Chemical EOR Formulation for a Clay-Rich Sandstone Reservoir with Reduced Surfactant Consumption.

Alkali-surfactant-polymer (ASP) flooding can reduce oil-water interfacial tension to ultralow values and mobilize oil in petroleum reservoirs. Surfactant is consumed by adsorption/retention which is significant in clay-rich reservoirs. Alkali can be added to surfactant-polymer formulations to minimize surfactant adsorption. The goal of this work is to study the effect of alkali and surfactant concentrations on surfactant-brine-oil phase behavior and minimize the amount of surfactant and alkali while mobilizing oil in a clay-rich sandstone reservoir (at a temperature of 75 °C). Many surfactants were studied for ASP formulations, and a mixture of two surfactants was identified that can produce ultralow IFT (∼0.001 mN/m) with the oil at low surfactant concentrations. Ten different ultralow IFT formulations were identified, but only two formulations were evaluated for oil recovery and surfactant retention in core floods. The optimal salinity decreased when the surfactant concentration was reduced. The cumulative oil recovery was high (>94%) for three types of cores (Berea sandstone, Leopard sandstone, and a reservoir core). The surfactant retention was in the range of 0.11-0.22 mg/g of rock for high clay content (>8%) cores due to the presence of alkali. Decreasing the surfactant concentration (while keeping the total amount of surfactant the same) did not change the surfactant adsorption or oil recovery but delayed the oil production.