CO₂ Diffusion and Water Barrier Rupture in Water-Shielded Blind-Ending Pores

The water barrier in blind-ending pores hinders direct contact between injected CO2 and residual oil, thereby limiting the effectiveness of tertiary CO2 flooding. Understanding the dynamics of CO2 diffusion and water barrier rupture in blind-ending pores is essential for optimizing recovery strategies. This study investigates the physical process of CO2 diffusion and water barrier rupture in blind-ending pores and preliminarily explores the potential of solvent-assisted CO2 flooding to accelerate water barrier rupture. First, the mathematical models at different stages are developed based on the differences in the diffusion system. Then, the corresponding numerical models are established and coded. The accuracy of the model is validated by comparing simulation results to experimental results obtained from reported studies. The simulation results indicate that water barrier rupture in blind-ending pores occurs in two stages: CO2 penetrating the water barrier, followed by oil swelling and water barrier rupture. In addition, we establish a generalized model for predicting the rupture time of the water barrier (tR) based on the alternating conditional expectation algorithm. Subsequent sensitivity analysis indicates that the CO2 diffusion coefficient in the water barrier is a key parameter affecting tR. Finally, a series of CO2 mass transfer experiments are conducted in a PVT cell. The experimental results indicate that tR is reduced by 17.7% with the introduction of an optimal solvent concentration of 1 wt %. This study may provide some new insights into the CO2 diffusion and water barrier rupture in water-shielded blind-ending pores.