topsides of the floating platform for water monitoring/processing before being discharged to the surrounding water; and   a fender system for ship docking.   
     
     
         2 . The deepwater floating platform equipped with submerged oil storage apparatus according to  claim 1 , wherein the interconnected piping system comprises—
 a) a hot liquid circulation system, 
 b) an oil loading and offloading system, 
 c) an air injection and release system, and 
 d) a system for placing sensors. 
 
     
     
         3 . The deepwater floating platform equipped with submerged oil storage apparatus according to  claim 1 , wherein the vertical compartment has a polygonal cross-section shape. 
     
     
         4 . The deepwater floating platform equipped with submerged oil storage apparatus according to  claim 1 , wherein the flexible container is a rubber bag composed of a plurality of layers:
 a) a top layer composed of a plurality of sub-layers with rubber material and a plurality of fiber nets bonded together through vulcanization,   b) a thermal insulation layer with thermal insulation material,   c) an air sealing layer composed of a thin rubber sheet or a sheet made of synthetic materials, and,   d) a chemical protection layer composed of a thin sheet with anti-chemical corrosion property, which could be glued to the inner surface of the air sealing layer.   
     
     
         5 . The deepwater floating platform equipped with submerged oil storage apparatus according to  claim 1 , wherein the floating body is a conventional floating SPAR platform, comprising:
 a single deep draft floating hull in a vertically oriented tubular shape, wherein a plurality of hard tanks and ballast tanks, with one center well for each tank, located at upper portion of the hull to provide buoyancy and stability for the floating body as well as a soft tank, and another center well at the bottom of the hull; and   at least one submerged oil storage tank to be added and located below the hard tanks and ballast tanks with a third center well to match with the center wells above, wherein a plurality of vertically placed steel compartments, each housing one flexible container for oil storage, to be placed between the tank inner surface and the third center well outer surface.   
     
     
         6 . The deepwater floating platform equipped with submerged oil storage apparatus according to  claim 1 , wherein the floating body is a floating truss SPAR platform, comprising:
 a floating upper hull in a vertically oriented tubular shape, wherein a plurality of hard tanks and ballast tanks to be located, with a first center well for each tank, to provide buoyancy and stability for the floating body;   a truss structure with multiple heave plates located between the upper hull and a soft tank, having a second center well at the bottom of the floating body; and   at least one submerged oil storage tank to be added and located below the hard tanks and ballast tanks with a third center well to match with the center wells above, wherein a plurality of vertically placed steel compartments, each housing one flexible container for oil storage, to be located between tank inner surface and the third center well outer surface.   
     
     
         7 . The deepwater floating platform equipped with oil storage apparatus according to  claim 1 , wherein the floating body is a semi-submersible (SEMI) platform and the vertically placed floating structure is a floating column of the SEMI platform, the SEMI platform comprising:
 a plurality of vertical floating columns connected between the topsides above and a plurality of submerged pontoons below, wherein a plurality of hard tanks are located at each floating column to provide buoyancy and stability for the semi-submersible (SEMI) platform; and   at least one submerged oil storage tank be located at bottom of each column with a passage way at its center, and a plurality of vertically placed steel compartments, each housing one flexible container for oil storage, located around the passage way.   
     
     
         8 . The deepwater floating platform equipped with oil storage apparatus according to  claim 7 , wherein the vertically placed steel compartments have an octagonal cross-section shape.