A New Strategy to Minimize the Surfactant Adsorption on Saudi Carbonate

Surfactants play a vital role in chemical enhanced oil recovery (cEOR) to improve oil production by lowering the oil-water interfacial tension and/or altering the rock wettability. However, surfactant adsorption has been a great challenge. The quantity of surfactant loss by adsorption on a rock directly influences a cEOR project's economics. Therefore, surfactant adsorption minimization is an important area of interest, which is investigated in this paper. Saudi carbonate rock (outcrop) was tested with a novel in-house synthesized cationic Gemini surfactant to quantify surfactant adsorption. This novel surfactant is compatible with high salinity and high-temperature environment. Rock characterization was performed first using XRD and SEM analyses, while the point of zero charge of Saudi carbonate was found using the pH drift method. Static adsorption tests were conducted using powdered rock sample and run for 24 hours to achieve the equilibration time. The material balance method was used to determine surfactant adsorption. High-performance liquid chromatography along with an evaporative light scattering detector was utilized to quantify the remaining surfactant concentration post-adsorption. Adsorption isotherm modeling was also performed to investigate the adsorption mechanism. Rock characterization results showed that Saudi carbonate contains mainly dolomite along with some impurities like quartz and clay minerals. The point of zero charge of Saudi carbonate determined using the pH drift method was around 10. The static adsorption tests were conducted on both pure and Saudi dolomites to investigate the influence of impurities. It was found that the presence of quartz and clay particles significantly impacts the degree of surfactant adsorption on Saudi carbonates. A high adsorption of the novel Gemini surfactant used was obtained on Saudi carbonate (8.2 mg/g-rock). A powerful chelating agent made from natural, biodegradable, and renewable material was added to the surfactant solution to check its impact. The surfactant adsorption was significantly decreased using low pH chelating agent (5.8 mg/g-rock). It is proposed that low pH chelating agent renders the overall rock surface more positive and results in electrostatic repulsion between like charges of rock and surfactant. Therefore, the addition of a small quantity of the investigated chelating agent to the surfactant solution helps in reducing the cationic Gemini surfactant adsorption on Saudi carbonate. This study reports a novel strategy to minimize surfactant adsorption on Saudi carbonate through the use of an environmentally friendly and low-cost chelating agent, which will help in designing future chemical EOR projects.