Abstract: A method is disclosed for displacing hydrocarbon fluid within a subterranean formation by the introduction of an aqueous micellar fluid. In the method, the aqueous micellar fluid comprises a surfactant, from about 1 to about 30 wt. % sulfonate, and as the major constituent, water. The sulfonate further is comprised of a mixture of monosulfonate and disulfonate. At the start of the introduction of the aqueous micellar fluid, a monosulfonate-rich sulfonate mixture is utilized and at the end of the introduction, a disulfonate-rich mixture is utilized. Such grading or adjusting or mono- to disulfonates is used to increase the effectiveness of the micellar fluid and can occur throughout the introduction process either linearly or exponentially with respect to time, or in block slugs in the micellar fluid alone, a phase control fluid alone, or across both.

Abstract: An improved method of oil recovery for use within an underground formation having an ion exchange capacity. An aqueous micellar fluid bank containing a surfactant is injected into the formation followed by an injection of the bank with a mobility control fluid, such as a polymer-thickened aqueous solution, into the formation. The mobility control fluid has a salt level lower than or equal to the salt level of the micellar fluid, but a greater divalent cation-to-monovalent cation ratio than the micellar fluid make-up brine, preconditioning brine or original in-place brine in a reservoir in order to reduce the hardness of the formation fluids in situ generated at the trailing edge of the micellar fluid which in turn reduces the surfactant loss from the micellar fluid.