关键词: 碳酸盐岩, 扩散系数, 多组分, 扩散实验, 数学模型

Abstract:

Currently, the international geopolitical landscape is complex and volatile, with energy supply chains facing significant uncertainties. Gas storage, as a crucial component of the national energy reserve system, can effectively mitigate risks from fluctuations in international natural gas market prices and supply disruptions, ensuring stable gas supply for residential and industrial use, thereby serving as a robust safeguard for national energy security. For the safe and efficient operation of gas storage under multi-component, multi-cycle injection, and production conditions, accurately understanding the diffusion and flow patterns of mixed gases—working gas and cushion gas—in gas storage is essential. However, experimental studies on gas diffusion mainly focus on shale, coal, and tight formations, leaving the diffusion patterns of multi-component gases in carbonate reservoirs poorly understood. In this study, carbonate rock samples from the Upper Carboniferous Huanglong Formation (upper member) of the Wolonghe gasfield were examined, and the distribution of pore-throat radius were characterized using nuclear magnetic resonance and high-pressure mercury intrusion experiments. Diffusion experiments were conducted on gas mixtures containing CH₄ with CO₂, N₂, and O₂. Through comparative analysis of fitting results, the optimal mathematical model for gas diffusion coefficients applicable to multiscale carbonate reservoirs was selected. The results showed that the carbonate rock samples exhibited pronounced distribution characteristics of multi-scale pore structure. Under identical temperature and pressure conditions, higher porosity and permeability led to larger diffusion coefficients for all gas components. Moreover, the binary diffusion coefficient of the CH₄-CO₂ pair exceeded that of the N₂-CO₂ pair. In a multi-component system, O₂ exhibited the largest diffusion coefficient, followed by CH₄, while N₂ and CO₂ had the smallest diffusion coefficients. The presence of O₂ affected how the diffusion coefficients of CH₄ and N₂ responded to changes in the volumetric fractions of CO₂ and N₂. The mathematical model optimized using experimental data can be extended to predict diffusion coefficients under different temperature and pressure conditions. These findings provide experimental and computational methods for accurately predicting the patterns of gas storage operations and designing rational operational strategies.

Key words: carbonate rock, diffusion coefficient, multi-component, diffusion experiment, mathematical model