Investigation of Gas Diffusion Time Dynamics at the Bottom Hole Under Convection–Diffusion Coupling Mechanisms

Abstract

In the study of underground gas diffusion, traditional methods often emphasize diffusion while neglecting the potential impact of convection. This research constructs a coupled model of diffusion and convection to investigate gas transmission characteristics in complex underground environments. The model is validated and calibrated using field measurement data. The results indicate that the coupled model provides a more accurate representation of gas concentration distribution and diffusion time compared to models that consider only diffusion. Furthermore, this study examines the influence of horizontal well inclination angle on gas diffusion time within the framework of convection–diffusion coupling, revealing its underlying variation patterns. This analysis offers a theoretical foundation for enhancing efficiency and safety in oil and gas production as well as related operations. Under the convection–diffusion coupling mechanism, it is found that the inclination angle of horizontal wells significantly affects gas diffusion time; specifically, larger inclination angles result in shorter durations for gas to diffuse from the bottom to the wellhead. Understanding these variation patterns can facilitate optimization in horizontal well design, rational arrangement of production processes, precise prediction of diffusion times, enhancement of existing safety measures, and provision of forward-looking methodologies and technical support for addressing potential risk events within the oil and gas industry. This has substantial practical implications for engineering applications.