我国煤层地质构造复杂、围岩应力高、含水率大，导致煤层渗透性普遍较低，对煤层气开发、瓦斯治理、煤矿生产和安全管理造成诸多挑战。为提升煤层渗透性，提出了多种煤层增渗改造技术，其中注气驱替煤层CH₄技术在改善渗透性、提高煤层气回收率方面展现出良好的效果。然而，煤储层注气增产机理研究已积累较多成果，但受限于低渗透煤岩孔隙-裂隙双重介质的强非均质性，注气过程中N₂/CO₂与CH₄在多场耦合作用下的竞争吸附-渗流传输机制仍未完全阐明。因此，有必要建立符合实际条件的气体渗流模型，以精准解析气体运移规律，优化钻孔布局，提高瓦斯抽采效率，从而为煤层气高效开发提供可行依据。研究成果如下：

（1）基于粘滞流、Knudsen扩散及表面扩散机理，结合有效孔隙半径、单重分形维数及气体吸附模型，构建适用于实际条件下的煤心纳米孔隙/微裂隙中气体（He/N₂/CH₄ /CO₂）运移的表观渗透率关系式，通过修正Forchheimer方程，推导出纳米孔隙/微裂隙气体渗流数学模型，从而确定单组分气体在煤心内的渗流范围。

（2）对比分析不同温度和压力条件下单组分气体密度、动力粘度、压缩因子、气体分子平均直径及平均自由程，探讨气体分子物理性质随温度和压力的变化规律，明确温度与压力对于单组分气体影响程度；结合低温氮气吸附实验与高压压汞实验，联合表征某矿某煤层煤样孔隙结构特征，基于单重分形维数方法，确定了该煤样吸附孔的分形维数为2.722，渗流孔的分形维数为2.754，表明其中孔和大孔的结构复杂且不规则，为数学模型的提供了基础支持。

（3）开展气体吸附实验，研究粉状煤和煤心对气体的吸附特性，引入过剩吸附量、绝对吸附量及吸附面积等关键参数，对比分析Langmuir方程与BET方程在表征气体吸附行为方面的适用性，进一步探讨吸附模型与实际吸附过程之间的差异，并筛选Langmuir压力和Langmuir吸附量表征煤心中气体吸附浓度的表征指标，为数学模型的建立提供可靠的数据支撑。

（4）基于准静态实验方法体系开展单组分气体渗流实验，通过引入煤心渗透率、气体渗透性系数、Forchheimer方程、启动压力梯度、雷诺数等多维度参数，研究启动压力梯度、粘滞阻力及吸附力对于气体渗流行为的影响，探讨煤心中气体非线性渗流的成因。气体在煤心中的运移过程存在临界压力并确定其具体数值，同时深入分析该临界压力的形成机制。本研究验证了纳米孔隙/微裂隙表观渗透率关系式、纳米孔隙/微裂隙内渗流模型的准确性和可靠性，表明上述模型能够较为准确地描述煤心中的渗流行为，为注气驱替煤层CH₄的现场应用提供了重要的理论依据。

China's coal seam geological structure is complex, with high surrounding rock stress and high-water content, resulting in generally low coal seam permeability, which poses many challenges to coalbed methane development, gas control, coal mine production, and safety management. In order to improve the permeability of coal seams, various coal seam permeability enhancement and transformation technologies have been proposed, among which the gas injection displacement of coal seam CH₄ technology has shown good results in improving permeability and increasing coalbed methane recovery rate. However, there have been many achievements in the study of the mechanism of gas injection for increasing production in coal reservoirs. However, due to the strong heterogeneity of the dual media of low-permeability coal rock pores and fractures, the competitive adsorption permeation transport mechanism of N₂/CO₂ and CH₄ under multi field coupling during gas injection has not been fully elucidated. Therefore, it is necessary to establish a gas permeation model that meets practical conditions to accurately analyze gas migration laws, optimize drilling layout, improve gas extraction efficiency, and provide feasible basis for efficient development of coalbed methane. The research results are as follows:

(1) Based on the mechanisms of viscous flow, Knudsen diffusion, and surface diffusion, combined with effective pore radius, single fractal dimension, and gas adsorption model, an apparent permeability model suitable for gas (He/N₂/CH₄/CO₂) migration in coal core nanopores/microcracks under actual conditions is constructed. By modifying the Forchheimer equation, a mathematical model for gas permeation in nanopores/microcracks is derived to determine the range of single component gas permeation in coal core.

(2) Compare and analyze the density, dynamic viscosity, compression factor, average diameter of gas molecules, and average free path of single component gases under different temperature and pressure conditions, explore the changes in physical properties of gas molecules with temperature and pressure, and clarify the degree of influence of temperature and pressure on single component gases; By combining low-temperature nitrogen adsorption experiments and high-pressure mercury intrusion experiments, the pore structure characteristics of a coal sample from a certain mine and coal seam were characterized. Based on the single fractal dimension method, the fractal dimension of the adsorption pores in the coal sample was determined to be 2.722, and the fractal dimension of the seepage pores was 2.754, indicating that the structure of the pores and macropores is complex and irregular, providing basic support for the mathematical model.

(3) Conduct gas adsorption experiments to study the adsorption characteristics of powdered coal and coal cores for gases, introduce key parameters such as excess adsorption capacity, absolute adsorption capacity, and adsorption area, compare and analyze the applicability of Langmuir equation and BET equation in characterizing gas adsorption behavior, further explore the differences between adsorption models and actual adsorption processes, and screen Langmuir pressure and Langmuir adsorption capacity as characterization indicators for gas adsorption concentration in coal cores, providing reliable data support for the establishment of mathematical models.

(4) Based on the quasi-static experimental method system, single component gas permeation experiments were conducted. By introducing multidimensional parameters such as coal core permeability, gas permeability coefficient, Forchheimer equation, starting pressure gradient, Reynolds number, etc., the effects of starting pressure gradient, viscous resistance, and adsorption force on gas permeation behavior were studied, and the causes of nonlinear gas permeation in coal core were explored. The migration process of gas in coal core has a critical pressure and its specific value is determined. At the same time, the formation mechanism of this critical pressure is analyzed in depth. This study verified the accuracy and reliability of the relationship between apparent permeability of nanopores/microcracks and the flow model within nanopores/microcracks, indicating that the above models can accurately describe the flow behavior in coal cores, providing important theoretical basis for the field application of gas injection to replace CH₄ in coal seams.

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