Subsea fluid processing system with intermediate re-circulation

Abstract

A fluid processing system is provided containing a pump and a fluid reservoir. The pump includes a casing, one or more pump stages, a pump inlet, and a pump outlet. The casing includes one or more slots, with at least one slot configured to extract at least a portion of a multiphase fluid flowing within the pump. The fluid reservoir encompasses at least a portion of the casing and is configured to receive and separate the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase. The fluid reservoir includes a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit. The discharge device regulates re-circulation of at least a portion of the extracted liquid phase to the pump via the pump inlet for reducing a gas volume fraction of the multiphase fluid being fed to the pump.

1 . A fluid processing system comprising:
 a pump including a casing, one or more pump stages, a pump inlet, and a pump outlet, the casing defining one or more slots, wherein at least one of the slots is configured to extract at least a portion of a multiphase fluid flowing within the pump, wherein each pump stage comprises a diffuser and an impeller; and   a fluid reservoir encompassing at least a portion of the casing and configured to receive and separate the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase,   wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet, and a discharge device coupled to the re-circulation conduit and configured to regulate re-circulation of at least a portion of the extracted liquid phase to the pump via the pump inlet so as to reduce a gas volume fraction (GVF) of the multiphase fluid being fed to the pump.   
     
     
         2 . The system according to  claim 1 , wherein the fluid reservoir further comprises a re-injection conduit coupled to the one or more pump stages upstream relative to the slots and configured to regulate re-injection of the extracted gaseous phase into the pump. 
     
     
         3 . The system according to  claim 1 , wherein the pump stages are arranged in a serial configuration. 
     
     
         4 . The system according to  claim 1 , wherein the pump stages are arranged in a parallel configuration. 
     
     
         5 . The system according to  claim 1 , wherein the one or more slots are located at about 20 percent to about 80 percent of a length of the diffuser. 
     
     
         6 . The system according to  claim 1 , wherein the one or more slots comprises at least one of a continuous slot, a discrete slot, a non-uniform slot. 
     
     
         7 . The system according to  claim 6 , wherein the one or more slots are positioned along at least one of a mid-chord length of the diffuser, a leading edge of the diffuser, and a trailing edge of the diffuser. 
     
     
         8 . The system according to  claim 1 , wherein the discharge device comprises a plurality of concentric cylinders with each cylinder having one or more holes for allowing the extracted liquid phase to flow through the discharge device. 
     
     
         9 . The system according to  claim 8 , wherein each cylinder comprises a side wall inclined at a pre-determined angle relative to the pump inlet, to regulate at least one a pressure and a quantity of extracted liquid phase being fed to the pump. 
     
     
         10 . The system according to  claim 1 , wherein the discharge device comprises a valve disposed in a pipe coupled between the re-circulation conduit and the pump inlet, for regulating a flow of the extracted liquid phase into the pump. 
     
     
         11 . The system according to  claim 1 , wherein the discharge device comprises a valve disposed in a pipe and coupled to an actuator disposed in a conduit, wherein the pipe is coupled to the re-circulation conduit and the pump inlet, and the conduit is coupled to the pipe and the fluid outlet, wherein the valve is configured to regulate a flow of the extracted liquid phase into the pump based on a pressure difference across the pump. 
     
     
         12 . The system according to  claim 1 , wherein the discharge device comprises a cylinder including one or more holes for allowing the extracted liquid phase to flow into the pump inlet. 
     
     
         13 . The system according to  claim 1 , wherein the discharge device comprises at least one of an active device and a passive device and configured to regulate a flow of the extracted liquid phase into the pump. 
     
     
         14 . A method comprising:
 introducing a multiphase fluid into a pump configured to increase pressure of the multiphase fluid, wherein the pump comprises a casing, one or more pump stages, a pump inlet, and a pump outlet, wherein each pump stage comprises a diffuser and an impeller;   extracting at least a portion of the multiphase fluid flowing within the pump into a fluid reservoir encompassing at least a portion of the casing via one or more slots defined in the casing, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit;   separating the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase;   re-circulating at least a portion of the extracted liquid phase through the re-circulation conduit into the pump via the pump inlet by regulating a flow of the extracted liquid phase via the discharge device; and   mixing the extracted liquid phase with the multiphase fluid at the pump inlet so as to reduce the gas volume fraction (GVF) of the multiphase fluid being fed to the pump.   
     
     
         15 . The method of  claim 14 , further comprising re-injecting the extracted gaseous phase into the one or more pump stages upstream relative to the slots via the re-injection conduit coupled to the fluid reservoir. 
     
     
         16 . The method of  claim 14 , wherein the regulating comprises controlling the discharge device having a plurality of concentric cylinders and one or more holes disposed on each cylinder, for allowing a flow of the extracted liquid phase into the pump. 
     
     
         17 . The method of  claim 14 , wherein the regulating comprises controlling the discharge device having a valve disposed in a pipe coupled between the re-circulation conduit and the pump inlet, for allowing a flow of the extracted liquid phase into the pump. 
     
     
         18 . The method of  claim 14 , wherein the regulating comprises controlling the discharge device having a valve coupled to an actuator, for allowing a flow of the extracted liquid phase into the pump based on a pressure difference across the pump, wherein the valve is disposed in a pipe and the actuator is disposed in a conduit, wherein the pipe is coupled to the re-circulation conduit and the pump inlet, and the conduit is coupled to the pipe and the fluid outlet. 
     
     
         19 . A method comprising:
 receiving a first production fluid in an inlet tank and mixing it with a primer liquid to produce thereby a second production fluid (multiphase fluid) having a reduced gas volume fraction (GVF) relative to the first production fluid;   introducing the multiphase fluid from the inlet tank into a pump configured to increase pressure of the multiphase fluid and produce thereby a compressed multiphase fluid, wherein the pump comprises a casing, one or more pump stages, a pump inlet, and a pump outlet, wherein each pump stage comprises a diffuser and an impeller;   extracting at least a portion of the multiphase fluid flowing within the pump into a fluid reservoir encompassing at least a portion of the casing via one or more slots defined in the casing, wherein the fluid reservoir comprises a re-circulation conduit disposed proximate to the pump inlet and a discharge device coupled to the re-circulation conduit;   separating the portion of the multiphase fluid into an extracted liquid phase and an extracted gaseous phase;   re-circulating at least a portion of the extracted liquid phase through the re-circulation conduit into the pump via the pump inlet by regulating a flow of the extracted liquid phase via the discharge device;   mixing the extracted liquid phase with the multiphase fluid at the pump inlet to further reduce the GVF of the multiphase fluid being fed to the pump; and   transporting the compressed multiphase fluid from the pump to a fluid storage facility via a fluid conduit.   
     
     
         20 . The method according to  claim 19 , further comprising re-injecting the extracted gaseous phase into the one or more pump stages upstream relative to the one or more slots via the re-injection conduit coupled to the fluid reservoir. 
     
     
         21 . The method according to  claim 19 , wherein the primer liquid comprises a liquid stream of the compressed multiphase fluid, which is delivered to the inlet tank via a re-circulation loop coupled to the fluid conduit, wherein the re-circulation loop comprises a control valve configured to regulate a flow of the liquid stream.