Oil is recovered from an oil-bearing reservoir in a process employing an in-situ combustion process utilizing a combustion-supporting gas containing at least 75% by volume pure oxygen, and preferably substantially pure oxygen, and a sequence in which the production well or wells are cyclically throttled. In place of using an in-situ combustion process, mixtures of steam and carbon dioxide or mixtures of steam and low molecular weight C.sub.3 -C.sub.8 hydrocarbons are injected into the reservoir and the production well is cyclically throttled. The production well flow rate is restricted until the bottom-hole pressure of the well has increased to an amount of about 30% to about 90% of the fluid injection pressure at the injection well. Thereafter, the production well is opened and oil is recovered therefrom as the bottom-hole pressure declines. The throttled production cycle may be repeated at appropriate intervals during the process.

A method for the recovery of viscous oil from subterranean formations including tar sands by the injection of a mixture of carbon dioxide and steam into the formation through an injection well, after which formation fluids are recovered from the well in a cyclic manner, using the well alternately for injection and production. Incremental recovery is optimized by maintaining the ratio of carbon dioxide to steam within the range 200 to 300, preferably 230 to 270 SCF carbon dioxide per barrel of steam (with water equivalent) in the injected mixture.

A method of inhibiting the dissolution of the gravel pack and/or the erosion of silicate-containing formations subjected to steam-enhanced oil recovery processes. The method includes the addition of CO.sub.2 into the residual liquid phase of the steam, prior to injection down the well bore, to reduce the pH to form about pH 5 to about pH 9.

A method of recovering hydrocarbons from a reservoir under an active waterflood or water drive by injecting a recovery fluid comprising carbon dioxide or nitrogen under immiscible conditions, allowing the recovery fluid to soak, and producing the recovery fluid and formation fluids under conditionally miscible or miscible conditions after pressure has sufficiently increased in the wellbore area.

The invention comprises injecting about 5% to about 25% pore volumes of a recovery fluid simultaneously into an underground formation through at least two wells. One well which is destined to be the production well is shut-in for a soak period of about one to about 60 days while injection of the recovery fluid is continued through the second well. The shut-in well is then converted to a production well and hydrocarbons and other fluids are produced from the production well while recovery fluid is injected through the second well. The shut-in well is then converted to a production well and hydrocarbons and other fluids are produced from the production well while recovery fluid is injected through the second well.