Fractured Carbonates: A Methodology to Evaluate Surfactant Performances

Abstract

Abstract Wettability alteration is a key method for recovering oil from naturally-fractured, oil-wet carbonate reservoirs. Many surfactants have been proposed for this purpose, including sulfonates, alkyl ammonium bromides or ethoxylated alcohols. Nevertheless, the very intrinsic link between oil recovery from an initially oil-wet rock and surfactant characteristics has been poorly studied. In particular, the interplay between rock wettability alteration and oil/water interfacial tension (IFT) reduction due to chemicals is not fully described. We present a high throughput screening test to specifically address the problematic of surfactant effects on wettability. Automated contact angle measurements allow for the selection of successful candidates. From this screening, we propose a complete workflow using model minerals treated with crude oil and Amott/USBM measurements on outcrop carbonate cores. We demonstrate that taking into account surfactant effect both on IFT and on wettability gives superior results compared to focusing on aqueous solution spreading only. A qualitative correlation between results from high-throughput screening tests and Amott-Harvey wettability indexes variations is extracted. These results provide a consistent set of parameters to be included in future numerical simulations.