内在水-瓦斯-煤耦合作用下低阶煤双重渗透率演化机制研究

Low-rank coal is mainly distributed in the coal-bearing basins of western China and has the characteristics of high inherent moisture content. Inherent moisture exists in coal matrix pores by physical adsorption. It will causes the change in pore structure of coal, affects the characteristics of coal matrix skeleton, and further significantly controls the evolution law of coal permeability, which is an important restraining factor for gas flow and extraction effect. Based on the theoretical analysis, laboratory experiments, numerical simulation and field tests, the distribution of inherent moisture in low-rank coal and the response characteristics of pore structure to inherent moisture will be studied, then obtain the quantitative equation of inherent moisture and the quantitative description method of pore adsorption water film; the mechanism of adsorption induced coal deformation considering the inherent moisture-gas-coal coupling effects will be analyzed and its theoretical model will be built; and reveal the control effects of adsorption induced coal deformation on permeability under the coupling effects by combining the seepage test results; further deduce the dual permeability model for coal matrix pores and fractures considering the combined effects of the adsorption water film, adsorption induced coal deformation and effective stress, then the change law of permeability with inherent moisture will be analyzed; finally, the multi-filed coupling model of inherent moisture-gas-solid for gas migration in low-rank coal seam will be constructed, which will provide a numerical approach to analysis the impact of inherent moisture on gas migration field and extraction effect. This research can be used to guide the designs of technical scheme and optimizations of parameters in the gas extraction project of low-rank coal mines.

低阶煤主要分布于我国西部地区含煤盆地，具有高内在水含量的特点。内在水分布于煤基质孔隙，以物理吸附形式赋存，会造成煤孔隙结构改变，并显著影响煤基质骨架特征，进而控制煤渗透率演化，是制约瓦斯流动和抽采效果的重要因素。项目采用理论分析、实验室试验、数值模拟与工程验证相结合的方法，研究低阶煤内在水分布及内在水作用下煤孔隙结构响应特征，获得内在水量化方程与孔隙吸附水膜定量描述方法；分析内在水-瓦斯-煤耦合作用下的煤吸附变形机制并建立数学模型，结合渗流测试结果揭示内在水-瓦斯-煤耦合作用下煤吸附变形对渗透率的控制作用；进一步构建综合考虑孔隙吸附水膜、煤吸附变形及有效应力作用的基质-裂隙双重渗透率模型，分析其随内在水含量的演化规律；在此基础上，建立低煤阶煤层瓦斯运移湿-气-固多场耦合模型，用于解算分析内在水对瓦斯流场与抽采效果的影响规律。研究成果可为低阶煤矿井瓦斯抽采工程的设计与抽采参数优化提供指导。

我国低煤阶煤炭储量丰富，主要分布于我国西部地区的含煤盆地。低阶煤赋存较高含量的内在水，内在水会影响煤-瓦斯相互作用，并与瓦斯气体共同改变煤基质骨架变形特征，进而控制煤体渗透率演化，成为制约低煤阶煤层瓦斯流动和瓦斯抽采效果的重要因素。项目综合采用理论分析、实验室试验、数值模拟与现场工程相结合的方法开展了相关研究，主要获得如下结论：1）预吸附水分对大于10nm孔隙的影响并不明显，而对于微孔（<10nm）的比表面积和孔容具有显著的弱化作用，并且在高含水率条件下内在水分布会对气体分子侵入煤微孔产生显著的阻塞作用；2）构建了考虑内在水-瓦斯共同影响的煤岩吸附变形模型，揭示了水与瓦斯气体共同吸附导致的煤体变形机制，并通过静水压条件下不同含水率煤样的渗透率演化试验，获得了内在水对煤岩瓦斯渗流特性的影响，揭示了内在水与瓦斯共同影响下煤岩吸附变形对渗透率的控制作用；3）建立了考虑孔隙水膜、煤吸附变形及有效应力作用的基质-裂隙双重渗透率演化模型；进而基于构建的低煤阶煤层瓦斯运移湿-气-固多场耦合模型，数值模拟获得了内在水引发煤岩物性参量变化条件下抽采工程中渗透率、瓦斯压力的时空演化规律，掌握了内在水对低煤阶煤层瓦斯运移的影响特征。依托项目发表标注国家自然科学基金项目资助（51804201）的学术期刊论文6篇，其中SCI/EI检索论文5篇，获得授权国家发明专利1件、授权实用新型专利1件、处于实审阶段的国家发明专利2件，指导在读硕士研究生4名，参加国内外学术会议7次，其中作分论坛小组报告1次。研究成果能够为低煤阶煤层瓦斯抽采工程设计及瓦斯灾害防治提供理论指导。