Evaluation of Co2 flooding assisted by silica nanoparticles : study of oil recovery mechanisms and efficiency through experiments and simulation

Abstract

Oil production is commonly divided into primary, secondary, and tertiary recovery stages. Although primary and secondary recovery methods can produce a substantial portion of the original oil in place, a significant amount of oil remains trapped in the reservoir due to capillary forces and inefficient displacement. Enhanced Oil Recovery (EOR) techniques are therefore applied to improve oil recovery beyond conventional production methods. Among the available EOR techniques, CO2 flooding has been widely recognized for its ability to improve oil displacement efficiency. However, limitations related to sweep efficiency and fluid mobility may reduce its overall effectiveness. Silica nanoparticles have emerged as a promising additive to CO2 flooding due to their potential to modify rock-fluid interactions and improve displacement performance. This study was conducted to evaluate the oil recovery mechanisms associated with CO2 flooding assisted silica nanoparticle and to identify effective injection strategies under reservoir conditions and immiscibility conditions. A combination of micromodel experiments, coreflooding tests, SEM-EDS analysis, ICP-OES analysis, interfacial tension measurements, contact angle measurements, and numerical simulation was employed to investigate the interactions between nanoparticles, reservoir rock, and fluids. The integration of these experimental and simulation approaches provided a comprehensive assessment of the performance of CO2 flooding assisted silica nanoparticle. The results demonstrated that CO2 alternating nanoparticle flooding was the optimum injection strategy among the investigated injection schemes which achieved the highest recovery factor of approximately 92% in the micromodel experiments. The addition of silica nanoparticles enhanced the effectiveness of CO2 flooding through multiple recovery mechanisms. The recovery factor increased from 81.2% to 88.6%, corresponding to an additional 7.4 percentage compared to conventional CO2 alternating brine flooding. History matching indicated a significant increase in the optimized water Corey exponent (Nw) from 1.30 to 2.62, suggesting a change in the relative permeability characteristics of the rock. This observation is consistent with the wettability alteration, where silica nanoparticle adsorption modified the rock surface toward a more water-wet condition. Furthermore, the contact angle decreased from 47.0° to 45.7°, indicating a slight wettability alteration toward a more water-wet condition. These observations were supported by SEM-EDS and numerical simulation, which collectively confirmed nanoparticle retention, rock–fluid interactions, and improved displacement efficiency. Consequently, the injected CO2 can desorb attached oil through the mechanisms under immiscibility conditions including oil swelling and viscosity reduction. Overall, the findings demonstrate that CO2 flooding assisted silica nanoparticle has strong potential as an effective EOR technique and provides valuable insight into the mechanisms responsible for enhanced oil recovery.