An improved method for the recovery of heavy oils and bitumen from subterranean formations by the injection thereinto of a mixture of an oxygen-containing gas and steam in which the ratio of free oxygen in the gas to steam is in the range of 0.03 to 0.13 MSCF/bbl.

A method is disclosed for recovering hydrocarbons from heavy oil and tar sand formations by a series of sequenced steps, wherein the production wells are initially steam stimulated. Thereafter, about 0.6 to about 1.2 pore volumes of steam of a relatively high steam quality are injected into the formation through the injection wells. An additional quantity of steam is then injected wherein the steam quality is decreased to a relatively low quality. Water injection and wet in situ combustion conclude the method.

Solid hydrocarbon materials remaining in a subsurface earth formation such as, for example, the coke residue remaining in a subterranean tar sand deposit which has previously been exploited by means of a controlled oxidation process, is reignited and an oxygen-containing gas such as air is injected to burn the coke residue, thereby increasing the temperature of the sand or other formation matrix substantially. Water is then injected into the formation to absorb heat from the hot sand or formation matrix. Hot water and/or steam is thereby generated for use in thermal oil recovery methods in the immediate vicinity without the need for burning natural gas or other fuels which can be used more advantageously. Since the premeability of a tar sand formation is substantially greater at the conclusion of the controlled oxidaton reaction than it has initially, water containing appreciable solids suspended therein as well as minerals dissolved therein may be utilized without danger of plugging the formation, thus eliminating the cost of water treatment as would be required in conventional steam generation practice.

Viscous petroleum may be recovered from viscous petroleum-containing formations such as tar sand deposits in a process employing steam and air or a free oxygen-containing gas in the ratio of 0.05 to 0.65 M.S.C.F. per bbl. and a cyclical injection-production program in which first steam or steam and air are injected and fluids are produced without restriction until live steam is produced at the production well, after which steam and air are injected and production throttled to a value less than 50% and preferably less than 20% 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 air injection is reduced to a value less than 50% and preferably less than 20% of the original injection rate. The process should be applied to a formation in which adequate communication exists or in which a communication path is first established. The air and steam in the optimum ratio cause a low temperature, controlled-oxidation reaction in the formation. Optimum results are obtained if the pressurization and drawdown cycles are initiated shortly after the beginning of the steam-air injection program, and the process results in substantially increased oil recovery efficiency at all values of steam pore volumes injected.