Method for Viscous Hydrocarbon Production Incorporating Steam and Solvent Cycling

Abstract

A method for producing hydrocarbons from a reservoir containing the hydrocarbon comprises a steam assisted gravity drainage (SAGD) incorporating cyclic steam, heavy (e.g. greater than C4) solvent and light (e.g. C2 to C4) solvent injection. The method involves a series of steps wherein the injection of the respective streams is varied. The method provides a significant improvement in hydrocarbon extraction efficiency as compared to a SAGD process alone and mitigates many of the drawbacks associated with typical SAGD operations.

1 . A method of producing hydrocarbons from a subterranean reservoir containing said hydrocarbons, the reservoir including at least one generally horizontal injection well and at least one generally horizontal production well, the production well being located vertically below the injection well and proximal thereto, the method comprising:
 a) injecting steam and, optionally, a heavy solvent into the reservoir through the at least one injection well, the heavy solvent comprising one or more hydrocarbons having a carbon chain length of C4 or greater;   b) reducing the steam injection rate, stopping the heavy solvent injection, and injecting a light solvent, the light solvent comprising one or more hydrocarbons having a carbon chain length less than the heavy solvent;   c) increasing the steam injection rate to above the rate of step (b), optionally restarting the heavy solvent injection, and continuing the light solvent injection;   d) increasing the steam injection rate to above the rate of step (c), stopping the heavy and light solvent injection; and,   e) reducing the steam injection rate and restarting the light solvent injection.   
     
     
         2 . The method of  claim 1 , further comprising a further step of:
 f) stopping injection of the steam and light solvent and scavenging residual solvents from the reservoir.   
     
     
         3 . The method of  claim 1 , wherein the heavy solvent is pentane or a hydrocarbon mixture having an average chain length of about C5 or greater and comprising at least ⅓ by volume of pentane and/or hexane. 
     
     
         4 . The method of  claim 1 , wherein the light solvent is propane or a hydrocarbon mixture having an average chain length of about C3 and comprising at least ½ by volume of propane. 
     
     
         5 . The method of  claim 4 , wherein the light solvent contains less than about 25 mole % of methane and ethane. 
     
     
         6 . The method of  claim 1 , wherein step (a) is continued until about 25-30% of the oil in place has been recovered. 
     
     
         7 . The method of  claim 1 , wherein step (b) is continued until about 40-45% of the oil in place has been recovered. 
     
     
         8 . The method of  claim 1 , wherein step (c) is continued until about 56-66%, or about 58-64%, of the oil in place has been recovered. 
     
     
         9 . The method of  claim 1 , wherein step (d) is continued until about 66-72% of the oil in place has been recovered. 
     
     
         10 . The method of  claim 1 , wherein step (e) is continued until about 75-80% of the oil in place has been recovered. 
     
     
         11 . The method of  claim 2 , wherein step (f) is continued until about 85% or more of the oil in place has been recovered. 
     
     
         12 . The method of  claim 1 , wherein, in step (a), the flow rate of the heavy solvent is 0-20% of the flow rate of the steam. 
     
     
         13 . The method of  claim 1 , wherein, in step (a), the flow rate of the heavy solvent is 4-20% of the flow rate of the steam. 
     
     
         14 . The method of  claim 1 , wherein, in step (b), the flow rate of the steam is 8-20% of the steam flow rate of step (a) and wherein the flow rate of the light solvent is 4-8% of the steam flow rate of step (a). 
     
     
         15 . The method of  claim 1 , wherein, in step (c):
 the flow rate of the steam is 20-25% of the steam flow rate of step (a);   the flow rate of the heavy solvent is 0-10% of the steam flow rate of step (a); and   the flow rate of the light solvent is 3-6% of the steam flow rate of step (a).   
     
     
         16 . The method of  claim 1 , wherein, in step (d), the flow rate of the steam is 30-35% of the steam flow rate of step (a). 
     
     
         17 . The method of  claim 1 , wherein, in step (e), the flow rate of the steam is 15-20% of the steam flow rate of step (a) and wherein the flow rate of the light solvent is 2-5% of the steam flow rate of step (a).