Systems and Methods for the Production of a Subterranean Reservoir Containing Viscous Hydrocarbons

Abstract

A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation includes (a) injecting steam into the reservoir. In addition, the method includes (b) injecting a thermally activated chemical species into the reservoir with the steam during (a). The thermally activated chemical species decomposes at a temperature between 40° and 200° C. Further, the method includes (c) decreasing the viscosity of the hydrocarbons in the reservoir during (a) and (b). Still further, the method includes (d) mobilizing at least some of the hydrocarbons in the reservoir.

What is claimed is: 
     
         1 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) selecting a pretreatment agent that is water-soluble and substantially non-reactive in the reservoir at the ambient temperature of the reservoir;   (b) forming an aqueous pretreatment solution with the pretreatment agent;   (c) injecting the aqueous pretreatment solution into the reservoir at a temperature less than or equal to the ambient temperature of the reservoir; and   (d) adding thermal energy to the reservoir to increase the temperature of the reservoir to an operating temperature after (c).   
     
     
         2 . The method of  claim 1 , wherein (d) is performed immediately after (c). 
     
     
         3 . The method of  claim 1 , wherein the aqueous pretreatment solution is injected at an injection pressure during (c);
 wherein that the injection pressure is greater than the ambient pressure of the reservoir and below a fracturing pressure of the formation.   
     
     
         4 . The method of  claim 3 , wherein that the injection pressure is less than a displacement pressure of the viscous hydrocarbons in the reservoir. 
     
     
         5 . The method of  claim 3 , further comprising pulsing the injection pressure during (c). 
     
     
         6 . The method of  claim 1 , wherein the pretreatment agent is a surfactant or a thermally activated chemical species that activates at an activation temperature greater than the ambient temperature of the reservoir temperature and less than the operating temperature. 
     
     
         7 . The method of  claim 6 , wherein the activation temperature is between 40° and 200° C. 
     
     
         8 . The method of  claim 7 , wherein the pretreatment agent is urea. 
     
     
         9 . The method of  claim 1 , wherein (b) comprises:
 (b1) determining a salt concentration and a salt composition in the reservoir;   (b2) forming a brine having a salt concentration and a salt composition analogous to the salt concentration and the salt composition of the reservoir;   (b3) mixing the pretreatment agent and the brine.   
     
     
         10 . The method of  claim 1 , wherein (d) comprises injecting steam into the reservoir. 
     
     
         11 . The method of  claim 10 , wherein (d) comprises injecting steam and a thermally activated chemical species into the reservoir at the same time, wherein the thermally activated chemical species injected with steam activates at an activation temperature less than the operating temperature. 
     
     
         12 . The method of  claim 1 , wherein (c) comprises injecting the aqueous pretreatment solution into the reservoir through a first well extending through the reservoir or through the first well and a second well extending through the reservoir. 
     
     
         13 . The method of  claim 1 , wherein (a) comprises selecting a plurality of pretreatment agents, wherein each pretreatment agent is water-soluble and inert at the ambient temperature of the reservoir; and
 wherein (b) comprises forming the aqueous pretreatment solution with the plurality of pretreatment agents.   
     
     
         14 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) forming a SAGD well pair extending through the formation, wherein the SAGD well pair includes an injection well and a production well, wherein each well has a vertical section extending from the surface of the formation and a horizontal section traversing the reservoir;   (b) forming an aqueous pretreatment solution with one or more pretreatment agents, wherein each pretreatment agent is water-soluble and substantially non-reactive in the reservoir at the ambient temperature of the reservoir;   (c) injecting the aqueous pretreatment solution into the reservoir at a temperature less than or equal to the ambient reservoir temperature; and   (d) injecting steam into the reservoir after (c) to increase the temperature of the reservoir to a SAGD operating temperature.   
     
     
         15 . The method of  claim 14 , wherein (c) comprises:
 (c1) pumping the aqueous pretreatment solution through the horizontal section of the production well and the horizontal section of the injection well at the same time.   
     
     
         16 . The method of  claim 15 , wherein (c) further comprises:
 (c2) pumping the aqueous pretreatment solution through the horizontal section of the production well after (c1).   
     
     
         17 . The method of  claim 14 , wherein (c) comprises injecting the aqueous solution at a pressure that is greater than the ambient pressure of the reservoir and below a fracturing pressure of the formation. 
     
     
         18 . The method of  claim 17 , further comprising varying the pressure of the aqueous solution during (c). 
     
     
         19 . The method of  claim 14 , wherein (d) comprises:
 (d1) decreasing the viscosity of the hydrocarbons in the reservoir with thermal energy from the steam;   (d2) decomposing the pretreatment agent with thermal energy from the steam;   (d3) mobilizing at least some of the hydrocarbons in the reservoir during (d1) and (d2).   
     
     
         20 . The method of  claim 19 , further comprising:
 collecting mobilized hydrocarbons in the horizontal section of the production well; and   producing the collected hydrocarbons in the production well to the surface.   
     
     
         21 . The method of  claim 14 , wherein (d) is performed immediately after (c). 
     
     
         22 . The method of  claim 14 , wherein the pretreatment agent is a surfactant or a thermally activated chemical species that activates at an activation temperature greater than the ambient temperature of the reservoir temperature and less than the SAGD operating temperature. 
     
     
         23 . The method of  claim 22 , wherein the activation temperature is between 40° and 200° C. 
     
     
         24 . The method of  claim 14 , wherein at least one of the one or more pretreatment agents is urea. 
     
     
         25 . The method of  claim 14 , further comprising injecting a thermally activated chemical species into the reservoir with the steam during (d), wherein the thermally activated chemical species injected with steam during (d) activates at an activation temperature less than the SAGD operating temperature. 
     
     
         26 . The method of  claim 20 , further comprising injecting a thermally activated chemical species into the reservoir with steam while producing the collected hydrocarbons in the production well to the surface, wherein the thermally activated chemical species injected while producing the collected hydrocarbons activates at an activation temperature less than the SAGD operating temperature. 
     
     
         27 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the reservoir having an ambient temperature and an ambient pressure, the method comprising:
 (a) selecting one or more pretreatment agents, wherein each pretreatment agent is water-soluble and non-reactive or substantially non-reactive in the reservoir at the ambient temperature of the reservoir;   (b) mixing the one or more pretreatment agents with a brine to form an aqueous pretreatment solution, wherein each pretreatment agent in the aqueous pretreatment solution has a concentration greater than or equal to 0.01 wt % and less than the solubility limit of the pretreatment agent in the brine;   (c) determining a volume of the reservoir to be pretreated and determining a pore volume of the connate water in the portion of the reservoir to be treated; and   (d) injecting a volume of the aqueous pretreatment solution into the reservoir at the ambient reservoir temperature, wherein the volume is at least equal to the pore volume of the connate water in the portion of the reservoir to be pretreated.   
     
     
         28 . The method of  claim 27 , wherein (d) comprises injecting the aqueous pretreatment solution at a pressure that is greater than the ambient pressure of the reservoir and less than a fracture pressure of the formation. 
     
     
         29 . The method of  claim 27 , wherein the volume of the injected aqueous pretreatment solution is about two times the pore volume of the connate water in the portion of the reservoir to be pretreated. 
     
     
         30 . The method of  claim 27 , further comprising:
 increasing the temperature of the reservoir to a thermal recovery operating temperature;   wherein the pretreatment agent is a surfactant or a thermally activated chemical species that activates at an activation temperature greater than the ambient temperature of the reservoir temperature and less than the thermal recovery operating temperature.   
     
     
         31 . The method of  claim 30 , wherein the activation temperature is between 40° and 200° C. 
     
     
         32 . The method of  claim 30 , wherein at least one of the one or more pretreatment agents is urea. 
     
     
         33 . A method for recovering viscous hydrocarbons from a reservoir in a subterranean formation, the method comprising:
 (a) injecting steam into the reservoir;   (b) injecting a thermally activated chemical species into the reservoir with the steam during (a), wherein the thermally activated chemical species decomposes at a temperature between 40° and 200° C.;   (c) decreasing the viscosity of the hydrocarbons in the reservoir during (a) and (b);   (d) mobilizing at least some of the hydrocarbons in the reservoir.   
     
     
         34 . The method of  claim 33 , wherein the thermally activated chemical species decomposes at a temperature between 80° and 150° C. 
     
     
         35 . The method of  claim 33 , further comprising:
 (e) collecting mobilized hydrocarbons in the horizontal section of the production well; and   (f) producing the collected hydrocarbons in the production well to the surface.   
     
     
         36 . The method of  claim 35 , further comprising injecting the thermally activated chemical species into the reservoir with the steam during (a) before (f) or during (g). 
     
     
         37 . The method of  claim 33 , further comprising:
 (a) forming a SAGD well pair extending through the formation, wherein the SAGD well pair includes an injection well and a production well, wherein each well has a vertical section extending from the surface of the formation and a horizontal section traversing the reservoir;   wherein (a) comprises injecting steam into the reservoir from the horizontal section of the injection well;   wherein (b) comprises injecting the thermally activated chemical species into the reservoir from the horizontal section of the injection well.