Steam-channel-expanding steam foam drive

Claim 1

A process for recovering oil from a subterranean reservoir, comprising: injecting steam and producing fluid at horizontally spaced locations within a portion of a viscous oil reservoir in which the disposition of a steam flow path is determined by the effect of gravity and/or oil distribution, rather than being substantially confined within only one or a few most permeable layers of reservoir rocks; maintaining rates of steam injection and fluid production such that a steam breakthrough into a production location becomes at least substantially imminent and the extention of a steam channel from an injection location to a production location is at least substantially complete; changing the composition of the fluid being injected from steam to a steam-foam-forming mixture consisting essentially of steam, noncondensable gas and an aqueous electrolyte-containing solution or dispersion of surfactant; correlating the composition of the steam-foam-forming mixture with the properties of the rocks and fluids in the reservoir so that the pressure required to inject the mixture and the foam it forms or comprises into and through the steam channel exceeds that required for steam alone but is less than the reservoir fracturing pressure; and adjusting the composition of the fluid being injected into the steam channel to the extent required to maintain a flow of both steam and foam within the channel in response to a relatively high pressure gradient at which the oil-displacing and channel-expanding effects are significantly greater than those provided by steam alone, without plugging the channel.