考虑吸附解吸与有效应力耦合作用的煤岩渗透性演化机理研究

Coalbed methane (CBM) resources in China are abundant but the recovery factor is extremely low. One of the main reasons is the lack of research and understanding in coal permeability evolution during CBM extraction process. To address this issue, this project aims to conduct laboratory experimentation, theoretical analysis, and numerical simulation to explore the evolution mechanisms of coal permeability considering the effects of adsorption/desorption and stress dependency, and their interactions. Sorbing gas permeability tests will be performed under different stress paths, while coal swelling strain induced by adsorption and shrinkage induced by desorption will be measured. The competing processes of permeability increment due to desorption and permeability decline due to increase in effective stress during CBM extraction will be carefully and systematically monitored and analyzed. The net permeability evolution under all impacting aspects will be investigated. Furthermore, utilizing dual porosity and dual permeability poromechanics, fluid mechanics, and damage mechanics, a mechanistic permeability evolution model will be developed taking account of the coupling effects of adsorption/desorption-flow-stress. Finite element method will be applied to develop a program to simulate coal permeability evolution for CBM recovery. The program will be validated against both laboratory and field data and improved based on that. The findings of this project will provide theoretical foundations and analytic techniques for improving CBM recovery factor, with broad and promising application in the energy industry.

目前我国煤层气资源丰富但采收率极低，对煤层气开采过程中煤岩体渗透性演化规律的研究不足，认识不充分是重要原因之一。本课题拟采用试验研究、理论分析与数值模拟相结合的方法，研究吸附/解吸-应力耦合作用下的煤岩渗透性的演化机理。开展不同加卸载应力路径下吸附性气体在煤岩中的渗透性试验，分析吸附/解吸过程对煤岩产生的膨胀/收缩变形的影响规律，研究吸附/解吸与有效应力对渗透性变化的互逆过程，揭示多因素耦合作用下煤岩渗透性的演化机理。利用双重介质力学、渗流力学及损伤力学理论，建立吸附/解吸-渗流-应力耦合模型，分析煤层气运移过程中煤岩渗透性随不同气体减压阶段的变化规律。采用有限元法研发煤层气开采过程中煤岩渗透性演化过程的计算程序，开展数值仿真模拟试验；结合具体工程实践，验证理论模型的可靠性并进行修正。研究成果可为提高煤层气采收率提供理论基础和分析手段，具有广阔的工程应用前景。

我国是世界上煤与瓦斯突出最严重的国家之一。随着开采深度的增加、瓦斯压力的增大和 开采条件的日趋复杂，预测和防治工作仍然充满挑战。本课题拟采用试验、理论分析与数值模 拟相结合的方法，研究解吸-渗流-应力耦合作用下的煤岩渗透性和变形破坏的演化机理。开展 不同应力路径下（恒围压，加轴压；恒轴压，卸围压）的解吸-渗流-变形-破坏试验，分析解 吸过程对煤岩变形及强度的影响规律，研究解吸与有效应力对渗透性变化的互逆过程，揭示多 因素耦合作用下煤岩渗透性和变形的演化机理。利用双重介质力学、渗流力学及损伤力学，建 立解吸-渗流-应力耦合模型，分析煤层开挖过程中煤岩渗透性和变形在不同加卸载阶段的变化 规律。采用有限元法研发煤层开挖过程中煤岩渗透性和变形演化过程的计算程序，开展数值仿 真模拟试验；结合具体工程实践，验证理论模型的可靠性并进行修正。研究成果可为预测煤与 瓦斯突出提供理论基础和分析手段，具有广阔的工程应用前景。