Abstract: A viscoelastic foam system for an acidic gas switch improves the recovery factor. The viscoelastic foam system for an acidic gas switch has a pH-switch surfactant, a hydrocarbyl anionic surfactant and water. The pH-switch surfactant is at least one of long-chain hydrocarbyl amines. After the viscoelastic foam system meets the acidic gas, the interaction between the pH-switch surfactant and the hydrocarbyl anionic surfactant is enhanced, the viscosity increases, and the formed foam has better stability and plugging performance. When the viscoelastic foam system is injected at 1.0 PV, the apparent viscosity of the foam formed in the rock core is ?270 mPa·s, which can increase the recovery factor by more than 20%, and the long-chain hydrocarbyl amine improves the salt tolerance of the single anionic surfactant, so that the applicable mineralization range of the system is increased to 10-200 g/L.

Abstract: A method of extracting hydrocarbons from a subterranean formation includes injecting a surfactant composition into the subterranean formation and collecting hydrocarbons displaced by the injected surfactant composition. The surfactant composition can have at least one polyamine surfactant compound of formula R1R2NA(RNA)xNR3R4, where x is an integer from 0 to 3, R1, R2, R3, R4 and each R are independently a hydrogen atom or an alkyl group, each A is an alkylene group, and the total number of carbon atoms in the surfactant compound is from 10 to 21. The surfactant composition can include liquid or supercritical carbon dioxide.

Abstract: The invention relates to a method of extracting hydrocarbons from a subterranean formation, comprising: —injecting a surfactant composition into the subterranean formation, and —collecting hydrocarbons displaced by the injected surfactant composition; wherein the surfactant composition comprises at least one surfactant compound of formula (I): wherein x is an integer from 0 to 3, R1, R2, R3, R4 and each R are independently a hydrogen atom or an alkyl group, each A is an alkylene group, and the total number of carbon atoms in the surfactant compound of formula (I) is from 10 to 21. The invention also relates to a composition comprising liquid or supercritical carbon dioxide and at least one surfactant compound of formula (I).