煤层气地面开采过程中储层的渗透性动态变化规律及其控制机制

Permeability of coal is a key parameter in controlling movement of coalbed methane （CBM） in coal reservoir.It is very important for evaluating the region selection of CBM exploration and development and the productivity of CBM wells to study on the control factor on the permeability and its dynamic change law during CBM production. This project will carry out a series of experimental and numerical simulations by means of mock up tests based on the condition of coal reservoirs in china. The project aims to: 1) studying on the distribution characteristics of the stress and its control law on coal-rock mechanical properties and pore/fracture based on different tectionic and thermal evolutions, further discussing on the major factors that cause the permeability and its diversity of coal reservoirs. 2)Analyzing the influencing rule on the rock mechanical properties of coal body and pore/fracture structures because of the change of the gas-liquid-solid phase medium and the stress condition during CBM ground mining, discussing about the the progressive interaction among the desorption/adsorption-induced shrinkage/swelling characteristics of coal matrix, the pore/fracture structures in coal, and the reservoir permeability. 3)Further, investigating the control mechanism of the dynamics evolution of the reservoir permeability due to the dynamic characteristics of the various factors, Constructing a mechanical-mathematical model of the reservoir permeability. The project will further enrich and improve the geologic theory and method to evaluate the coal reservoir permeability, and provide added theoretical and practical values for CBM exploration and development in China.

煤的渗透性是控制煤层气在煤储层中流动的关键参数，研究煤层气排采过程中，渗透性的动态演化规律及其控制因素，对煤层气勘探开发、选区评价和煤层气井产能具有重要的理论意义和实践价值。 本项目基于我国煤层气储层实际，拟通过一系列煤岩学、岩石力学等实验测试和储层数值模拟分析，研究在不同构造、热演化背景下，煤层所处的构造应力环境对煤岩力学性质以及孔裂隙性的控制规律，探明储层原始渗透性及其差异性的主控因素；耦合分析煤层气排采过程中，排水降压造成的固、气、液三相介质与所处的应力环境的变化对煤岩力学性质、储层孔裂隙系统的影响规律，探讨煤基质胀缩性-孔裂隙性-渗透性的递进控制关系；揭示各因素改变对储层渗透性动态演化的控制机制，构建煤层气排采过程中的储层渗透性动态变化数学-力学模型。项目研究将进一步丰富和完善煤储层渗透性研究的地质理论和方法体系，对我国煤层气勘探开发具有重要的理论和实践价值。

项目基于我国煤储层地质构造特征以及煤层气产出的地质背景，以及煤储层渗透性的特殊性和复杂性，开展了一系列常规煤岩煤质测试分析、煤的吸附/解吸性、扩散性、渗透性以及吸附膨胀实验，探讨了气体介质吸附过程中煤体的应变与煤级、围压、有效应力以及气体介质的关系，模拟分析了煤层气开采过程中，因排水降压造成的气体解吸引起基质收缩对煤的渗透性的影响规律，并揭示其原因；根据不同溶剂对煤样的萃取/溶出改造实验结果及相关参数测试结果，分析了改造后前后煤样的化学组成和结构、物性特征等差异性及变化规律，揭示了不同类型的溶剂作用下，煤的物性和组成变化特征及其实质，提出了不同类型溶剂做为压裂液的可行性；基于高阶煤的孔裂隙性、吸附解吸性、扩散性以及煤层气井现场自然解吸数据, 系统探讨了构造破坏作用下高阶煤的孔隙性、吸附性、扩散性、渗透性等物性的响应规律, 揭示了不同煤体结构的高阶煤的解吸、扩散特征及其影响因素，构建了相应的孔裂隙几何模型、解吸－扩散－渗流过程的地质模型以气体运移模式图。研究成果进一步丰富和完善了煤储层物性特征及储层改造理论，也对煤储层压裂及排采管控，及煤矿井下瓦斯防治具有指导价值。