Recovery of Hydrocarbons Using Artificial Topseals

Abstract

A method is described for recovering viscous oil such as bitumen from a subsurface formation. The method involves creating an artificial barrier in a subterranean zone above or proximate a top of the subsurface formation. The barrier is largely impermeable to fluid flow. The method also includes reducing the viscosity of the viscous oil and mobilizing hydrocarbons into a readily flowable heavy oil by addition of heat and/or solvent. Heating preferably uses a plurality of heat injection wells. The method further includes producing the heavy oil using a production method that preserves the integrity of the artificial barrier.

1 . A method of recovering a viscous hydrocarbon from a subsurface formation, comprising:
 creating an artificial barrier in a subterranean zone above or proximate a top of the subsurface formation, the barrier being substantially continuous over an area that is at least about five acres (20,232 m 2 ), and is largely impermeable to fluid flow;   reducing the viscosity of the viscous hydrocarbon in at least a portion of the subsurface formation so as to mobilize the viscous hydrocarbon into a flowable heavy oil; and   producing the heavy oil using a production method that maintains the integrity of the artificial barrier.   
     
     
         2 . The method of  claim 1 , wherein reducing the viscosity of the viscous hydrocarbon comprises heating the subsurface formation. 
     
     
         3 . The method of  claim 1 , wherein reducing the viscosity of the viscous hydrocarbon comprises injecting a hydrocarbon solvent into the subsurface formation. 
     
     
         4 . The method of  claim 3 , wherein the hydrocarbon solvent comprises components in the C 3  to C 10  range. 
     
     
         5 . The method of  claim 1 , wherein the viscous hydrocarbon has a viscosity greater than about 1,000 cp in its undisturbed in situ state. 
     
     
         6 . The method of  claim 5 , wherein the viscous hydrocarbon comprises primarily bitumen. 
     
     
         7 . The method of  claim 1 , wherein the artificial barrier is formed above and within about five meters of the top of the subsurface formation. 
     
     
         8 . The method of  claim 7 , wherein:
 reducing the viscosity of the viscous hydrocarbon comprises heating the subsurface formation; and   heating the subsurface formation comprises forming a plurality of heat-supplying wells.   
     
     
         9 . The method of  claim 8 , wherein:
 each of the heat-supplying wells carries an electric current; and   heating the subsurface formation comprises applying electrical-resistive heat to the subsurface formation to reduce the viscosity of the viscous hydrocarbon.   
     
     
         10 . The method of  claim 8 , wherein each of the heat-supplying wells injects a heated fluid. 
     
     
         11 . The method of  claim 10 , wherein the injected fluid is injected at a pressure no greater than about 300 psi above an initial reservoir pressure. 
     
     
         12 . The method of  claim 10 , wherein the injected fluid is injected at a pressure no greater than about 100 psi above an initial reservoir pressure. 
     
     
         13 . The method of  claim 10 , where the heated fluid comprises a vaporized fluid. 
     
     
         14 . The method of  claim 13 , wherein the vaporized fluid comprises steam. 
     
     
         15 . The method of  claim 14 , wherein the vaporized fluid forms a steam chamber from which viscous hydrocarbons gravity-drain to a production well. 
     
     
         16 . The method of  claim 15 , wherein the vaporized fluid further comprises a hydrocarbon solvent. 
     
     
         17 . The method of  claim 16 , wherein the hydrocarbon solvent primarily comprises components in the C 3 -C 5  range. 
     
     
         18 . The method of  claim 16 , wherein the hydrocarbon solvent condenses at initial in situ temperature conditions and in situ pressures. 
     
     
         19 . The method of  claim 8 , wherein:
 producing the heavy oil primarily utilizes gravity drainage; and   production is continuous.   
     
     
         20 . The method of  claim 8 , wherein:
 forming the plurality of heat injection wells comprises forming first horizontal wells to serve as the heat injection wells;   the method further comprises forming second horizontal wells to serve as production wells; and wherein:
 the first and second wells form respective pairs of wells; and 
 the first and second wells are completed substantially within a vertical plane. 
   
     
     
         21 . The method of  claim 7 , wherein creating an artificial barrier comprises injecting a gelling fluid into the subterranean zone, the gelling fluid forming a gel within the subterranean zone after a period of setting. 
     
     
         22 . The method of  claim 21 , wherein:
 the gelling fluid is a polymer solution; and   the polymer solution is injected into the subterranean zone at a pressure below a fracture pressure of the subterranean zone.   
     
     
         23 . The method of  claim 22 , wherein:
 the polymer solution is a cross-linking polymer solution; and   the polymer solution forms the gel as a result of a chemical reaction in situ.   
     
     
         24 . The method of  claim 21 , wherein the gelling fluid has sufficient density to cause it to flow downward and spread over the viscous hydrocarbon proximate the top of the subsurface formation. 
     
     
         25 . The method of  claim 21 , wherein:
 the gelling fluid is a temperature-sensitive emulsion containing wax which at least partially solidifies after injection as a result of cooling in situ; and   the emulsion is injected into the subterranean zone.   
     
     
         26 . The method of  claim 7 , further comprising:
 injecting a fluid into the subterranean zone above a fracture pressure so to form horizontal fractures and to form the artificial barrier.   
     
     
         27 . The method of  claim 26 , wherein the injected fluid is a polymer solution, a clay slurry, or cement. 
     
     
         28 . The method of  claim 7 , wherein creating an artificial barrier comprises injecting a fluid into the subterranean zone, the fluid precipitating solid particles within the subterranean zone and reducing formation permeability. 
     
     
         29 . The method of  claim 7 , wherein creating an artificial barrier comprises:
 completing a plurality of refrigerator wells in the subterranean zone;   circulating a cooling fluid through each of the plurality of refrigerator wells; and   causing water in the subterranean zone to substantially freeze in situ.   
     
     
         30 . The method of  claim 29 , wherein each refrigerator well comprises:
 an elongated tubular member for receiving the cooling fluid and for transporting the cooling fluid to the subterranean zone; and   a first expansion valve in fluid communication with the tubular member through which the cooling fluid flows.   
     
     
         31 . The method of  claim 29 , further comprising:
 chilling the cooling fluid below ambient air temperature prior to circulating the cooling fluid through each of the plurality of refrigerator wells.   
     
     
         32 . The method of  claim 1 , wherein the artificial barrier is substantially continuous over at least 10 acres (40,464 m 2 ). 
     
     
         33 . A method for recovering viscous hydrocarbons from a subsurface formation, comprising:
 locating a permeable subterranean zone geologically above the subsurface formation;   injecting a gelling fluid into the subterranean zone in a liquid phase;   allowing time for the gelling fluid to gel within the subterranean zone and form an artificial topseal over the subsurface formation;   forming a plurality of heat injection wells into the subsurface formation;   forming a plurality of producer wells into the subsurface formation such that each injector well has one or more associated producer wells, thereby creating sets of wells;   injecting steam into each of the plurality of heat injection wells in order to heat the subsurface formation, thereby, (i) creating steam chambers within the subsurface formation, (ii) reducing the viscosity of the viscous hydrocarbons, and (iii) mobilizing the viscous hydrocarbons into a flowable heavy oil; and   producing the heavy oil through each of the plurality of producer wells.   
     
     
         34 . The method of  claim 33 , wherein each of the heat injection wells is completed horizontally within the subsurface formation. 
     
     
         35 . The method of  claim 33 , wherein each of the producer wells is completed horizontally within the subsurface formation. 
     
     
         36 . The method of  claim 34 , wherein:
 each of the heat injection wells is completed horizontally within the subsurface formation;   each of the producer wells is completed horizontally within the subsurface formation, such that each of the sets of wells is a pair of wells; and   each of the pairs of wells is completed substantially within a vertical plane.   
     
     
         37 . The method of  claim 33 , further comprising:
 injecting a hydrocarbon solvent into the subsurface formation with the steam as the steam chambers grow away from the heat injection wells.   
     
     
         38 . The method of  claim 37 , wherein the hydrocarbon solvent comprises hydrocarbon components in the C 3  to C 5  range. 
     
     
         39 . The method of  claim 33 , wherein (i) the temperature of the injected steam is reduced before the steam chamber reaches the artificial topseal, (ii) the composition of the injected steam is modified to include a hydrocarbon solvent after injection has begun, (iii) a pressure at which steam is injected through the heat injection wells is reduced after injection into the subsurface formation has begun, or (iv) combinations thereof, thereby preserving the effectiveness of the artificial topseal. 
     
     
         40 . The method of  claim 33 , wherein the gelling fluid is a cross-linked polymer solution that chemically reacts within the subterranean zone to form a gel. 
     
     
         41 . The method of  claim 33 , wherein:
 the gelling fluid is a waxy, oil-external emulsion comprising oil, added wax, and water;   the waxy emulsion is formulated to be substantially a solid at initial in situ temperature conditions and in situ pressures in the subterranean zone; and   the method further comprises heating the waxy, oil-external emulsion into a flowable liquid at a surface heater before injecting the emulsion into the permeable subterranean zone.   
     
     
         42 . The method of  claim 41 , wherein the water concentration of the waxy emulsion is 40 to 60 volume % of water.