CYCLICAL STEAM FLOODING METHOD FOR VISCOUS OIL RECOVERY

CYCLICAL STEAM FLOODING METHOD FOR VISCOUS OIL RECOVERY ASTRACT Viscous oil is recovered from a subterranean, viscous oil containing, permeable formation, penetrated by at least one injection well and at least one spaced-apart production well in which a fluid communication path exists or in which a fluid communicaton path is first established between the wells. The method involves a cyclical pressurization-drawdown program in which initially steam is injected into the injection well at a predetermined rate and fluids including oil are produced from the production well at a restricted flow rate equal to a value 50 percent or less than the flow rate of the steam being injected into the injection well. Steam injection and restricted production is continued until the wellhead temperature of the fluids is within the range of 175 to 250.degree.F. Thereafter, the drawdown phase begins by increasing production to a maximum value and simultaneously reducing the injection rate of steam to a value about 20 percent of the original injection rate until the oil content in the produced fluids decreases to an unfavorable level. This sequence is repeated for a plurality of cycles until the desired oil recovery has been attained.