Method for producing heavy oil

Abstract

A method is provided for production of heavy oil from a reservoir containing heavy oil, the method including the steps of: providing a plurality of wells into the formation; injecting into the plurality of wells a mixture comprising steam and a solvent; ceasing injection of the mixture; producing a mixture of heavy oil, solvent and condensed steam from the plurality of wells after injection of steam has ceased: and after production of the mixture of heavy oil, solvent and condensate from at least one of the plurality of wells has declined to a predetermined rate, injecting into the at least one well a stream consisting essentially of steam while at least one other well continues to operate as a producing well.

What is claimed is: 
     
         1 . A method for production of heavy oil from a reservoir containing heavy oil, the method comprising the steps of:
 providing a plurality of wells into the formation;   injecting into the plurality of wells a mixture comprising steam and a solvent;   ceasing injection of the mixture;   producing a mixture of heavy oil, solvent and condensed steam from the plurality of wells after injection of steam has ceased: and   after production of the mixture of heavy oil, solvent and condensate from at least one of the plurality of wells has declined to a predetermined rate, injecting into the at least one well a stream consisting essentially of steam while at least one other well continues to operate as a producing well.   
     
     
         2 . The method of  claim 1 , wherein the solvent comprises a hydrocarbon solvent. 
     
     
         3 . The method of  claim 1 , wherein the solvent comprises a solvent comprising five and six carbon hydrocarbons. 
     
     
         4 . The method of  claim 1 , wherein at least one of the wells that continue to operate as a producer well extends to a lower portion of the reservoir. 
     
     
         5 . The method of  claim 1 , wherein at least one of the wells through which the stream consisting essentially of steam is injected extends to an upper portion of the reservoir. 
     
     
         6 . The method of  claim 1 , wherein the steps of injecting into the plurality of wells a mixture comprising steam and a solvent; ceasing injection of the mixture; and producing a mixture of heavy oil, solvent and condensed steam from the plurality of wells after injection of steam has ceased; are repeated in this order for a plurality of cycles. 
     
     
         7 . The method of  claim 1 , wherein the mixture comprising steam and a solvent comprises between 85 and 99 percent steam and between 1 and 15 percent solvent based on a condensed volumes of steam and solvent. 
     
     
         8 . The method of  claim 7 , wherein the mixture comprising steam and a solvent comprises between 94 and 98 percent steam and between 2 and 6 percent solvent based on a condensed volumes of steam and solvent. 
     
     
         9 . The method of  claim 8 , wherein the produced heavy oil comprises less than ten percent by weight asphaltenes. 
     
     
         10 . The method of  claim 1 , wherein the wells, within the reservoir comprise essentially horizontal portions of wells. 
     
     
         11 . The method of  claim 10 , wherein the well comprising an essentially horizontal portion of the well is a well that continues to operate as a production well, and the essentially horizontal portion extends through a lower portion of the reservoir. 
     
     
         12 . The method of  claim 10 , wherein the well comprising an essentially horizontal portion of the well is a well through which the stream consisting essentially of steam is injected, and the essentially horizontal portion extends through a lower portion of the reservoir. 
     
     
         13 . The method of  claim 1 , wherein the wells are essentially vertical wells. 
     
     
         14 . The method of  claim 13 , wherein the ratio of wells that continue to operate as production wells to wells through which the stream consisting essentially of steam is injected is between about 2 and about 10. 
     
     
         15 . The method of  claim 14 , wherein the ratio of wells that continue to operate as production wells to wells through which the stream consisting essentially of steam is injected is about two, and the wells are in an essentially hexagonal pattern with each injection well surrounded by six producing wells.