Systems and methods for subsea gas storage installation and removal

Abstract

A method for deploying a gas storage vessel below the surface of the water comprises coupling an upper end of the gas storage vessel to a deployment apparatus positioned at the surface of the water. The gas storage vessel has a total dry weight and a lower end opposite the upper end. The gas storage vessel also includes a storage tank defining an inner region inside the tank and an exterior region outside the tank. In addition, the method comprises lowering the gas storage vessel below the surface of the water with the deployment apparatus. Further, the method comprises pumping a buoyancy control gas into the inner region of the tank. The buoyancy control gas in the inner region of the tank generates a buoyancy force acting on the gas storage vessel.

1 . A method for deploying a gas storage vessel below the surface of the water, comprising:
 (a) coupling an upper end of the gas storage vessel to a deployment apparatus positioned at the surface of the water, wherein the gas storage vessel has a total dry weight and a lower end opposite the upper end, and wherein the gas storage vessel includes a storage tank defining an inner region inside the tank and an exterior region outside the tank;   (b) lowering the gas storage vessel below the surface of the water with the deployment apparatus; and   (c) pumping a buoyancy control gas into the inner region of the tank during (b), wherein the buoyancy control gas in the inner region of the tank generates a buoyancy force acting on the gas storage vessel during (b).   
     
     
         2 . The method of  claim 1 , further comprising:
 (d) ensuring the dry weight of the gas storage vessel minus the buoyancy force is greater than zero and less than a maximum load capacity of the deployment apparatus during (b).   
     
     
         3 . The method of  claim 2 , wherein the deployment apparatus has a maximum load capacity, and wherein (d) further comprises ensuring the dry weight of the gas storage vessel minus the buoyancy force is less than the maximum load capacity of the deployment apparatus. 
     
     
         4 . The method of  claim 2 , wherein the subsea gas storage vessel further comprises:
 a first inlet adapted to flow a stored gas into the inner region;   a second inlet adapted to flow the buoyancy control gas into the inner region;   a port in fluid extending through the tank and in communication with the inner region and the outer region;   a first valve adapted to control the flow of the stored gas through the first inlet; and   a second valve adapted to control the flow of the buoyancy control gas through the second inlet.   
     
     
         5 . The method of  claim 4 , wherein the second valve is open during (c), and (c) further comprises pumping the buoyancy control gas from the surface of the water through the second valve and the second inlet into the inner region of the tank. 
     
     
         6 . The method of  claim 5 , wherein the subsea gas storage vessel further comprises a first outlet adapted to exhaust the buoyancy control gas from the inner region to the outer region and a third valve adapter to control the flow of the buoyancy control gas through the first outlet;
 wherein the third valve is closed during (c).   
     
     
         7 . The method of  claim 6 , wherein the first outlet is disposed at the upper end. 
     
     
         8 . The method of  claim 4 , wherein (c) further comprises allowing water to flow freely through the port between the inner region and the outer region during (b). 
     
     
         9 . The method of  claim 1 , wherein (a) further comprises coupling a pipestring to the upper end of the gas storage vessel, wherein the pipestring has a longitudinal axis and extends from the gas storage vessel to the deployment apparatus; and
 wherein (b) further comprises lowering the gas storage vessel with the pipestring.   
     
     
         10 . The method of  claim 9 , wherein the pipestring includes an in-line damping device. 
     
     
         11 . The method of  claim 9 , wherein (a) further comprises coupling a supply line to the second inlet, wherein the supply line extends from the deployment apparatus to the gas storage vessel, and wherein (c) further comprises pumping the buoyancy control gas from the surface down the supply line, through the second valve and the second inlet into the inner region of the tank. 
     
     
         12 . The method of  claim 11 , wherein (c) further comprises pumping water along with the buoyancy control gas down the supply line, through the second valve and the second inlet into the inner region during (b). 
     
     
         13 . The method of  claim 11 , further comprising resisting the rotation of the pipestring and the gas storage vessel about the longitudinal axis during (b). 
     
     
         14 . The method of  claim 9 , wherein the deployment apparatus includes a derrick that supports the pipestring and the gas storage vessel, and lowers the gas storage vessel subsea. 
     
     
         15 . The method of  claim 1 , wherein the deployment apparatus includes a crane that supports the gas storage vessel and lowers the gas storage vessel below the surface of the water. 
     
     
         16 . The method of  claim 6 , further comprising:
 (e) anchoring the gas storage vessel to the sea floor after (b).   
     
     
         17 . The method of  claim 16 , wherein (e) relying on gravity to anchor the gas storage vessel to the sea floor or utilizing piles to anchor the gas storage vessel to the sea floor. 
     
     
         18 . The method of  claim 16 , wherein (e) comprises:
 (e1) engaging the sea floor with the lower end of the gas storage vessel;   (e2) closing the second valve;   (e3) opening the third valve; and   (e4) exhausting the buoyancy control gas from the inner region of the tank to the outer region through the third valve and the first outlet.   
     
     
         19 . The method of  claim 18 , wherein (e) further comprises:
 (e5) allowing water to flow through the port into the inner region during (e4).   
     
     
         20 . The method of  claim 19 , wherein the gas storage vessel includes a mud skirt at the lower end, and a ballast chamber containing ballast between the tank and the mud skirt, and wherein (e) further comprises (e6) penetrating the sea floor with the mud skirt. 
     
     
         21 . The method of  claim 20 , wherein (e) further comprises (e7) increasing suction between the lower end of the gas storage vessel and the sea floor. 
     
     
         22 . The method of  claim 19 , further comprising (f) storing the gas in the gas storage tank. 
     
     
         23 . The method of  claim 22 , wherein (f) comprises:
 (f1) opening the first valve;   (f2) flowing the gas through the first valve and the first inlet into the gas storage tank.   
     
     
         24 . The method of  claim 23 , wherein the gas storage vessel further comprises a flexible gas storage bag disposed in the gas storage tank, wherein the gas storage bag has a gas inlet in fluid communication with the first inlet. 
     
     
         25 . The method of  claim 24 , wherein (f) further comprises:
 (f3) flowing the gas through the first valve, the first inlet, and the gas inlet into the flexible gas storage bag.   
     
     
         26 . The method of  claim 25 , wherein (f) further comprises:
 (f4) displacing water in the tank with the gas flowing into the flexible gas storage bag;   (f5) flowing water through the port from the inner region to the outer region.   
     
     
         27 . A method, comprising:
 (a) disposing a gas storage vessel on the sea floor, wherein the gas storage vessel has an upper end distal the sea floor and a lower end engaging the sea floor and includes a gas storage tank defining an inner region inside the tank and an exterior region outside the tank, and wherein the gas storage tank includes a first inlet in fluid communication with the inner region, a first valve that controls the flow of fluid through the first inlet, and a port in fluid communication with the inner region and the exterior region;   (b) pumping a buoyancy control gas through the first valve and first inlet into the inner region to generate a buoyancy force acting on the gas storage vessel;   (c) displacing water in the inner region with the buoyancy control gas;   (d) flowing water through the port from the inner region to the outer region; and   (e) moving the gas storage vessel from the sea floor toward the surface.   
     
     
         28 . The method of  claim 27  further comprising:
 (f) flowing the buoyancy control gas through the port from the inner region to the outer region during (e). 
 
     
     
         29 . The method of  claim 28 , wherein (e) further comprises:
 coupling the upper end of the gas storage vessel to a deployment apparatus positioned at the surface of the water; and   applying a vertical lifting force to the gas storage vessel with the deployment apparatus.   
     
     
         30 . The method of  claim 29 , further comprising:
 (f) ensuring the dry weight of the gas storage vessel minus the buoyancy force is greater than zero and less than a maximum load capacity of the deployment apparatus during (e).   
     
     
         31 . The method of  claim 28 , wherein the subsea gas storage vessel further comprises:
 a second inlet adapted to flow a stored gas into the inner region; and   a second valve adapted to control the flow of the stored gas through the first inlet;   a first outlet adapted to flow the buoyancy control gas from the inner region to the outer region, the first outlet being positioned at the upper end;   a third valve adapted to control the flow of the buoyancy control gas through the first outlet.   
     
     
         32 . The method of  claim 31 , further comprising:
 closing the second valve and the third valve before (b).   
     
     
         33 . The method of  claim 28 , further comprising:
 decreasing suction forces between the gas storage vessel and the sea floor.   
     
     
         34 . The method of  claim 33 , wherein decreasing suction forces comprises pumping water from the exterior region to the interface between the gas storage vessel and the sea floor. 
     
     
         35 . The method of  claim 28 , further comprising:
 (g) maintaining a volume of a stored gas in the inner region of the tank during (e), wherein the stored gas in the inner region generates a buoyancy force acting on the gas storage vessel.   
     
     
         36 . The method of  claim 35 , wherein (e) further comprises:
 coupling the upper end of the gas storage vessel to a deployment apparatus positioned at the surface of the water;   applying a vertical lifting force to the gas storage vessel with the deployment apparatus;   ensuring the dry weight of the gas storage vessel minus the buoyancy force generated by the buoyancy control gas and the buoyancy force generated by the stored gas is greater than zero and less than a maximum load capacity of the deployment apparatus during (e).   
     
     
         37 . A system for storing a gas subsea, comprising:
 a subsea gas storage vessel including:
 a gas storage tank defining an inner region inside the tank and an exterior region outside the tank, wherein the tank has an upper end and a lower end opposite the upper end; 
 wherein the gas storage tank includes a gas inlet adapted to flow the gas into the inner region, an air inlet adapted to flow air into the inner region, a port in fluid communication with the inner region and the outer region; 
 a valve adapted to control the flow of gas through the gas inlet; and 
 a valve adapted to control the flow of air through the air inlet. 
   
     
     
         38 . The system of  claim 37 , wherein the subsea gas storage vessel further comprises:
 an air outlet adapted to exhaust air from the inner region to the outer region, wherein the air outlet is positioned at the upper end of the tank; and   a valve adapted to control the flow of air through the air outlet.   
     
     
         39 . The system of  claim 37 , wherein the subsea gas storage vessel further comprises:
 a ballast chamber coupled to the lower end and ballast disposed in the ballast chamber; and   a mud skirt extending from the ballast chamber.   
     
     
         40 . The system of  claim 39 , wherein the subsea gas storage vessel further comprises:
 a suction control apparatus coupled to the tank and adapted to control suction forces in the within the mud skirt.   
     
     
         41 . The system of  claim 40 , wherein the subsea gas storage vessel further comprises:
 a flexible gas storage bag disposed in the inner region of the tank, wherein the flexible gas storage bag is adapted to store the gas and includes a gas port in fluid communication with the gas inlet; and   wherein the flexible gas storage bag has a collapsed position when the bag is empty and an expanded position when the bag contains the gas.   
     
     
         42 . The system of  claim 41 , wherein the flexible storage bag has a first end proximal the upper end of the tank and a second end opposite the first end, wherein the gas port is disposed at the first end, and wherein the first end of the bag is oversized relative to the second end of the bag. 
     
     
         43 . The system  claim 41 , wherein the bag is positioned between the port and the upper end. 
     
     
         44 . The system of  claim 37 , further comprising:
 a deployment apparatus at the surface of the water and adapted for deploying the gas storage vessel subsea;   a pipestring extending from the deployment apparatus to the gas storage vessel, wherein the pipe string has an upper end positioned at the deployment apparatus and a lower end coupled to the subsea gas storage vessel.   
     
     
         45 . The system of  claim 44 , wherein the pipestring includes an inline damping device. 
     
     
         46 . The system of  claim 44 , wherein the deployment apparatus includes a derrick that supports the pipestring and the gas storage vessel. 
     
     
         47 . The system of  claim 37 , wherein the gas storage vessel has a central axis and a total dry weight;
 wherein the inner region comprises a first section extending axially from the upper end to the port, the first section having a total volume;   wherein the total volume times the density of water is less than the dry weight.