Steam injected into a subterranean formation comprises a liquid phase and a vapor phase. Oil displacement by the liquid phase is not as efficient as the oil displacement in the portion of the formation contacted by the vapor phase. The effectiveness of the oil recovery process in the portion of the formation being contacted by the liquid phase is increased by contacting that portion of the formation with an aqueous solution containing from 0.005 to 2.0 percent by weight of an alkalinity agent, preferably sodium hydroxide, and from 0.01 to 5.0 percent by weight of a buffering agent, preferably sodium carbonate. The mixture of sodium hydroxide and sodium carbonate may be co-mixed with the steam introduced into the formation, or may be introduced as a separate liquid containing both the sodium carbonate and sodium hydroxide, or separate slugs containing sodium carbonate and sodium hydroxide may be injected.

Heavy or viscous oils may be recovered from subterranean deposits by one or more wells each of which is provided with at least two separate communication means from the surface of the earth, one in fluid communication with the upper part of the formation and the other well being in fluid communication with the lower part of the formation, each of said communication means being completed so as to permit injection of steam or mixtures of steam and other materials into the formation and production of heated viscous petroleum therefrom. The oil recovery process comprises several separate phases of operation. In the first, steam is injected into the formation using both communication means simultaneously for a period of time followed by a soak period if desired, followed by production of heated oil from both parts of the formation using both communication means simultaneously. In the second phase, steam is injected into only one of the communication means, which may be the one in communication with either the top or bottom part of the formation, and oil production is taken from the other communication means. This is followed by a reversal of injection-production sequences, the process effectively pressure pulsing the formation to improve the distance into the formation that the push-pull steam injection process is effective.

The disclosed invention is a method for improving the permeability of an underground hydrocarbon reservoir containing clay particles or other silaceous fines where damage has occurred or may occur. The method requires the injection into the hydrocarbon reservoir of an aqueous treating solution having a pH greater than about 12 and comprising about 2% to about 25% by weight of an alkali metal hydroxide. The invention also includes the injection of an aqueous buffer solution into the reservoir before, and optionally, after the injection of the treating solution. The before and after buffer solutions should have a pH greater than about 12 and comprise about 0.5% to about 5% by weight of alkali metal hydroxide and about 0.5% to about 5% by weight of alkali metal salt. The high pH aqueous buffer solutions maintain reaction products in solution, minimizing precipitation within the formation from the treating solution.

A non-thermal, chemical "huff and puff" method for improved oil recovery is provided in which surfactant/cosurfactant/brine mixtures are used to recover viscous and other hydrocarbons from single wells.