Physicochemical Interactions During Surfactant Flooding of Fractured Carbonate Reservoirs

TLDR

Poor waterflood recovery from fractured, oil‑wet/mixed‑wet carbonate reservoirs is a known problem. The study investigates how dilute alkaline anionic surfactant solutions interact with crude oil on carbonate mineral surfaces to improve oil recovery from fractured carbonates. Wettability, phase behavior, interfacial tension, and adsorption experiments were performed on carbonate surfaces with these surfactants. Anionic surfactants were shown to alter carbonate wettability to intermediate/water‑wet, reduce interfacial tension below 10⁻² mN/m, suppress adsorption with Na₂CO₃, and recover over 50 % of OOIP from oil‑wet cores in laboratory imbibition tests.

Abstract

Summary Recovery from fractured, oil-wet/mixed-wet, carbonate reservoirs by waterflooding is poor. Dilute surfactant methods are being developed to improve oil recovery from fractured carbonates. This paper investigates the interactions of dilute alkaline anionic surfactant solutions with crude oil on carbonate mineral surfaces. Wettability, phase behavior, interfacial tension, and adsorption experiments have been conducted. Anionic surfactants have been identified that can change the wettability of the calcite surface to intermediate/water-wet condition as well or better than the cationic surfactant dodecyl trimethyl ammonium bromide (DTAB) with a west Texas crude oil. All the carbonate surfaces (lithographic limestone, marble, dolomite, and calcite) show similar behavior with respect to wettability alteration with an anionic surfactant. Anionic surfactants, which lower the interfacial tension with the crude oil to very low values (<10−2 mN/m), have also been identified. The adsorption of the sulphonate surfactants can be suppressed significantly by the addition of Na2CO3, because the addition of carbonate can change the zeta potential of calcite to a negative value. Greater than 50% OOIP can be recovered from oil-wet carbonate cores by spontaneous imbibition of 0.05 wt% anionic surfactant solutions in the laboratory scale.