System and method for injecting gas into a hydrocarbon reservoir

Abstract

Gas is supplied from a host facility ( 2 ) to an underwater gas compressor (10) via a connecting pipeline ( 6 ) and the gas compressor is connected to a plurality of gas injection wells ( 7 ) for a hydrocarbon reservoir via well supply flowlines ( 8 ). The gas compressor ( 10 ) compresses the supplied gas to a higher pressure, and drives the gas into the reservoir via the flowlines ( 8 ) and gas injection wells ( 7 ) at a pressure at least as high as the pressure of the production fluid in the reservoir. This raises the overall pressure in the reservoir to drive production fluid there to the host facility (2). The compressed gas may alternatively be injected into production fluid in a production well to provide a gas lift effect.

1 . A system for injecting gas into a hydrocarbon reservoir, comprising: 
 a host facility ( 2 ) having gas supply means ( 3 , 4 );    an underwater gas compressor ( 10 ) remote from the host facility, and connected to the gas supply means by a pipeline ( 6 ); and    at least one well ( 7 ) connected to the underwater gas compressor ( 10 ), whereby the gas compressor is arranged to supply the gas received from the pipeline ( 6 ) to the or each well ( 7 ) and into the hydrocarbon reservoir to improve conveyance of production fluid at least towards the host facility ( 2 ).    
   
   
       2 . A system as claimed in  claim 1 , wherein at least one said well ( 7 ) is an injection well, the gas compressor ( 10 ) being arranged to drive gas into the hydrocarbon reservoir via the or each injection well ( 7 ) at a pressure at least as high as the pressure of the production fluid in the reservoir to raise the overall pressure in the reservoir.  
   
   
       3 . A system as claimed in  claim 1 , wherein at least one said well is a production well ( 25 ), the gas compressor ( 10 ) being connected to inject gas into production fluid in the or each production well.  
   
   
       4 . A system as claimed in  claim 1 , wherein the gas compressor ( 10 ) is connected to the at least one well ( 7 ) by at least one flowline ( 8 ) which is able to withstand conveyed gas of a higher pressure than the pipeline ( 6 ) between the host facility ( 2 ) and the gas compressor ( 10 ).  
   
   
       5 . A system as claimed in  claim 1 , wherein the underwater gas compressor comprises a high pressure gas compressor ( 10 ) and the host facility ( 2 ) has at least one lower pressure gas compressor ( 4 ) for driving gas to the high pressure gas compressor ( 10 ).  
   
   
       6 . A system as claimed in  claim 1 , wherein the underwater gas compressor ( 10 ) is located at an underwater facility ( 5 ).  
   
   
       7 . A system as claimed in  claim 6 , wherein the underwater facility ( 15 ) includes fluid separating means ( 19 ) for separating gas from the production fluid and recirculation means ( 22 ) for conveying gas from the fluid separating means ( 19 ) into the gas compressor ( 10 ).  
   
   
       8 . A system as claimed in  claim 6 , wherein the underwater facility ( 15 ) is on a seabed, and the system includes a production fluid pipeline ( 24 ) for conveying production fluid from the underwater facility ( 15 ) to the host facility ( 36 ), the production fluid pipeline ( 24 ) including a production riser ( 37 ) from the seabed to the host facility ( 36 ), and the host facility is connected to the production riser ( 37 ) at or close to the seabed by a separate riser ( 39 ).  
   
   
       9 . A system as claimed in  claim 6 , wherein the underwater facility ( 25 ) includes a retrievable module ( 27 ) which incorporates the gas compressor ( 10 ).  
   
   
       10 . A system as claimed in  claim 1  including a power and control umbilical ( 13 ) extending from the host facility ( 2 ) to the underwater gas compressor ( 10 ) for conveying power and control signals to the gas compressor.  
   
   
       11 . A system as claimed in  claim 10 , wherein the power and control umbilical ( 13 ) is arranged to convey power and control signals required for other underwater equipment.  
   
   
       12 . A method for injecting gas into a hydrocarbon reservoir, comprising the steps of: 
 supplying gas from a host facility ( 2 ) to an underwater gas compressor ( 10 ) via a connecting pipeline ( 6 );    compressing the gas received by the underwater gas compressor ( 10 ) to a higher pressure; and    injecting the compressed gas into at least one well ( 7 ) connected to the underwater gas compressor ( 10 ), and into the hydrocarbon reservoir to improve conveyance of production fluid at least towards the host facility ( 2 ).    
   
   
       13 . A method as claimed in  claim 12 , wherein the step of injecting gas includes injecting gas into at least one injection well ( 7 ), the gas being driven into the hydrocarbon reservoir via the or each injection well at a pressure at least as high as the pressure of the production fluid in the reservoir.  
   
   
       14 . A method as claimed in  claim 12 , wherein the step of injecting gas includes injecting gas into at least one production well ( 25 ), the gas being injected into production fluid in the or each production well ( 25 ).  
   
   
       15 . A method as claimed in  claim 12 , including separating gas from the production fluid at an underwater facility ( 15 ) including the underwater gas compressor ( 10 ).  
   
   
       16 . A method as claimed in  claim 15 , including conveying at least some of the separated gas into the gas compressor ( 10 ).  
   
   
       17 . A method as claimed in  claim 15 , including disposing of at least some of the gas separated from the production fluid into at least one cavity ( 43 ) below the surface of the ground underneath the water in which the gas compressor ( 10 ) is located.  
   
   
       18 . A method as claimed in any one of claims  12 , including the steps of receiving production fluid at the host facility ( 36 ) via a production riser ( 37 ) from a seabed, and injecting gas from the host facility ( 36 ) into the production riser ( 37 ) at or close to the seabed.  
   
   
       19 . A method for handling production fluid, comprising the steps of: 
 receiving production fluid in an underwater facility ( 15 ) from a hydrocarbon reservoir;    separating gas from the production fluid in the underwater facility ( 15 ); and    disposing of the gas into at least one cavity ( 43 ) below the surface of the ground underneath the water in which the underwater facility ( 15 ) is located.