Viscous oil recovery method

Abstract

Viscous petroleum may be recovered from formations in a process employing steam and a light hydrocarbon, and a cyclical injection-production program comprising repetitive cycles, each comprising three steps. First steam or steam and hydrocarbons are injected and liquids are recovered from the formation without restriction so long as no vapor phase steam production occurs. Next, steam and hydrocarbons are injected and production throttled until the formation pressure at the production well rises to a value between about 60% to 95% of the steam injection pressure, after which fluid production is permitted without restriction and steam and hydrocarbon injection rate is reduced to 50% or less of the original injection rate. The process should be applied to a formation in which adequate communication exists. Suitable hydrocarbons include C.sub.3 through C.sub.12 paraffinic or olefinic hydrocarbons including natural mixture such as naphtha, natural gasoline, etc. Optimum results are obtained if the pressurization and drawdown cycles are initiated shortly after the beginning of the steam-hydrocarbon injection program, and the benefits include substantially increased oil recovery efficiency at all values of steam pore volumes injected, reduced pressure differential, reduced plugging of the communication channel, and production of a preponderance of the viscous petroleum in the form of an oil-in-water emulsion which is easier to handle and to resolve into relatively water-free oil than a water-in-oil emulsion.