The objective of this research was to develop a surfactant formulation for EOR in an oil-wet, high-salinity, fractured dolomite reservoir at ~100°C. A key requirement was achievement of interfacial tension (IFT) sufficiently low to spontaneously displace oil from the matrix by buoyancy. The formulation developed to do so was a blend of lauryl betaine and C15-18 internal olefin sulfonate, supplemented by a smaller amount of i-C13 ethoxylated carboxylate, all thermally stable and commercially available surfactants although the carboxylate not in quantities required for largescale EOR processes. Proportions of the three surfactants for injection in hard sea water were selected using equilibrium phase behavior results and estimates of IFT obtained by a novel technique based on the manner in which oil exits a small, vertically-oriented, rectangular oil-wet capillary cell as it is displaced upward in the cell by surfactant solution. The ability to recover oil from an oil-wet dolomite core was confirmed by an Amott imbibition cell experiment in which 50% recovery was observed for a core initially fully saturated with oil. The formulation's ability to generate strong foam in porous media was presented earlier in SPE-181732-MS. Research at Rice for three additional projects having carbonate reservoirs but different crude oils, brines, and temperatures of at least 60°C demonstrated formulation versatility by showing good oil recovery by core floods with modestly adjusted proportions of the same three surfactants (SPE-184569-MS, 2017; SPE-190259-MS 2018, US Patent 9,856,412). In the first two of these cited studies, the foamed formulation was injected to recover crude oils from a novel model fracture-matrix system.

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