Novel WAG Method with Nanotechnology in a Heterogeneous Carbonate Reservoir

Abstract

Abstract In the WAG process, adding nanoparticles to the water phase (referred to as NWAG) is a method advantageous for enhancing oil recovery and CO2 storage by improving wettability. Previous research had limitations in not reflecting actual site conditions, as it did not account for heterogeneity and hysteresis. However, most reservoirs exhibit different permeability distributions, and CO2 can be trapped due to hysteresis. Therefore, it is essential to consider petrophysical properties, such as heterogeneity and relative permeability hysteresis, for accurate predictions. In this study, a 3-D heterogeneous reservoir model with a relative permeability hysteresis model was designed. Based on this model, a sensitivity analysis of the NWAG method was conducted for each factor to investigate its impact on oil recovery and CO2 storage. This analysis was performed using the CMG-GEM simulator, and the results were compared with the findings obtained for each different factor. A Dykstra-Parson coefficient of 0.4 was selected to represent the reservoir's heterogeneity. Furthermore, the capillary trapping of CO2 during WAG injection was calculated using Larsen and Skauge's three-phase relative permeability hysteresis model. The sensitivity analysis considered factors such as injection fluid-gas ratio, slug size, injection period, injection cycle, and nanofluid concentration. The simulation results indicated that the heterogeneity and hysteresis model have an impact on oil recovery and CO2 storage. Specifically, when considering both heterogeneity and hysteresis, oil recovery and CO2 storage exhibited differences of 0.8% each. In the simulation model that incorporated heterogeneity and hysteresis, the difference in oil recovery was 0.8%, while the difference in CO2 storage was 15.2%. Comparing nanofluid injection to CO2-WAG, it was observed that nanofluid injection can alter wettability by reducing permeability. This mechanism suggests that the use of nanofluids can enhance oil recovery and expand CO2 storage, resulting in an efficiency improvement of up to 5% in both oil production and CO2 storage when compared to the conventional WAG process. The NWAG method can offer new insights into the highly effective exploitation of oil reservoirs. Considering a limited supply of CO2 from industry and a constant source, the NWAG method is expected to be efficient way to enhance oil recovery and increase CO2 storage capacity.