The Impact of Displacement Patterns on CO₂ Storage in Saline Aquifers Based on Two Real Core Micromodels

Due to its widespread geological distribution and substantial storage capacity, CO₂ storage in saline aquifers is internationally recognized as one of the most effective methods for mitigating the greenhouse effect. The characteristics of the two-phase flow in porous media significantly affect the capacity and safety of CO₂ storage. In this study, two structures at different locations of the Berea core were obtained and subsequently etched into two different micromodels to investigate the two-phase flow characteristics between CO₂ and water. Using a microscopic visualization method, many experimental results have been obtained under different displacement patterns, including qualitative results of the displacement process, interface changes, and phase distributions and quantitative results of differential pressure, CO₂ relative permeability, fractal dimension, and CO₂ saturation. The results indicated that the maximum CO₂ saturation, relative permeability, and fractal dimension were achieved when the displacement pattern was viscous fingering with CO₂ predominantly existing in the micromodel as the main displacing channel. On the contrary, when the displacement pattern was capillary fingering, CO₂ clusters showed the characteristics of large numbers and small areas, which led to the minimum CO₂ saturation, relative permeability, and fractal dimension. Due to the simultaneous dominance of viscous and capillary forces, the flow characteristics under crossover fell between viscous fingering and capillary fingering, rendering them more complex. The phase states of CO₂ and water exerted a profound influence on the differential pressure and displacement processes, primarily driven by the viscosity ratio at varying temperatures and pressures. The influence of the micromodel structure on the displacement process was mainly reflected in the local two-phase flow dynamics, resulting in numerical variations without significantly altering the general trend of change.