Selective steam foam soak oil recovery process

Claim 1

In an oil recovery process in which steam mixed with steam-foam-forming components is injected into a substerranean reservoir that contains a heavy oil and is susceptible to gravity override and, after a soak period, fluid is backflowed for production from the reservoir, an improvement which comprises: mixing the steam injected into the reservoir with at least one each of noncondensible gas, monovalent cation salt and surfactant; arranging the chemical compositions and proportions of the components mixed with the steam relative to both the quality of the steam and the chemical composition of the reservoir oil so that the foam formed by the mixture is significantly chemically weakened by contact with the reservoir oil; and injecting the so-arranged mixture of steam and steam-foam-forming components and producing the fluid backflowed from the reservoir at rates and pressures such that the steam foam located within a zone of the reservoir in which the foam contacts a significant proportion of oil, tends to become chemically weakened and more mobile before the condensing of the steam from the gaseous component of the steam foam has become significant.