Alkaline Surfactant Flooding for Tight Carbonate Reservoirs

A laboratory study was undertaken to study the feasibility of oil recovery by surfactant flooding from an oil-wet carbonate reservoir. The unique features of the subject reservoir are its high salinity (and high divalent ion concentration) and low permeability (2–5 md). Alkali-surfactant combinations can be formulated which give low IFT (10−3 dynes/cm) at high salinity and hardness. Oil left after water flood can be mobilized by tertiary injection of low IFT surfactant formulations. Almost 95 % of the original oil was recovered in tertiary core floods using alkali-surfactant formulations. We could not identify a mobility control agent (polymer or foam) for such a low permeability rock. Thus slug surfactant processes were not attempted. A surfactant was identified which changed the wettability of oil-wet rocks to intermediate to slightly water-wet. 80% OOIP was recovered using the wettability altering surfactant in a secondary surfactant flood at 3 PVI in comparison to 60% from a waterflood at similar pressure drops.