Thermal hydrocarbon recovery method using shock cycling fluid stimulation

Abstract

A thermal hydrocarbon recovery method comprising cycling high pressure fluid injection for a period of time followed by low pressure fluid injection for a period of time, the high pressure injection primarily to dilate and enhance reservoir porosity/permeability and improve the subsequent low pressure fluid injectivity. The method is particularly useful for recovering heavy and extra heavy hydrocarbons from tight formations and/or low vertical permeability reservoirs under viscosity reduction and gravity drainage methods. This method is believed to be applicable for recovering heavy or extra heavy oil from reservoirs with geological risk associated with cap rock integrity.

What is claimed is: 
     
         1 . A method for recovering hydrocarbon from a subsurface reservoir, the method comprising the steps of:
 a. drilling a wellbore from surface to the reservoir;   b. injecting a first fluid down the wellbore under a first pressure, the first fluid at the first pressure sufficient to substantially dilate at least a portion of the reservoir;   c. subsequently injecting a second fluid down the wellbore under a second pressure, the second pressure lower than the first pressure and the second fluid at the second pressure insufficient to substantially further dilate the at least a portion of the reservoir;   d. allowing the second fluid to mobilize the hydrocarbon in the reservoir; and   e. producing the hydrocarbon to the surface.   
     
     
         2 . The method of  claim 1  wherein the step of injecting the first fluid is for a first period of time, and the step of injecting the second fluid is for a second period of time, the first period of time being lesser than the second period of time. 
     
     
         3 . The method of  claim 1  wherein the step of injecting the second fluid down the wellbore under the second pressure is an injection phase of a cyclic steam stimulation hydrocarbon recovery process. 
     
     
         4 . The method of  claim 1  wherein the step of producing the hydrocarbon to the surface occurs through the wellbore. 
     
     
         5 . The method of  claim 1  further comprising drilling a second wellbore from the surface to the reservoir, wherein the step of producing the hydrocarbon to the surface occurs through the second wellbore. 
     
     
         6 . The method of  claim 1  wherein the step of injecting the first fluid down the wellbore under the first pressure is insufficient to compromise integrity of cap rock overlying the reservoir. 
     
     
         7 . The method of  claim 1  wherein the first fluid comprises steam, a steam-solvent mixture or a non-condensable gas. 
     
     
         8 . The method of  claim 1  wherein the second fluid comprises steam, a steam-solvent mixture or a non-condensable gas. 
     
     
         9 . The method of  claim 1  further comprising the step before step c. of heating the second fluid, wherein step d. comprises allowing heat to transfer from the second fluid to the hydrocarbon to mobilize the hydrocarbon. 
     
     
         10 . The method of  claim 1  wherein the first pressure is approximately 9500 kPa. 
     
     
         11 . The method of  claim 1  further comprising repeating steps b. through e. at least one time. 
     
     
         12 . The method of  claim 1  wherein an initial permeability of the subsurface reservoir is assessed before injecting the first fluid down the wellbore at the first pressure. 
     
     
         13 . The method of  claim 12  further comprising the step of determining a level for the first pressure sufficient to raise subsurface reservoir permeability above the initial permeability before injecting the first fluid down the wellbore at the first pressure. 
     
     
         14 . A method for recovering hydrocarbon from a subsurface reservoir, the method comprising the steps of:
 a. drilling a wellbore from surface to the reservoir;   b. injecting fluid down the wellbore under an initial pressure, the fluid at the initial pressure sufficient to substantially dilate at least a portion of the reservoir;   c. reducing pressure of the fluid to a reduced pressure and continuing to inject the fluid down the wellbore, the reduced pressure lower than the initial pressure and the fluid at the reduced pressure insufficient to substantially further dilate the at least a portion of the reservoir;   d. allowing the fluid to mobilize the hydrocarbon in the reservoir; and   e. producing the hydrocarbon to the surface.   
     
     
         15 . The method of  claim 14  wherein the step of injecting the fluid under the initial pressure is for a first period of time, and the step of injecting the fluid under the reduced pressure is for a second period of time, the first period of time being lesser than the second period of time. 
     
     
         16 . The method of  claim 14  wherein the step of injecting the fluid down the wellbore under the reduced pressure is an injection phase of a cyclic steam stimulation hydrocarbon recovery process. 
     
     
         17 . The method of  claim 14  wherein the step of producing the hydrocarbon to the surface occurs through the wellbore. 
     
     
         18 . The method of  claim 14  further comprising drilling a second wellbore from the surface to the reservoir, wherein the step of producing the hydrocarbon to the surface occurs through the second wellbore. 
     
     
         19 . The method of  claim 14  wherein the step of injecting the fluid down the wellbore under the initial pressure is insufficient to compromise integrity of cap rock overlying the reservoir. 
     
     
         20 . The method of  claim 14  wherein the fluid comprises steam, a steam-solvent mixture or a non-condensable gas. 
     
     
         21 . The method of  claim 14  further comprising the step before step c. of heating the fluid, wherein step d. comprises allowing heat to transfer from the fluid to the hydrocarbon to mobilize the hydrocarbon. 
     
     
         22 . The method of  claim 14  wherein the initial pressure is approximately 9500 kPa. 
     
     
         23 . The method of  claim 14  further comprising repeating steps b. through e. at least one time. 
     
     
         24 . The method of  claim 14  wherein an initial permeability of the subsurface reservoir is assessed before injecting the fluid down the wellbore at the initial pressure. 
     
     
         25 . The method of  claim 24  further comprising the step of determining a level for the initial pressure sufficient to raise subsurface reservoir permeability above the initial permeability before injecting the fluid down the wellbore at the initial pressure.