Systems and methods for producing viscous hydrocarbons

Abstract

An embodiment of a method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the method including (a) continuously injecting steam into the formation, (b) injecting a first amount of a solvent into the formation for a first period of time during (a), and (c) stopping the injection of the solvent during (a) and after (b). In addition, the method includes (d) determining the effectiveness of the solvent injected during (b), and (e) injecting a second amount of the solvent into the formation during a second period of time during (a). The second amount is chosen based on the determination in (d). Further, the method includes (f) reducing a viscosity of the hydrocarbons within the reservoir with the solvent during (b) and (e).

What is claimed is: 
     
         1 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the method comprising:
 (a) continuously injecting steam into the formation;   (b) injecting a first amount of a solvent into the formation for a first period of time during (a);   (c) stopping the injection of the solvent during (a) and after (b);   (d) determining the effectiveness of the solvent injected during (b);   (e) injecting a second amount of the solvent into the formation during a second period of time during (a), wherein the second amount is chosen based on the determination in (d); and   (f) reducing a viscosity of the hydrocarbons within the reservoir with the solvent during (b) and (e).   
     
     
         2 . The method of  claim 1 , wherein (d) comprises:
 (d1) monitoring a temperature of the reservoir after (b); and   (d2) estimating the viscosity of the hydrocarbons in the reservoir based on the temperature monitored in (d1).   
     
     
         3 . The method of  claim 1 , wherein (d) comprises monitoring a production rate of the hydrocarbons. 
     
     
         4 . The method of  claim 1 , wherein the first amount of solvent in (b) is greater than the second amount of solvent (e). 
     
     
         5 . The method of  claim 4 , wherein (b) further comprises injecting the solvent at a first rate of injection; wherein (e) further comprises injecting the solvent at a second rate of injection; and wherein the first rate of injection is greater than the second rate of injection. 
     
     
         6 . The method of  claim 4 , wherein (b) further comprises injecting the solvent at a first solvent-to-steam ratio; wherein (e) further comprises injecting the solvent at a second solvent-to-steam ratio; and wherein the first solvent-to-steam ratio is greater than the second solvent-to-steam ratio. 
     
     
         7 . The method of  claim 4 , wherein the first period of time in (b) is greater than the second period of time in (e). 
     
     
         8 . The method of  claim 1 , wherein (a) further comprises maintaining an injection rate of steam within +/−25% of a desired injection rate. 
     
     
         9 . The method of  claim 1 , wherein both (b) and (e) comprise injecting the solvent in a vapor phase. 
     
     
         10 . The method of  claim 1 , wherein the solvent comprises hydrocarbons that have a viscosity that is less than the viscosity of the hydrocarbons within the reservoir. 
     
     
         11 . The method of  claim 1 , further comprising:
 (g) stopping the injection of the solvent during (a) and after (e);   (h) determining the effectiveness of the injection in (e); and   (i) injecting a third amount of solvent into the formation during a third period of time during (a), wherein the third amount is chosen based on the determination in (h).   
     
     
         12 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the method comprising:
 (a) continuously injecting steam into the formation through an injection well;   (b) maintaining the injection of steam in (a) within +1-25% of a desired injection rate;   (c) producing the hydrocarbons to the surface through a production well extending within the formation;   (d) injecting a first amount of a solvent into the formation for a first period of time during (a);   (e) stopping the injection of the solvent during (a) and after (d);   (f) injecting a second amount of the solvent into the formation during a second period of time during (a) and after (e); and   (g) reducing a viscosity of the hydrocarbons within the reservoir with the solvent during (d) and (f).   
     
     
         13 . The method of  claim 12 , wherein the first amount of the solvent in (d) is greater than the second amount of the solvent (f). 
     
     
         14 . The method of  claim 13 , wherein (d) further comprises injecting the solvent at a first rate of injection; wherein (f) further comprises injecting the solvent at a second rate of injection; and wherein the first rate of injection is greater than the second rate of injection. 
     
     
         15 . The method of  claim 13 , wherein (d) further comprises injecting the solvent at a first solvent-to-steam ratio; wherein (f) further comprises injecting the solvent at a second solvent-to-steam ratio; and wherein the first solvent-to-steam ratio is greater than the second solvent-to-steam ratio. 
     
     
         16 . The method of  claim 13 , wherein the first period of time in (d) is greater than the second period of time in (f). 
     
     
         17 . The method of  claim 12 , wherein the solvent comprises a hydrocarbon that has a viscosity that is less than the viscosity of the hydrocarbons within the reservoir. 
     
     
         18 . The method of  claim 12 , further comprising:
 (h) stopping the injection of the solvent during (a) and after (f); and   (i) injecting a third amount of solvent into the formation during a third period of time during (a).   
     
     
         19 . The method of  claim 12 , wherein both (d) and (f) comprise injecting the solvent in a vapor phase. 
     
     
         20 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the method comprising:
 (a) continuously injecting steam into the formation;   (b) injecting a first amount of a solvent into the formation for a first period of time during (a);   (c) stopping the injection of the solvent during (a) and after (b);   (d) monitoring a rate of production of the hydrocarbons from the reservoir to the surface after (b);   (e) injecting a second amount of the solvent into the formation during a second period of time during (a), wherein the second amount is chosen based on the rate of production monitored in (d); and   (f) reducing a viscosity of the hydrocarbons within the reservoir with the solvent during (b) and (e).