System and Method for Enhanced Oil Recovery from Combustion Overhead Gravity Drainage Processes

Abstract

A pre-ignition heat cycle (PIHC) using cyclic steam injection and steam flood techniques is described that improves the recovery of viscous hydrocarbons from a subterranean reservoir using an overhead in-situ combustion technique such as combustion overhead gravity drainage (COGD). The PIHC, by developing horizontal and vertical transmissive zones, predisposes a viscous oil reservoir to develop a conformable combustion chamber. Good conformance of the combustion chamber enhances recovery factor and improves well operations in the field for in-situ combustion applications.

1 . A method of preparing an oil bearing reservoir for in-situ overhead combustion by developing transmissive pathways in the reservoir prior to igniting the reservoir, wherein the reservoir includes a reservoir well network having one or more injection wells and one or more vent wells located in the top portion of the reservoir and a horizontal drain located in the bottom portion of the reservoir, wherein the method comprises the steps of:
 injecting steam into one or more injection wells while imposing a pressure drawdown on the one or more vent wells;   injecting steam into the one or more vent wells while imposing a pressure drawdown on the one or more injection wells; and,   providing for cyclic reversal of steam injection and a pressure drawdown between the one or more vent wells and the one or more injection wells until a lateral transmissive zone is established in the top portion of the reservoir between the one or more injection wells and the one or more vent wells.   
     
     
         2 . The method as in  claim 1  further comprising the steps of:
 circulating steam into the horizontal drain to increase oil mobility in the region of the reservoir around the horizontal drain; and 
 injecting steam into the one or more injection wells while shutting in the one or more vent wells and evacuating fluids from said horizontal drain until a vertical transmissive zone is established between the one or injection wells and the horizontal drain. 
 
     
     
         3 . The method as in  claim 1  wherein the steam is injected at a rate that yields a circulating pressure in the reservoir below fracture pressure. 
     
     
         4 . The method as in  claim 1  wherein steam is injected at a rate that yields a circulating pressure in the reservoir exceeding fracture pressure. 
     
     
         5 . The method as in  claim 1  wherein the conformance of the transmissive zones is adjusted by control of injection and drawdown pressures during each step. 
     
     
         6 . The method as in  claim 1  wherein the reservoir is configured with two or more injection wells over the horizontal drain and two or more laterally displaced vent wells. 
     
     
         7 . The method as in  claim 1  wherein after ignition, the lateral transmissive zones enable the combustion chamber to expand laterally through the lateral transmissive zones. 
     
     
         8 . The method as in  claim 1  wherein progression of the lateral transmissive zones is indirectly monitored from temperature data obtained from one or more observation wells in contact with the reservoir. 
     
     
         9 . The method as in  claim 1  wherein progression of the lateral transmissive zones is monitored from pressure communication data derived from pressure readings between the one or more injection wells and the one or more vent wells. 
     
     
         10 . The method as in  claim 2  wherein progression of the vertical transmissive zone is monitored from pressure communication data derived from pressure readings between the one or more injection wells and the horizontal well. 
     
     
         11 . The method as in  claim 1  further comprising the step of monitoring temperature data from the reservoir from one or more observation wells adjacent the one or more injection wells. 
     
     
         12 . The method as in  claim 2  wherein the steam is injected at a rate that yields a circulating pressure in the reservoir below fracture pressure. 
     
     
         13 . The method as in  claim 2  wherein steam is injected at a rate that yields a circulating pressure in the reservoir exceeding fracture pressure. 
     
     
         14 . The method as in  claim 12  wherein the conformance of the transmissive zones is adjusted by control of injection and drawdown pressures during each step. 
     
     
         15 . The method as in  claim 14  wherein the reservoir is configured with two or more injection wells over the horizontal drain and two or more laterally displaced vent wells. 
     
     
         16 . The method as in  claim 15  wherein after ignition, the lateral transmissive zones enable the combustion chamber to expand laterally through the lateral transmissive zones. 
     
     
         17 . The method as in  claim 16  wherein progression of the lateral transmissive zones is indirectly monitored from temperature data obtained from one or more observation wells in contact with the reservoir. 
     
     
         18 . The method as in  claim 17  wherein progression of the lateral transmissive zones is monitored from pressure communication data derived from pressure readings between the one or more injection wells and the one or more vent wells. 
     
     
         19 . The method as in  claim 18  wherein progression of the vertical transmissive zone is monitored from pressure communication data derived from pressure readings between the one or more injection wells and the horizontal well. 
     
     
         20 . The method as in  claim 19  further comprising the step of monitoring temperature data from the reservoir from one or more observation wells adjacent the one or more injection wells.