Systems and methods for hydrate management

Abstract

An apparatus includes a first flow line, a second flow line and a seabed-disposed pump station. The first and second flow lines extend to a sea surface platform. The pump station to, in response to a shut down of a production flow in the first flow line, operate a pump of the station to transfer liquid from the first flow line to the second flow line to reduce a liquid column in the first flow line and push liquid in the second flow line to the sea surface platform for removal; and open a bypass valve for the pump to allow a liquid column in the second flow line to decrease to reduce a pressure in the second flow line during a period in which the pump station is shut down. The pump station may also be operated to communicate a pig through flow lines, and during a time interval in which the production is shut down, the pump station may be operated in a bypass mode to prevent hydrate formation in a subsea flow line.

1 . A method comprising:
 shutting down production from a subsea well, comprising reducing a pressure in a first flow line;   wherein reducing the pressure in the first flow line comprises:
 operating a seabed disposed pump to draw down liquid followed by gas to reduce a liquid level in a second flow line extending from a surface platform and push liquid in the first flow line to the surface platform; and 
 removing liquid from the first flow line at the surface platform. 
   
     
     
         2 . The method of  claim 1 , further comprising:
 operating the seabed disposed pump to communicate a production flow from the subsea well through the first flow line.   
     
     
         3 . The method of  claim 1 , wherein:
 removing the liquid from the first flow line comprises using a separator disposed on the surface platform; and   the first flow line extends to the separator.   
     
     
         4 . The method of  claim 3 , wherein reducing the pressure in the first flow line further comprises:
 operating a pump bypass valve to bypass the seabed disposed pump to decrease a liquid column height of the liquid in the first flow line.   
     
     
         5 . The method of  claim 3 , wherein reducing the pressure further comprises flaring gas present in the first flow line. 
     
     
         6 . The method of  claim 1 , wherein reducing the pressure in the first flow line further comprises:
 stopping the seabed disposed pump and allowing liquid in the first flow line to flow through a pump bypass valve and through a local recirculation path.   
     
     
         7 . The method of  claim 1 , wherein shutting down production comprises shutting down production flow through the first flow line and continuing a production flow through another flow line while production flow through the first flow line is shut down. 
     
     
         8 . An apparatus comprising:
 a first flow line to extend to a sea surface platform;   a second flow line to extend to the sea surface platform; and   a seabed-disposed pump station to, in response to a shut down of a production flow in the first flow line:
 operate a pump of the seabed-disposed pump station to flow a liquid followed by a gas in the first flow line and to transfer the liquid from the first flow line to the second flow line to reduce a liquid column in the first flow line and push liquid in the second flow line to the sea surface platform for removal; and 
 open a bypass valve for the pump to allow a liquid column in the second flow line to decrease to reduce a pressure in the second flow line. 
   
     
     
         9 . The apparatus of  claim 8 , further comprising:
 a wellhead valve to connect the first flow line to the second flow line to form a path to allow operation of the pump to transfer liquid from the first flow line to the second flow line.   
     
     
         10 . The apparatus of  claim 8 , wherein the seabed-disposed pump station closes the bypass valve, resumes operation of the pump and subsequently reopens the bypass valve to reduce the pressure in the second flow line during the period in which the seabed-disposed pump station is shut down. 
     
     
         11 . The apparatus of  claim 8 , wherein the pump operates to pump production fluid from a well, through the second flow line, and to the sea surface platform. 
     
     
         12 - 25 . (canceled) 
     
     
         26 . A system, comprising:
 a controller; and   a subsea pump communicatively coupled to the controller, wherein the subsea pump is configured to couple with first and second flow lines extending to a surface platform, the controller is configured to operate the subsea pump to drive a fluid flow from the surface platform to the subsea pump through the first flow line and from the subsea pump to the surface platform through the second flow line in response to a shutdown of a production flow, wherein the fluid flow in the first flow line comprises a liquid followed by a gas to reduce a first liquid level in the first flow line.   
     
     
         27 . The system of  claim 26 , wherein the controller is configured to operate the subsea pump to reduce the first liquid level in the first flow line to reduce pressure and hydrate formation in the first flow line. 
     
     
         28 . The system of  claim 27 , wherein the controller is configured to control removal of liquid in the second flow line at the surface platform to reduce a second liquid level, pressure, and hydrate formation in the second flow line. 
     
     
         29 . The system of  claim 28 , comprising a liquid gas separator coupled to the second flow line. 
     
     
         30 . The system of  claim 26 , comprising a bypass valve configured to bypass the subsea pump to reduce a second liquid level in the second flow line. 
     
     
         31 . The system of  claim 30 , wherein the subsea pump is coupled to a local recirculation path. 
     
     
         32 . The system of  claim 31 , wherein the local recirculation path comprises a loop between the subsea pump and a wellhead. 
     
     
         33 . The system of  claim 26 , comprising a valve disposed between the first and second flow lines. 
     
     
         34 . The system of  claim 33 , wherein the valve is disposed at a wellhead. 
     
     
         35 . The system of  claim 26 , comprising at least a portion of the first flow line and at least a portion of the second flow line. 
     
     
         36 . A method, comprising:
 identifying a shutdown condition of a production flow; and   controlling a subsea pump to drive a fluid flow from a surface platform to the subsea pump through a first flow line and from the subsea pump to the surface platform through a second flow line in response to the shutdown condition, wherein the fluid flow in the first flow line comprises a liquid followed by a gas to reduce a first liquid level in the first flow line.   
     
     
         37 . The method of  claim 36 , wherein controlling the subsea pump comprises reducing the first liquid level in the first flow line to reduce pressure and hydrate formation in the first flow line. 
     
     
         38 . The method of  claim 37 , comprising controlling removal of liquid in the second flow line at the surface platform to reduce a second liquid level, pressure, and hydrate formation in the second flow line. 
     
     
         39 . The method of  claim 36 , comprising controlling a bypass valve to bypass the subsea pump and provide fluid flow along a local recirculation path between the subsea pump and a wellhead.