Systems and Methods for Accelerating Production of Viscous Hydrocarbons in a Subterranean Reservoir with Thermally Activated Chemical Agents

Abstract

A method for mobilizing viscous hydrocarbons in a reservoir includes (a) injecting an aqueous solution into the reservoir with the reservoir at the reservoir ambient temperature. The aqueous solution includes water and a water-soluble chemical agent that is substantially non-decomposable and substantially non-reactive in the reservoir at the reservoir ambient temperature. In addition, the method includes (b) adding thermal energy to the reservoir at any time after (a) to increase the temperature of at least a portion of the reservoir to an elevated temperature greater than the ambient temperature of the reservoir. Further, the method includes (c) in response to the elevated temperature in (b), mobilizing at least a portion of the hydrocarbons in the reservoir by reducing the viscosity of the hydrocarbons and allowing the chemical agent to enhance mobilization of the hydrocarbons.

What is claimed is: 
     
         1 . A method for mobilizing viscous hydrocarbons in a reservoir in a subterranean formation, the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) injecting an aqueous solution into the reservoir with the reservoir at the ambient temperature, wherein the aqueous solution comprises water and a water-soluble chemical agent that is substantially non-decomposable and substantially non-reactive in the reservoir at the ambient temperature of the reservoir; and   (b) adding thermal energy to the reservoir at any time after (a) to increase the temperature of at least a portion of the reservoir to an elevated temperature greater than the ambient temperature of the reservoir;   (c) in response to the elevated temperature in (b), mobilizing at least a portion of the hydrocarbons in the reservoir by reducing the viscosity of the hydrocarbons and allowing the chemical agent to enhance mobilization of the hydrocarbons.   
     
     
         2 . The method of  claim 1 , wherein the hydrocarbons have a viscosity greater than 10,000 cP before (b);
 wherein (c) comprises decreasing the viscosity of the hydrocarbons to a viscosity less than 10,000 cP.   
     
     
         3 . The method of  claim 1 , wherein (b) is performed within 50 days after (a). 
     
     
         4 . The method of  claim 3 , wherein (b) is performed immediately after (a). 
     
     
         5 . The method of  claim 1 , wherein the aqueous solution is injected at an injection pressure during (a) that is greater than the ambient pressure of the reservoir and below a fracturing pressure of the formation. 
     
     
         6 . The method of  claim 5 , wherein the injection pressure is less than a displacement pressure of the hydrocarbons in the reservoir. 
     
     
         7 . The method of  claim 5 , further comprising pulsing the injection pressure during (a). 
     
     
         8 . The method of  claim 1 , wherein the chemical agent is a surfactant or a thermally activated chemical species, wherein the surfactant emulsifies the mobilized hydrocarbons at the elevated temperature and the thermally activated chemical species decomposes or reacts at the elevated temperature. 
     
     
         9 . The method of  claim 8 , wherein the elevated temperature is between 40° and 200° C. 
     
     
         10 . The method of  claim 9 , wherein the chemical agent is urea. 
     
     
         11 . The method of  claim 9 , wherein the chemical agent comprises an alkali metal carbonate or a metaborate salt of an alkali metal. 
     
     
         12 . The method of  claim 11 , wherein the aqueous solution comprises a metal chelating agent. 
     
     
         13 . The method of  claim 1 , further comprises:
 determining a salt concentration and a salt composition in the reservoir;   forming a brine having a salt concentration and a salt composition analogous to the salt concentration and the salt composition of the reservoir; and   mixing the chemical agent and the brine to form the aqueous solution prior to (a).   
     
     
         14 . The method of  claim 1 , wherein (b) comprises injecting steam into the reservoir. 
     
     
         15 . The method of  claim 14 , wherein the steam injected into the reservoir has a steam quality less than 100% and comprises a liquid phase and a vapor phase;
 wherein (b) comprises:
 delivering a water-soluble surfactant to the reservoir in the liquid phase of the steam; and 
 injecting the water-soluble surfactant and the steam into the reservoir at the same time. 
   
     
     
         16 . The method of  claim 15 , wherein (b) further comprises:
 delivering a water-soluble thermally activated chemical species to the reservoir in the liquid phase of the steam; and   injecting the water-soluble thermally activated chemical species and the steam into the reservoir at the same time.   
     
     
         17 . The method of  claim 15 , wherein the water-soluble chemical agent injected into the reservoir during (a) is different than the water-soluble surfactant injected into the reservoir with the steam in (b). 
     
     
         18 . The method of  claim 14 , wherein the steam injected into the reservoir has a steam quality less than 100% and comprises a liquid phase and a vapor phase;
 wherein (b) comprises:
 delivering a water-soluble thermally activated chemical species to the reservoir in the liquid phase of the steam; and 
 injecting the water-soluble thermally activated chemical species and the steam into the reservoir at the same time. 
   
     
     
         19 . The method of  claim 18 , wherein the liquid phase of the steam has a temperature, and wherein the water-soluble thermally activated chemical species has a conversion rate less than 10 mol % over a time period less than 10 minutes in the presence of the steam and at the temperature of the liquid phase. 
     
     
         20 . The method of  claim 18 , wherein the water-soluble chemical agent injected into the reservoir during (a) is different than the water-soluble thermally activated chemical species injected into the reservoir with the steam in (b). 
     
     
         21 . The method of  claim 1 , wherein (a) comprises injecting the aqueous solution into the reservoir through a first well extending through the reservoir. 
     
     
         22 . The method of  claim 21 , wherein (a) comprises simultaneously injecting the aqueous solution into the reservoir through the first well and a second well extending through the reservoir. 
     
     
         23 . A method for mobilizing viscous hydrocarbons in a reservoir in a subterranean formation, the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) injecting an aqueous solution into the reservoir through an injection well or a production well of a SAGD well pair, wherein the reservoir is at the ambient temperature, and wherein the aqueous solution comprises water and a water-soluble chemical agent that is substantially non-decomposable and substantially non-reactive in the reservoir at the ambient temperature of the reservoir; and   (b) injecting steam into the reservoir after (a) through the injection well or the production well to increase the temperature of at least a portion of the reservoir to an elevated temperature greater than the ambient temperature of the reservoir;   (c) in response to the elevated temperature in (b), mobilizing at least a portion of the hydrocarbons in the reservoir by reducing the viscosity of the hydrocarbons and allowing the chemical agent to enhance mobilization of the hydrocarbons.   
     
     
         24 . The method of  claim 23 , further comprising:
 (d) injecting steam into the reservoir after (b) through the injection well;   (e) collecting hydrocarbons in the production well during (d); and   (f) producing the collected hydrocarbons in the production well to the surface.   
     
     
         25 . The method of  claim 23 , wherein the hydrocarbons in the reservoir have a viscosity greater than 10,000 cP before (b);
 wherein (c) comprises decreasing the viscosity of the hydrocarbons between the injection well and the production well to a viscosity less than 10,000 cP.   
     
     
         26 . The method of  claim 23 , wherein (b) is performed less than 50 days after (a). 
     
     
         27 . The method of  claim 26 , wherein (b) is performed immediately after (a). 
     
     
         28 . The method of  claim 23 , wherein (a) comprises:
 (a1) injecting the aqueous solution into the reservoir through both the injection well and the production well of the SAGD well pair.   
     
     
         29 . The method of  claim 28 , wherein (a) further comprises:
 (a2) injecting the aqueous solution into the reservoir only through the injection well after (a1).   
     
     
         30 . The method of  claim 23 , wherein (a) comprises injecting the aqueous solution into the reservoir at a pressure that is greater than the ambient pressure of the reservoir and below a fracturing pressure of the formation. 
     
     
         31 . The method of  claim 30 , further comprising varying the pressure of the aqueous solution during (a). 
     
     
         32 . The method of  claim 23 , wherein (c) comprises decomposing the chemical agent with thermal energy from the steam or reacting the chemical agent with the hydrocarbons. 
     
     
         33 . The method of  claim 23 , wherein the chemical agent is a surfactant or a thermally activated chemical species, wherein the surfactant emulsifies the mobilized hydrocarbons and the thermally activated chemical species decomposes or reacts at the elevated temperature. 
     
     
         34 . The method of  claim 33 , wherein the elevated temperature is between 40° and 200° C. 
     
     
         35 . The method of  claim 23 , wherein the chemical agent comprises urea. 
     
     
         36 . The method of  claim 33 , wherein the chemical agent comprises an alkali metal carbonate or a metaborate salt of an alkali metal. 
     
     
         37 . The method of  claim 36 , wherein the aqueous solution comprises a metal chelating agent to the aqueous solution during (a). 
     
     
         38 . The method of  claim 24 , wherein the steam injected into the reservoir during (d) has a steam quality less than 100% and comprises a liquid phase and a vapor phase;
 wherein (d) further comprises:
 delivering a water-soluble surfactant to the reservoir in the liquid phase of the steam; and 
 injecting the water-soluble surfactant and the steam into the reservoir at the same time. 
   
     
     
         39 . The method of  claim 38 , wherein (d) further comprises:
 delivering a water-soluble thermally activated chemical species to the reservoir in the liquid phase of the steam; and   injecting the water-soluble thermally activated chemical species and the steam into the reservoir at the same time.   
     
     
         40 . The method of  claim 38 , wherein the water-soluble chemical agent injected into the reservoir during (a) is different than the water-soluble surfactant injected into the reservoir with the steam during (d). 
     
     
         41 . The method of  claim 24 , wherein the steam injected into the reservoir during (d) has a steam quality less than 100% and comprises a liquid phase and a vapor phase;
 wherein (d) further comprises:
 delivering a water-soluble thermally activated chemical species to the reservoir in the liquid phase of the steam; and 
 injecting the water-soluble thermally activated chemical species and the steam into the reservoir at the same time. 
   
     
     
         42 . The method of  claim 41 , wherein the liquid phase of the steam has a temperature, and wherein the water-soluble thermally activated chemical species has a conversion rate less than 10 mol % over a time period less than 10 minutes in the presence of the steam and at the temperature of the liquid phase. 
     
     
         43 . The method of  claim 41 , wherein the water-soluble chemical agent injected into the reservoir during (a) is different than the water-soluble thermally activated chemical species injected into the reservoir with the steam during (d). 
     
     
         44 . A method for mobilizing viscous hydrocarbons from a reservoir in a subterranean formation, the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) injecting a volume of an aqueous solution into the reservoir with the reservoir at the ambient temperature, wherein the aqueous solution comprises a brine and a water-soluble chemical agent that is substantially non-decomposable and substantially non-reactive in the reservoir at the ambient temperature of the reservoir, wherein the chemical agent in the aqueous solution has a concentration greater than or equal to 0.01 wt % and less than the solubility limit of the chemical agent in the brine at the ambient temperature of the reservoir, and wherein the volume is based on a pore volume of connate water in a portion of the reservoir to be produced;   (b) adding thermal energy to the reservoir at any time after (a) to increase the temperature of at least a portion of the reservoir to an elevated temperature greater than the ambient temperature of the reservoir;   (c) in response to the elevated temperature in (b), mobilizing at least a portion of the hydrocarbons in the reservoir and allowing the chemical agent to enhance mobilization of the hydrocarbons.   
     
     
         45 . The method of  claim 44 , wherein the volume is at least equal to the pore volume of connate water in the portion of the reservoir to be produced. 
     
     
         46 . The method of  claim 44 , wherein (a) comprises injecting the aqueous solution at a pressure that is greater than the ambient pressure of the reservoir and less than a fracture pressure of the formation. 
     
     
         47 . The method of  claim 44 , wherein the chemical agent is a surfactant or a thermally activated chemical species, wherein the surfactant emulsifies the mobilized hydrocarbons at the elevated temperature and the thermally activated chemical species decomposes or reacts at the elevated temperature. 
     
     
         48 . The method of  claim 47 , wherein the elevated temperature is between 40° and 200° C. 
     
     
         49 . The method of  claim 47 , wherein the chemical agent is urea. 
     
     
         50 . The method of  claim 47 , wherein the chemical agent comprises an alkali metal carbonate or a metaborate salt of an alkali metal. 
     
     
         51 . The method of  claim 50 , wherein the aqueous solution further comprises a metal chelating agent. 
     
     
         52 . The method of  claim 44 , wherein the hydrocarbons are immobile in the reservoir before (b). 
     
     
         53 . The method of  claim 52 , wherein the hydrocarbons in the reservoir have a viscosity greater than 10,000 cP before (b);
 wherein (c) comprises decreasing the viscosity of the viscous hydrocarbons to a viscosity less than 10,000 cP.   
     
     
         54 . The method of  claim 44 , wherein (a) comprises injecting the volume of the aqueous solution into the reservoir through an injection well or a production well of a SAGD well pair;
 wherein (b) comprises injecting steam into the reservoir through the injection well or the production well.   
     
     
         55 . The method of  claim 54 , further comprising:
 (d) injecting steam into the reservoir after (b) through the injection well;   (e) collecting hydrocarbons in the production well during (d); and   (f) producing the collected hydrocarbons in the production well to the surface.   
     
     
         56 . A method for mobilizing viscous hydrocarbons in a reservoir in a subterranean formation, the method comprising:
 (a) injecting steam into the reservoir, wherein the steam has a steam quality less than 100% and comprises a liquid phase and a vapor phase, wherein injecting the steam comprises delivering an aqueous solution to the reservoir in the liquid phase of the steam and injecting the aqueous solution into the reservoir with the steam, wherein the aqueous solution comprises a surfactant;   (b) in response to the steam injected in (a), mobilizing the hydrocarbons in the reservoir by reducing the viscosity of the hydrocarbons;   (c) emulsifying the hydrocarbons with the surfactant during (b) to enhance the mobilization of the hydrocarbons.   
     
     
         57 . The method of  claim 56 , further comprising:
 (d) collecting mobilized hydrocarbons in a production well of a SAGD well pair; and   (e) producing the collected hydrocarbons in the production well to the surface.   
     
     
         58 . The method of  claim 57 , further comprising injecting the aqueous solution into the reservoir with the steam during (a) and before (e). 
     
     
         59 . The method of  claim 57 , further comprising injecting the surfactant into the reservoir with the steam during (e). 
     
     
         60 . The method of  claim 56 , wherein (a) comprises injecting the steam into the reservoir through an injection well or a production well of a SAGD well pair. 
     
     
         61 . The method of  claim 60 , wherein (a) comprises injecting the steam into the reservoir through both the injection well and the production well. 
     
     
         62 . The method of  claim 60 , wherein (a) comprises injecting the steam into the reservoir through the injection well and injecting the aqueous solution into the reservoir through the injection well. 
     
     
         63 . The method of  claim 56 , wherein (a) further comprises:
 delivering an aqueous solution comprising a water-soluble thermally activated chemical species to the reservoir in the liquid phase of the steam and injecting the aqueous solution comprising the water-soluble thermally activated chemical species and the steam into the reservoir at the same time.   
     
     
         64 . A method for mobilizing viscous hydrocarbons in a reservoir in a subterranean formation, the method comprising:
 (a) injecting steam into the reservoir, wherein the steam has a steam quality less than 100% and comprises a liquid phase and a vapor phase, wherein injecting the steam comprises delivering an aqueous solution to the reservoir in the liquid phase of the steam and injecting the aqueous into the reservoir with the steam during (a), wherein the aqueous solution comprises a non-volatile thermally activated chemical species, wherein the liquid phase of the steam has a temperature, and wherein the thermally activated chemical species has a conversion rate less than 10 mol % over a time period less than 10 minutes in the presence of the steam and at the temperature of the liquid phase; and   (b) decomposing or reacting the thermally activated chemical species in the reservoir to enhance the mobilization of the viscous hydrocarbons.   
     
     
         65 . The method of  claim 64 , wherein the thermally activated chemical species decomposes or reacts at a temperature between 40° and 200° C. 
     
     
         66 . The method of  claim 64 , further comprising:
 (c) collecting mobilized hydrocarbons in a production well of a SAGD well pair; and   (d) producing the collected hydrocarbons in the production well to the surface.   
     
     
         67 . The method of  claim 66 , further comprising injecting the aqueous solution into the reservoir with the steam during (a) and before (d). 
     
     
         68 . The method of  claim 66 , further comprising injecting the aqueous solution into the reservoir with the steam during (d). 
     
     
         69 . The method of  claim 64 , wherein (a) comprises injecting the steam into the reservoir through an injection well or a production well of a SAGD well pair. 
     
     
         70 . The method of  claim 69 , wherein (a) comprises injecting the steam into the reservoir through both the injection well and the production well. 
     
     
         71 . The method of  claim 69 , wherein (a) comprises injecting the steam into the reservoir through the injection well and injecting the aqueous solution into the reservoir through the injection well. 
     
     
         72 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation using steam assisted gravity drainage (SAGD), the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) during a loading phase, loading a portion of the reservoir with an aqueous solution injected into the reservoir through an injection well or a production well of a SAGD well pair, wherein the reservoir is at the ambient temperature, and wherein the aqueous solution comprises water and a water-soluble chemical agent that is substantially non-decomposable and substantially non-reactive in the reservoir at the ambient temperature of the reservoir;   (b) at any time after the loading phase in (a), commencing a start-up phase wherein steam is injected into the reservoir through the injection well or the production well to increase the temperature of the portion of the reservoir to an elevated temperature greater than the ambient temperature of the reservoir;   (c) in response to the elevated temperature in (b), mobilizing at least a portion of the hydrocarbons in the reservoir by reducing the viscosity of the hydrocarbons and allowing the chemical agent to enhance mobilization of the hydrocarbons   (d) continuing the start-up phase until fluid communication between the injection well and the production well is achieved;   (e) in response to (d), ceasing the start-up phase and commencing a production phase wherein steam is injected into the reservoir through the injection well and at least a portion of the hydrocarbons are produced from the reservoir through the production well.   
     
     
         73 . The method of  claim 72 , wherein the hydrocarbons in the reservoir have a viscosity greater than 10,000 cP before (b);
 wherein (c) comprises decreasing the viscosity of the hydrocarbons between the injection well and the production well to a viscosity less than 10,000 cP   
     
     
         74 . The method of  claim 72 , wherein (b) is performed less than 50 days after (a). 
     
     
         75 . The method of  claim 74 , wherein (b) is performed immediately after (a). 
     
     
         76 . The method of  claim 72 , wherein the elevated temperature is between 40° and 200° C. 
     
     
         77 . The method of  claim 72 , wherein the chemical agent comprises urea. 
     
     
         78 . The method of  claim 72 , wherein the chemical agent comprises an alkali metal carbonate or a metaborate salt of an alkali metal. 
     
     
         79 . The method of  claim 72 , wherein the steam injected during (b) has a quality less than 100% and includes a vapor phase and a liquid phase;
 wherein (b) further comprises injecting a surfactant into the reservoir via the liquid phase of the steam.   
     
     
         80 . The method of  claim 72 , wherein the steam injected during (d) has a quality less than 100% and includes a vapor phase and a liquid phase
 wherein (d) further comprises injecting a surfactant into the reservoir via the liquid phase of the steam.