Method Of Injecting Solvent Into An Underground Reservoir To Aid Recovery Of Hydrocarbons

Abstract

Described is a method of operating a cyclic solvent-dominated recovery process (CSDRP) for recovering viscous oil from a subterranean reservoir of the viscous oil. The cyclic solvent process involves using an injection well to inject a viscosity-reducing solvent into a subterranean viscous oil reservoir. Reduced viscosity oil is produced to the surface using the same well used to inject solvent. The process of alternately injecting solvent and producing a solvent/viscous oil blend through the same wellbore continues in a series of cycles until additional cycles are no longer economical. To improve solvent efficiency, the injection includes at least one restriction duration, where injection is restricted, between two continuous injection periods.

1 . A method of controlling a cyclic solvent injection and production process to aid recovery of hydrocarbons from an underground reservoir, the method comprising:
 (a) injecting a volume of fluid comprising greater than 50 mass % of a viscosity-reducing solvent into an injection well completed in the reservoir;   (b) halting injection into the injection well and subsequently producing at least a fraction of the injected fluid and the hydrocarbons from the reservoir through a production well;   (c) halting production through the production well; and   (d) subsequently repeating the cycle of steps (a) to (c);   wherein step (a) comprises at least one restriction duration, where injection is restricted, between two continuous injection periods, for improving solvent efficiency.   
     
     
         2 . The method of  claim 1 , wherein the at least one restriction duration is for a longer time than at least one of the two continuous injection periods. 
     
     
         3 . The method of  claim 1 , wherein the at least one restriction duration is for a predetermined duration of time greater than 4 hours. 
     
     
         4 . The method of  claim 1 , wherein the at least one restriction duration is for at least twice as long a time as at least one of the two continuous injection periods. 
     
     
         5 . The method of  claim 1 , wherein at least one of the two continuous injection periods are predetermined periods of time greater than 4 hours. 
     
     
         6 . The method of  claim 1 , wherein a peak injection rate during at least one of the two continuous injection periods is at least 4 times greater than an average injection rate during the at least one restriction duration. 
     
     
         7 . The method of  claim 1 , wherein a peak injection rate during at least one of the two continuous injection periods is at least 10 times greater than an average injection rate during the at least one restriction duration. 
     
     
         8 . The method of  claim 1 , wherein a peak injection rate during at least one of the two continuous injection periods is at least 100 times greater than an average injection rate during the at least one restriction duration. 
     
     
         9 . The method of  claim 1 , wherein an average injection rate during at least one of the two continuous injection periods is at least 4 times greater than an average injection rate during the at least one restriction duration. 
     
     
         10 . The method of  claim 1 , wherein an average injection rate during at least one of the two continuous injection periods is at least 10 times greater than an average injection rate during the at least one restriction duration. 
     
     
         11 . The method of  claim 1 , wherein an average injection rate during at least one of the two continuous injection periods is at least 100 times greater than an average injection rate during the at least one restriction duration. 
     
     
         12 . The method of  claim 1 , wherein a volume of solvent injected during the at least one restriction duration is 0-25% of a volume of solvent injected during at least one of the two continuous injection periods. 
     
     
         13 . The method of  claim 1 , wherein step (a) comprises alternating between continuous injection periods and restriction durations. 
     
     
         14 . The method of  claim 1 , wherein the at least one restriction duration comprises ceasing injection. 
     
     
         15 . The method of  claim 1 , wherein, in at least one cycle, an in situ volume of fluid injected in steps (a) to (c) is equal to a net in situ volume of fluids produced from the production well in an immediately preceding cycle plus an additional volume of fluid. 
     
     
         16 . The method of  claim 1 , wherein at least one of the two continuous injection periods is for a predetermined period of time after an estimated bottomhole pressure reaches a primary threshold pressure. 
     
     
         17 . The method of  claim 1 , wherein the at least one restriction duration is for a predetermined duration of time after an estimated bottomhole pressure reaches a secondary threshold pressure. 
     
     
         18 . The method of  claim 1 , wherein at least one restriction duration is determined by a time required to inject a predetermined volume of fluid after an estimated bottomhole pressure reaches a secondary threshold pressure. 
     
     
         19 . The method of  claim 1 , wherein at least one of the two continuous injection periods is determined by a time required to inject a predetermined volume of fluid after an estimated bottomhole pressure reaches a primary threshold pressure. 
     
     
         20 . The method of  claim 1 , wherein at least one of the two continuous injection periods is determined by a time required to inject a predetermined volume of fluid after an injection rate reaches a target injection rate. 
     
     
         21 . The method of  claim 1 , wherein the at least one restriction duration is 1 to 9 restriction durations. 
     
     
         22 . The method of  claim 1 , wherein one or each of the two continuous injection periods is greater than 1 hour and less than 10 days. 
     
     
         23 . The method of  claim 1 , wherein one or each of the two continuous injection periods is greater than 6 hours and less than 72 hours. 
     
     
         24 . The method of  claim 1 , wherein the at least one restriction duration is greater than 1 hour and less than 10 days. 
     
     
         25 . The method of  claim 1 , wherein the at least one restriction duration is greater than 6 hours and less than 72 hours. 
     
     
         26 . The method of  claim 1 , wherein a duration of time for the at least one restriction duration is determined by a time required for an estimated bottomhole pressure to drop to a secondary threshold pressure. 
     
     
         27 . The method of  claim 1 , wherein an injection pressure during the at least one restriction duration is equal to a secondary threshold pressure above an initial reservoir pressure. 
     
     
         28 . The method of  claim 1 , wherein the method is operated using a plurality of wells, each undergoing the cycles of injection and production according to substantially the same schedule. 
     
     
         29 . The method of  claim 1 , wherein the injection well and the production well utilize a common wellbore. 
     
     
         30 . The method of  claim 1 , wherein the hydrocarbons are a viscous oil having a viscosity of at least 10 cP at initial reservoir conditions. 
     
     
         31 . The method of  claim 1 , wherein the solvent comprises, ethane, propane, butane, pentane, carbon dioxide, or a combination thereof. 
     
     
         32 . The method of  claim 1 , wherein the injected fluid comprises diesel, viscous oil, natural gas, bitumen, diluent, C 5+  hydrocarbons, ketones, alcohols, non-condensable gas, water, biodegradable solid particles, salt, water soluble solid particles, solvent soluble solid particles, or a combination thereof. 
     
     
         33 . The method of  claim 1 , wherein the injected fluid comprises at least 25 mass % liquid at the end of an injection cycle. 
     
     
         34 . The method of  claim 1 , wherein the injected fluid comprises less than 50 mass % solid at the end of an injection cycle. 
     
     
         35 . The method of  claim 1 , wherein at least 75 mass % of fluid injected in a solid phase transitions to a liquid phase by the end of a subsequent production cycle. 
     
     
         36 . The method of  claim 1 , wherein the at least 75 mass % of fluid injected in a solid phase dissolves into a liquid phase by the end of a subsequent production cycle. 
     
     
         37 . The method of  claim 1 , wherein during an injection cycle, the phase of the injected fluid entering the reservoir transitions from greater than 75 mass % in the vapor phase to greater than 75 mass % in the liquid phase. 
     
     
         38 . The method of  claim 1 , wherein during an injection cycle, the phase of the injected fluid entering the reservoir alternates between greater than 75 mass % in the vapor phase to greater than 75 mass % in the liquid phase. 
     
     
         39 . The method of  claim 1 , wherein the injected fluid is heated such that it is injected into the underground reservoir at a temperature greater than 20° C. 
     
     
         40 . The method of  claim 1 , wherein at least 25 mass % of the solvent in an injection cycle enters the reservoir as a liquid. 
     
     
         41 . The method of  claim 1 , wherein at least 25 mass % of the solvent at the end of an injection cycle is a liquid. 
     
     
         42 . The method of  claim 1 , wherein an in situ volume of fluid injected over a cycle is equal to a net in situ volume of fluids produced from the production well summed over all preceding cycles plus an additional in situ volume of fluid. 
     
     
         43 . The method of  claim 42 , wherein the additional in situ volume of fluid is, at reservoir conditions, equal to 2% to 15% of a pore volume within the reservoir zone around the injection well within which solvent fingers are expected to travel during the cycle. 
     
     
         44 . The method of  claim 1 , wherein the injected fluid comprises a diesel, viscous oil, bitumen, or diluent to increase the viscosity of the injected fluid.