Comparative Study on Numerical Simulation of CH4 Breakthrough Pressure in Unsaturated Rock Based on Step-By-Step Method and Continuous Injection Method

Gas breakthrough pressure is a key parameter affecting gas production and evaluation of tight reservoir sealing capabilities. This study aims to explore the impact of different injection methods on CH₄ breakthrough pressure in unsaturated rocks. COMSOL Multiphysics was used to simulate the CH₄ breakthrough process, and comparative analysis was conducted using step-by-step and continuous injection methods. The results show that the step-by-step method has higher measurement accuracy under low CH₄ breakthrough pressure and is suitable for scenarios that require precise evaluation, whereas the continuous injection method is more efficient under high CH₄ breakthrough pressure and is suitable for rapid evaluation needs. According to outcomes of simulation, this research suggested a numerical optimization framework aimed at forecasting the breakthrough pressure of CH₄ and verified the accuracy and applicability of the model through linear fitting of experimental data and predicted values. In addition, the study also conducted a sensitivity analysis on the pore distribution index (m) and injection flow rate (u_in) in the van Genuchten model. The results show that u_in has a small impact on breakthrough pressure, whereas m has a considerable effect on breakthrough pressure. An increase in m leads to an increase in breakthrough pressure, thereby enhancing the sealing performance of rock core. This study reveals the applicability difference between the step-by-step method and the continuous injection method in predicting CH₄ breakthrough pressure and proposes an effective prediction method based on numerical simulation, which provides valuable insights for selecting gas injection methods and predicting breakthrough pressure in rocks. © 2025 Society of Chemical Industry and John Wiley & Sons, Ltd.