Study on the Microscopic Migration Characteristics of CO2 Miscible Flooding Front Based on the Adsorption and Diffusion Mechanism

As a fossil energy, petroleum is widely used in industrial production and daily life. Currently, the exploration and development of oil is gradually moving toward unconventional reservoirs, and CO2 miscible flooding has a good oil displacement effect in low permeability reservoirs. At present, simulation studies on the microscopic migration characteristics of CO2 miscible flooding are mainly focused on laminar displacement, but the simulation of the migration change process of the CO2 front under adsorption and diffusion conditions is limited. In view of the above problems, a numerical model of miscible flooding is established, and the microscopic migration characteristics of the CO2 miscible flooding front under the conditions of adsorption and diffusion are simulated and analyzed through the coupling solution of multiple physical fields based on COMSOL at the two-dimensional pore scale. The research shows that CO2 first enters into large pores after being injected into pores and will diffuse to small pores. With increasing injection time, the CO2 concentration in the swept area gradually increases under the diffusion effect, and the adsorption concentration on the surface of the porous wall in the area with a higher concentration is also higher. The increase in the adsorption reaction rate constant will strengthen the adsorption of CO2 on the inner wall of the pores. The increase in the diffusion coefficient is beneficial for increasing the swept area. This study has guiding significance for the field to understand the microscopic migration characteristics of CO2 miscible flooding fronts under the action of adsorption and diffusion.