Abstract:
A subsea storage tank for the storage of bulk fluids is adapted for being set on the sea floor, and is adapted for supplying to local subsea oil and gas production facilities a wide variety of production support fluids. The subsea storage tank includes an inner and outer shell, the shells being adapted so that a barrier fluid can be inserted into and between the shells. An interior barrier separates the interior stored fluid from sea water that is free to enter into the tank, on the opposite side of the barrier, to compensate to the varying volume of stored fluid. An identical tandem barrier is formed nearly identical to the first barrier, and is formed and positioned so that the two barriers act together, and so that the space between them can contain fluid as well, and acts like a bladder.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of provisional patent application Ser. No. 62/102,743, filed Jan. 13, 2015. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT 
     Not Applicable. 
     INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The invention relates to a tank for the storage of fluids and chemicals subsea. 
     (2) Description of Related Art 
     Tanks that are placed subsea must have certain features to ensure their survivability in the environment. They must contain the working fluids, be compensated to the outside environment and related hydrostatic pressure, and remain intact and in service for the length of their intended mission. 
     U.S. Pat. No. 7,424,917, which is incorporated herein by this reference, discloses a subsea pressure compensation system which includes a chamber with a piston therein acted on an exposed side by sea water, to provide operational hydraulic fluid for operating a subsea device, with a piston rod having an end in a separate chamber acted on by a fluid to compensate for a pressure differential between the pressure of the water on one piston side and the pressure of the operational hydraulic fluid on the other piston side. However, this reference does not teach, nor suggest, using any of the compensator system or system of pumps to act upon the compensator itself as a self-contained method to test or measure the integrity of the compensator itself, or of any of the barriers that separate the internal fluid from the surrounding outside fluid. 
     U.S. patent application No. 20080210434A1, which is incorporated herein by this reference, discloses a subsea and modular tanker-based hydrocarbon production system comprising a plurality of interlinked individual tank units which is wholly submersible. However, this reference does not teach, nor suggest, utilizing a pump to generate either a fluid pressure or vacuum to measure the integrity of the walls of the tank. 
     U.S. patent application No. 20130167962A1, which is incorporated herein by this reference, describes a pressure compensator for a subsea device that embodies the ability of the subsea tank to remain pressure compensated. However, this reference does not teach, nor suggest, using the fluid that is contained between the walls of the compensator to be used in a test protocol to assure the integrity of the wall, or barrier, of the compensator or vessel. 
     U.S. patent application No. 20150246770A1, which is incorporated herein by this reference, discloses a subsea storage tank, including a body having a storage space therein and formed of light weight concrete inner and outer sides of which are watertight coated or plated. However, this reference does not teach or suggest provisions that allow for the pressurization or vacuum of fluid between the tank inner and outer sides, nor could the fluid in this location be used to test the integrity of either wall of the storage tank or the integrity of the seals of the separation unit. 
     In light of the foregoing, a need remains for a modular subsea tanker hydrocarbon system, having a dual wall tank, and a barrier bladder, and utilizing a pump to generate either a fluid pressure or vacuum to measure the integrity of both the walls of the tank, and the barrier bladder, to sea water or working fluid. 
     BRIEF SUMMARY OF THE INVENTION 
     A subsea storage tank for the storage of bulk fluids, adapted for being set on the sea floor and adapted for supplying to local subsea oil and gas production facilities a wide variety of production support fluids. The subsea storage tank includes an inner and outer shell. The shells are adapted so that fluid can be inserted between the shells. The tank is split into two nearly identical halves, each half having a flange to bolt and assemble the halves into a complete tank. Into and between the flanged halves of the tank, a barrier that also is sealed like a bladder is placed to isolate and prevent comingling of a storage fluid in one half of the tank from the other half. An interior volume is dedicated to the storage of bulk fluids. An interior barrier separates the interior stored fluid from sea water that is free to enter into the opposite side of the barrier to compensate to the varying volume of stored fluid. An identical tandem barrier is formed nearly identical to the first barrier, and is formed and positioned so that the two barriers act together, and so that the space between them can contain fluid as well, and acts like a bladder. A light film of mineral oil or other fluid is between these two barriers so that they are free to slide against each other. The tank includes a pressure or vacuum pump and associated automatic valves so that the shell, and the barrier bladder, can be pressurized or vacuum drawn down to test the integrity of either the shell or the barrier bladder. This testing can be performed at any time, either locally or remotely, either on the surface above the water, or in service subsea, and whether or not the tank contains any amount of bulk fluid. The tank is adapted for lowering subsea either full or empty of bulk fluid, and is adapted for fitting to a temporary or permanent subsea structure, by hoses, pipes, or hydraulic couplings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The novel features, characteristic of the invention, are set forth in the appended claims. However, the invention itself, as well as a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description, when read in conjunction with the accompanying drawings in which the left-most significant digit in the reference numerals denotes the first figure in which the respective reference numerals appear. 
         FIG. 1A  is a cross-section view of a tank with schematic representations of the tank&#39;s dual shells, dual barrier bladder, fluid connections, sump pans, test pumps, valves, and associated instruments. 
         FIG. 1B  is a cross section of the dual barrier bladder showing the first barrier wall, second barrier wall, the porous mesh between the walls, and the fluid access port. 
         FIG. 1C  is a schematic diagram showing a separation flange of the tank, the dual barrier bladder, and a porous mesh that is between the two barriers of the bladder. 
         FIG. 2  is a schematic diagram showing equipment used to test the dual shells of the tank. 
         FIG. 3  is a schematic diagram showing equipment used to test the dual barrier bladder inside the tank. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1A , a storage tank  100  is full of bulk fluid  102  such that a dual barrier bladder  104  is pushed against an inner tank shell  103  and two sump pans  108 . This full position actuates a first large diameter piston  110 , applying force to a tank full limit switch  112 , which generates a signal to stop filling the tank  100 . When stop filling is indicated, a fill valve  114  closes. A second large diameter piston  116  and a tank empty limit switch  118  are located at the bottom of the tank  100  such that when the tank  100  is emptied, the dual barrier bladder  104  applies a force against the second large diameter piston  116 , which in kind, applies a force against the limit switch  118 , sending a control signal to shut a discharge valve  120 . During either fill or discharge operation, a sea water compensation valve  122  is open to allow the free flow of sea water into the interior of the tank  100  and to the opposite side of the dual barrier bladder  104 .  FIG. 1A  shows a cross section of the tank  100  independent of the overall potential size of the tank  100 . This configuration can be applied to tanks of relatively small volumes of several hundred gallons to tanks sized well over thousands of gallons. The defining quality of the geometry of the tank  100  is that the tank  100  is comprised of split halves, a first shell half  130 , which is flanged and bolted to a second shell half  132 , which creates a flange  134  to seal the edges of the dual barrier bladder  104 , which is fastened together with bolts  138 . Each shell half  130  and  132  is constructed as a dual wall shell, so that in each shell half  130  and  132  a fluid can be placed in a space  140  between the inner tank shell  103  and an outer tank shell  101 , and can be sealed and controlled. 
     The first shell half  130  and the second shell half  132  are tested by a tank shell test package  170 , through a tubing conduit connection drawing on the fluid in the space  140 . The shell test package  170  is shown in  FIG. 2 . This testing can be accomplished when the tank  100  is on the surface, or below sea water, and at any time. The dual barrier bladder  104  is tested by a dual barrier bladder test package  172 , shown in  FIG. 3 . This testing can be accomplished when the tank  100  is on the surface or below sea water, and at any time, and can be accomplished concurrently with testing either shell half  130  or  132 . 
     Filling operations of the tank require that the fill valve  114  be opened, so that bulk fluid can then be pumped into the tank  100 . The discharge valve  120  may be open or closed, and the tank  100  can be discharging or not discharging during the fill operation. The tank  100  can be filled before deployment subsea, and can be filled while deployed subsea during operation or when idle. 
     Measurement of the tank  100  levels for volumes of either the bulk fluid, or of compensating sea water, is performed by tracking and comparing the amount of either fluid as it enters or exits the tank  100 . A flow meter  156  for the sea water compensation measures the amount of sea water that enters and exits the tank  100 . A fill flow meter  162  measures the amount of bulk fluid that enters the tank  100 . A discharge flow meter  164  measures the amount of bulk fluid that is discharged from the tank  100 . A control method is established that compares the amount of fluid that passes each of these meters  156 ,  162 , and  164 . This amount is always compared so that it is understood to very exact amounts how much bulk fluid, or sea water, is in the tank  100 . If for any reason the tank  100  is completely emptied or completely filled, the tank empty limit switch  118  or the tank full limit switch  112  will signal the control system to stop discharge, stop fill, or close the discharge valve  120 , the fill valve  114 , or the sea water compensation valve  122 . 
     The fill valve  114 , the discharge valve  120 , and the safety valve  146  are necessary to ensure that the storage tank  100  cannot be compromised should a malfunction of a control system (not shown) occur. The safety valve  146  for the discharge fill piping  148  will open should the storage tank  100  become over-pressured. The compensation valve  122  is also a safety valve in that it is normally open, and the control system is required to shut it in any necessary operation. A pressure transducer  174  measures internal tank pressure, and differential pressure between the inside and outside of the storage tank  100 . When the pressure transducer  174  signals that an overpressure or under pressure condition is detected of a certain value, the fill valve  114  and the discharge valve  120  can be automatically closed. 
     On the top and bottom of the storage tank  100  are two access ports  176  and  178 . The access port  176  has a piston  110 , and the access port  178  has a piston  116 . The pistons  110  and  116  will translate when the dual barrier bladder  104  presses from the inside against the pistons  110  and  116 . The pressure by the dual barrier bladder  104  pushes the pistons  110  and  116  against limit switches  112  and  118 , thus signaling the position of the dual barrier bladder  104 . The limit switch  112  signals that the storage tank  100  is full of bulk fluid. When the limit switch  118  signals, then the storage tank  104  is empty of bulk fluid. Included in the access port  176  is a vent and drain valve  180 . The vent and drain valve  180  is used for releasing trapped air in the assembled storage tank  104 . The vent and drain valve  180  is also used for releasing trapped air in the first shell half  130  and in the second shell half  132 , or for draining fluid from either the first shell half  130  or from the second shell half  132 . When differential pressure is detected by the pressure transducer  174  of a certain value, the fill valve  114  and the discharge valve  120  can be automatically closed. 
     A fine sea water filter  182  and a coarse marine life excluder  184  are used together to keep debris and marine life from entering the tank. A vent valve  188  is located at the top of the tank  100  and the first shell half  130  to allow air to be vented when filling the space  140 . 
       FIG. 1B  shows a first barrier bladder wall  105 , a second barrier bladder wall  106 , and a porous mesh membrane  107 , which is located between the first barrier bladder wall  105  and the second barrier bladder wall  106 , which together form the dual barrier bladder  104 . Bonded between the walls  105 ,  106  is a tube access port  186  that allows fluid to enter from the dual barrier bladder test package  172  into a bladder inner space between the walls  105 ,  106  of the dual barrier bladder  104 . 
       FIG. 1C  shows a view of the flange  134  of the storage tank  100 , the dual barrier bladder  104 , and the porous mesh membrane  107 . The flange  134  is shown with a gap to illustrate the dual barrier bladder  104 , the first barrier bladder wall  105 , the second barrier bladder wall  106 , and the porous mesh membrane  107 , which is sealed by the flange  134 . The bolts  138  are shown elongated only to illustrate the dual barrier bladder  104  and the porous mesh membrane  107 . The porous mesh membrane  107  allows the free flow of lubricating oil or other fluid to flow and communicate throughout the entire inner space surfaces. 
       FIG. 2  shows the tank shell test package  170 , which includes a pump  210 , valves  212  and  216 , a pressure transducer  232 , a regulator valve  230 , and a fluid storage compensator  214 . The pump  210  can be configured to either pressurize or pull a vacuum on the first shell half  130  and the second shell half  132 . The pump operation is controlled by an operator either at the storage tank  100  or remotely. When the pump  210  is operated, the valve  212  opens and allows fluid to flow from or into the fluid storage compensator  214 . The fluid storage compensator  214  is sealed from the outside environment. The fluid storage compensator  214  can be filled or vented with the valve  216 . 
     When the pump  210  is used for a test, it is operated for a specific amount of time until a designated pressure or vacuum is reached. This test pressure or vacuum is regulated by a regulator valve  230 , that can be either locally adjusted or remotely adjusted, and remotely controlled. The test pressure or vacuum is measured by a pressure transducer  232 . Once desired pressure or vacuum is achieved, the valve  212  is closed, trapping the pressure or vacuum to be recorded and viewed for a defined amount of time. Upon completion of the test, both the valve  212 , and a valve  234 , are opened to allow fluid to flow from the fluid storage compensator  214  to equalize the fluid pressure. A valve  246  is used to fill the first shell half  130  and the second shell half  132  with fluid. 
       FIG. 3  shows the dual barrier bladder test package  172 , which includes a dual barrier bladder testing pump  310 , valves  312 ,  316 ,  330 , and  334 , a pressure differential transducer  332 , a regulator valve  330 , and a fluid storage compensator  314 . The pump  310  can be configured to either fill or pull a vacuum on the dual barrier bladder  104 , via the access port  186  bonded into the perimeter seal of the dual barrier bladder  104 . The access port  186  allows fluid to be placed between the walls of the dual barrier bladder  104 , and then removed from between the walls of the dual barrier bladder  104 . The pump  310  operation is controlled by an operator either at the storage tank  100  or remotely. When the pump  310  is operated, the valve  312  opens and allows fluid to flow from or into the fluid storage compensator  314 . The fluid storage compensator  314  is sealed from the outside environment. The fluid storage compensator can be filled or vented with the valve  316 . A valve  346  allows fluid to be added, drained, or vented from the dual barrier bladder  104 . The valve  346  is used to test and flush the pump  310 . 
     When the pump  310  is used for a test, it is operated for a specific amount of time until a designated vacuum is reached. This test vacuum is regulated by the valve  330 , that can be either locally adjusted or remotely adjusted, and remotely controlled. The test vacuum is measured by a pressure differential transducer  332 . Once desired vacuum is achieved, the valve  312  is closed, trapping the vacuum to be recorded and viewed for a derived amount of time. Upon completion of the test, both the valve  312 , and the valve  334 , are opened to allow fluid to flow from the fluid storage compensator  314  to equalize the fluid pressure. The dual bladder barrier  104  is configured in nearly two identical formed layers to the interior half of the storage tank  100  that are chemically resistant, impermeable coated fabric barriers.