Oil Recovery From Fractured Carbonates by Surfactant-Aided Gravity Drainage:Laboratory Experiments and Mechanistic Simulations

摘要

Waterflooding recovers little oil from naturally fracturedcarbonate reservoirs if the matrix is oil-wet and fractureintensity is high. Laboratory experiments and mechanisticsimulations have been conducted to understand the injectionof dilute anionic surfactant solutions into oil-wet, fracturedreservoirs. In this process, surfactant diffuses into the matrix,lowers IFT and contact angle, which decrease capillarypressure and increase oil relative permeability enabling gravityto drain the oil up. The rate of oil recovery increases with anincrease in matrix permeability, a decrease in initial gassaturation, a decrease of fracture height or spacing, and anincrease in wettability altering capabilities of the surfactant.Increasing the surfactant concentration does not necessarilyenhance the oil recovery rate, because IFT and wettabilityalterations are not related to surfactant concentration linearly.Adsorption of anionic surfactants on calcite can be suppressedwith an increase in pH and a decrease in salinity.