Surfactant-flooding enhanced oil recovery - with drive fluid of controlled salinity to prevent partitioning of surfactant

摘要

In an enhanced oil recovery process employing injections of (a) a surfactant-contg. fluid (I) followed by (b) a polymer-contg. drive fluid (II) and (c) water having an unspecified salinity, the improvement comprises (i) determining the upper and lower salinity levels which the surfactant in (I) can tolerate, and (ii) controlling the salinity of (II) so as to prevent precipitation of surfactant from (I) and the irreversible partitioning of the surfactant from the aq. phase. Sp (II) contains as a first increment a quantity of fluid comprising water and an amt. of a hydrophilic polymer sufficient to raise the viscosity of the increment to an effective level, the volume of the increment ranges up from about 0.1 to about 1 pore volumes of the reservoir. The injected volume of (II) is sufficient to prevent breakthrough of the injected water of unspecified salinity inks (I). Any drive water which leaks through (II) into (I) will be at a controllable salinity level, maintaining efficient oil recovery levels.