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. A hydrocarbon solvent having a density less than oil contained in the formation and a viscosity not greater than 1/100 the viscosity of the oil contained in the formation under formation conditions is injected into the communication path and fluids including oil are recovered from the production well until the fluid recovered contains an unfavorable ratio of oil to solvent. The production well is shut-in and an additional quantity of the hydrocarbon solvent is injected into the fluid communication path, preferably until a total amount of between 0.05 to 0.30 pore volume. The injection well is then shut-in along with the production well to permit the formation to undergo a soak period for a variable time, preferably for a time of between 2 to 20 days per vertical thickness in feet of oil-containing formation. A driving fluid such as water is then injected into the formation via the injection well and the oil is produced until there is an unfavorable ratio of oil to driving fluid. During the fluid drive recovery phase, the injection well and production well may be completed to be in fluid communication with the entire portion of the formation to obtain a more uniform displacement of the upgraded formation oil by the driving fluid.