A Comparative Enhanced Oil Recovery Study Between Low-Salinity Water and Hybrid Surfactant Process for a Carbonate Reservoir

Abstract

Abstract Over the years, water-based enhanced oil recovery (EOR) techniques have continuously been of interest for their superior technical and economic feasibility. Low-salinity water (LSW) flooding is an attractive EOR method as it can significantly improve the performance of the conventional waterflooding process all while being financially feasible at a reduced cost. Regardless of its widely acclaimed efficiency, its incapacity to substantially alter the fluid–fluid properties in the reservoir remains as one of the critical limitations of LSW flooding. The hybrid application of low-salinity water with surfactant (LSS) is a novel EOR approach with great efficiency in lowering oil-water interfacial tension (IFT) and altering the rock surface wettability. In this study, an extensive comparative analysis is held between LSW and LSS on a carbonate rock to evaluate the extent of the improvement achieved via the addition of the surfactant to the low-salinity water system. The experimental analysis between LSW and LSS is compiled based on the evaluation of fluid-fluid and rock-fluid interactions. The fluid-fluid interactions were assessed using IFT tests. The IFT between LSW and LSS solutions and crude oil was measured using the spinning drop tensiometer. The rock-fluid interactions were examined using zeta potential experiments, reservoir-condition HPHT coreflooding experiments in composite cores, and contact angle measurements in an exclusive and specifically-designed HPHT imbibition cell. The results of the IFT tests showed more effective oil-water interactions of the LSW when the surfactant was added to 1%diluted-seawater (1%dSW). IFT measurements of LSS solutions displayed significantly lower values which were substantially lower than LSW solution. The zeta potential experiments using the streaming potential method showed a clear trend of yielding more negative values for LSS solutions versus LSW at 1%dSW. The contact angle measurements confirmed a 17° difference for LSS when compared to LSW. These outcomes demonstrated that the wettability of the carbonate rock was altered from oil-wet to intermediate-wet with the addition of a low concentration of the surfactant. Coreflooding data proved conclusively that the addition of 0.2wt% of the surfactant to the LSW flooding yielded an additional 9.11% of oil recovery. The comprehensive experimental work followed in this study including contact angle and coreflooding data under HPHT conditions and zeta potentiometric studies on surface charges using whole brine-saturated cores make the findings more representative of field conditions. This paper is aimed to improve the understanding of the ability of a surfactant to improve the fluid-fluid interactions and alter the rock-fluid properties when added to LSW flooding.