基于PFM-CFD方法的深部煤层流固互馈作用机理研究

The reserves of deep coalbed methane (CBM) resources are abundant in China. Accelerating the efficient development of deep CBM is of great significance to ensure the safety of underground coal mining activities and to build up strategic energy reserves. Deep coal seams are generally located in the geological environment of high in-situ stress, high temperature and high fluid pressure. Besides, micro- to nano-scale pores and fractures are highly developed within deep coal seams. Such features will inevitably result in non-linear elastic-plastic deformation behaviors of coal and non-Darcy characteristics of two-phase gas/water flows, which are difficult to be accurately described with conventional deformation and flow theories at macro-scale. This project attempts to incorporate the characteristics of pore-cleat structure and fluid storage and transport behaviors to i) develop an approach namely phase field modeling (PFM) to describe the non-linear elastic-plastic behaviors of deep coal seams, and ii) establish a coupled simulation approach integrating PFM with computational fluid dynamics (CFD) at micro-scale that considers multiple unique mechanisms of deep CBM reservoirs. On such basis, efforts will be taken to reveal the interaction mechanisms between non-linear elastic-plastic deformation and fluid flow with the aim to realize accurate prediction of CBM production. With all these research targets realized, this project is anticipated to provide a concrete support for the efficient development of deep CBM resources and advance of CBM industry.

我国深部煤层气资源储量巨大，其高效规模化开发对于保障煤矿生产及国家能源战略储备安全具有重要的现实意义。深部煤层一般处于高地应力、高地层温度和高流体压力的“三高”地质环境下，加之煤层中微纳米级孔隙-裂隙系统高度发育，使得深部煤层气开发过程中煤岩弹塑性变形与流体微尺度流动均呈现出复杂的非线性力学特征，传统宏观尺度的理论方法很难有效揭示流固互馈作用的内在力学机制。本课题将综合考虑深部煤层地质环境、孔裂隙结构及流体赋存运移特征，创新发展深部煤岩非线性弹塑性变形相场模拟（PFM）方法，建立一套微观尺度煤层气藏多机理PFM-CFD流固耦合模拟方法，从而更有效地从本质上揭示深部煤层气开发过程中煤岩非线性弹塑性变形与流体流动间互馈作用机理，为实现深部煤层气耦合流动模拟理论方法突破、推动我国深部煤层气高效开发技术发展提供有力支撑。

综合开展低温氮吸附/CO2吸附、扫描电镜、悬滴法润湿性测试等实验，结合微观尺度分子模拟等手段，阐明了煤岩多尺度孔裂隙结构和壁面润湿性特征。考虑裂隙变形和流体流动过程，建立了PFM-CFD耦合模拟方法，基于微流控实验验证了模拟方法的可靠性。在此基础上，考虑原生、破碎、糜棱等不同煤体结构特征，开展了裂隙网络中气水流动的数值模拟研究，明确了不同煤体结构条件下流速对气锁和水锁演化规律及气水两相流动能力的影响规律。