Enhanced riser-based gas-lift apparatus

Abstract

An apparatus may include a production riser (1), an eductor (2), a motive fluid line (3), a suction line (4), and a mixed fluid line (5). The production riser may extend into a wellbore and be configured to convey production fluid from the wellbore to a wellhead (7). The eductor (2) may be configured to mix a slip stream (9) of the production fluid (6) with high-pressure motive fluid (12), providing a mixed fluid (9). The motive fluid line may extend into the wellbore from a compressor to the eductor and be configured to provide the high-pressure motive fluid to the eductor. The suction line may be configured to provide the slip stream from the production riser to the eductor. The mixed fluid line may be configured to convey the mixed fluid from the eductor to the production riser. A method and system may employ such an apparatus.

1 . An apparatus comprising:
 a production riser extending into a wellbore and configured to convey production fluid from the wellbore to a wellhead;   an eductor configured to mix a slip stream of the production fluid with high-pressure motive fluid, providing a mixed fluid;   a motive fluid line extending into the wellbore from a compressor to the eductor and configured to provide the high-pressure motive fluid to the eductor;   a suction line configured to provide the slip stream from the production riser to the eductor; and   a mixed fluid line configured to convey the mixed fluid from the eductor to the production riser.   
     
     
         2 . The apparatus of  claim 1 , further comprising a valve in the suction line. 
     
     
         3 . The apparatus of  claim 1 , further comprising a valve in the mixed fluid line. 
     
     
         4 . The apparatus of  claim 1 , wherein the mixed fluid line is configured to convey the mixed fluid from the eductor to the production riser at a point downstream of the suction line. 
     
     
         5 . The apparatus of  claim 1 , wherein the suction line and the mixed fluid line are each downstream of the wellhead. 
     
     
         6 . The apparatus of  claim 1 , wherein the compressor is outside the wellbore. 
     
     
         7 . The apparatus of  claim 1 , wherein the high-pressure motive fluid is provided, at least in part, from a different riser tied in to motive fluid line subsea. 
     
     
         8 . The apparatus of  claim 7 , wherein the motive fluid is a multiphase liquid and gas combination with a gas to oil ratio substantially higher than the gas to oil ratio of the production fluid upstream of the motive fluid line; and
 wherein the pressure of the high-pressure motive fluid is at least twice the pressure of the production fluid upstream of the motive fluid.   
     
     
         9 . A method for reducing base pressure in a subsea riser, comprising:
 providing an eductor upstream of a wellhead, wherein the wellhead is upstream of the subsea riser;   supplying the eductor with high-pressure motive fluid;   supplying the eductor with production fluid;   with the eductor, mixing the high-pressure motive fluid and the production fluid to produce a mixed fluid; and   introducing the mixed fluid upstream of the wellhead.   
     
     
         10 . The method of  claim 9 , wherein providing the eductor comprises connecting the eductor to a production riser.