Method of solvent flooding to recover viscous oils

Abstract

Oil may be recovered from viscous oil-containing formations including tar sand deposits by first establishing a fluid communication path in the lower portion of the formation intermediate at least one injection well and a production well. At least one additional interior production well in fluid communication with the upper portion of the formation is drilled within the formation defined by the injection well and production well. A hydrocarbon solvent having a density less than oil contained in the formation under formation conditions is injected into the fluid communication path via an injection well and fluids including oil are recovered from the production well until solvent is detected in the fluid recovered. Thereafter, the production well is shut-in and the interior production well is opened to production for recovering fluid including oil while solvent is continued to be injected into the fluid communication path via the injection well until the fluid recovered from the interior production well contains a predetermined amount of solvent. The injection well, production well, and interior production well are shut-in to permit the formation to undergo a soak period for a variable time, preferably from 1 to 10 days per vertical thickness in feet of the viscous oil-containing formation. Thereafter, a driving fluid such as water is injected into the formation and oil is produced via the production well until there is an unfavorable ratio of oil to driving fluid.