Study on the free motion mechanism and influencing factors of acidic gas in porous media

The application of conventional acidification techniques confronts significant challenges in ultra-low porosity reservoirs. To resolve this issue, it is essential to develop an alternative acidification method. The present research utilized high-temperature and high-pressure experiments and molecular dynamics simulations to develop a three-dimensional model that describes acid gas diffusion behavior. The model quantifies the diffusion coefficient of acid gases within tight sandstone and analyzes the influence of various parameters such as pore tortuosity, pore geometry, and variations in temperature and pressure conditions on this process. Moreover, diffusion kinetics are explored through mean square displacement analysis, revealing the free diffusion mechanism of acid gas in tight rock porous media. Empirical results indicate that carbon dioxide (CO2) demonstrates the highest molecular diffusion. Meanwhile, simulations show that the combined hydrogen fluoride (HF) and CO2 molecules have the greatest diffusion coefficient. Experimental values were lower than those predicted by simulations. This deviation may be attributed to high tortuosity and complex flow around the core pores compared to the simplified structures used in simulations. The simulation results reveal that the pore tortuosity is the dominant factor influencing diffusion, while the impact of pore diameter effect is relatively negligible.