Wettability alteration in carbonates: Low-cost ammonium surfactants based on bio-derivatives from the coconut palm as active chemicals to change the wettability form oil-wet to water-wet conditions

Fractured oil-wet carbonate reservoirs are often located at low temperatures and pressures, and the oil recovery by pure pressure depletion is usually low. The potential for improved oil recovery (IOR) is therefore very high. An IOR method is to change the wettability of the reservoir towards more water-wet conditions so that water can spontaneously imbibe into the matrix blocks and expel the oil. This paper focuses on cheap commercial available surfactants of the type R-N(CH3)3Cl prepared from fatty acids from the coconut palm, which are able to turn the carbonate water-wet when added to the injection water. Two products were tested: Arquad MC-50 (Arquad) containing a mixture with R=C12 and C14, and Dodigen 5462 (Dodigen) with the composition R=C12, C14, C16, and C18. Imbibition experiments using low-permeability (3 mD) outcrop chalk cores and 100–350 mD dolomite reservoir cores at 40 and 70 °C were performed, both with and without initial water. In general, Arquad was more efficient than Dodigen regarding imbibition rate. Very high oil recovery was obtained, approximately 70% of original oil in place (OOIP) for the chalk cores and ≈90% of OOIP for the dolomite cores. The imbibition mechanism is discussed in relation to the influence of capillary and gravity forces, and the difference in behavior of the two surfactant systems is discussed in terms of critical micelle concentration (CMC) and oil–water interfacial tension (IFT).