煤体结构制约下的煤层气渗流机理研究

There are various types of tectonically deformed coals in China, which are widely distributed and contain a large amount of coalbed methane (CBM) resources. However, there are significant differences in the pore and fracture structure of different tectonically deformed coals. The CBM exploration and development in tectonically deformed coal developed regions in China is still seriously hindered, due to the unclear understanding of CBM percolation mechanism of different tectonically deformed coals. To solve the above problems, this project intends to take the Hancheng block in the eastern margin of the Ordos Basin as the research object, through field test and experimental analysis, clarify the reservoir physical properties of tectonically deformed coals and their controlling factors. Using CT scanning system, combined with stress and pore pressure loading device, the three-dimensional reconstruction of tectonically deformed coals with different geological conditions is carried out. Then the seepage simulation of the reconstructed model is carried out by the lattice Boltzmann method, and the pore and fracture system and seepage characteristics of tectonically deformed coals under in-situ formation conditions are described. Moreover, this research will carry out simulation experiments of CBM production in the tectonically deformed coals, and discuss the dynamic change law of permeability as well as CBM percolation mechanism of different tectonically deformed coals, which will provide the scientific basis for the effective develop of CBM resources in the tectonically deformed coal developed regions.

我国构造煤类型多样，分布广泛，蕴含大量的煤层气资源，但不同煤体结构煤储层孔裂隙结构发育特点存在显著差异，迄今对不同类型构造煤中煤层气的渗流机理认识不清，严重阻碍了我国构造煤发育区的煤层气勘探与开发。针对上述问题，项目拟以鄂尔多斯盆地东缘韩城区块为研究对象，通过现场观测和实验分析，精细描述构造煤储层孔裂隙结构差异特点，厘定构造煤储层物性显现特征及其主控因素。运用CT扫描系统，结合应力和孔隙压力加载装置，对不同地质条件下的构造煤孔裂隙系统进行三维重构，利用格子玻尔兹曼方法对重构的模型开展渗流模拟，阐明原位地层条件下的构造煤孔裂隙微观结构及其渗流特征；同时开展甲烷在构造煤中的渗流产出模拟实验，查明不同类型构造煤储层渗透率动态变化规律，厘定煤体结构制约下的煤层气渗流机理，为构造煤发育区煤层气的开发提供科学依据。

我国构造煤类型多样，分布广泛，蕴含大量的煤层气资源，但不同煤体结构煤储层孔裂隙结构发育特点存在显著差异，迄今对不同类型构造煤中煤层气的渗流机理认识不清，严重阻碍了我国构造煤发育区的煤层气勘探与开发。在此背景下，本项目以鄂尔多斯盆地东缘韩城区块为研究对象，通过现场煤岩观察、室内实验测试、测井数据反演、动态数据分析等方法，精细描述了构造煤储层孔裂隙结构发育特征，揭示其在煤体结构制约下的煤层气渗流机理。结果表明，研究区构造煤储层测井数据表现为低密度、高声波时差、大扩径和低电阻率的特点，以煤体结构指数N和深侧向电阻率与微球聚焦电阻率比值R双参数交汇图的方法将构造煤类型分为三种。研究区三类构造煤及原生结构煤样品的室内实验测试结果表明，随破坏程度增加，微孔孔容贡献度呈先增后减的规律，中孔孔容贡献度呈增大趋势，大孔孔容贡献度先减后增，DFT比表面积在原生结构煤到碎裂煤阶段上升，从碎裂煤到糜棱煤阶段下降。碎裂煤、糜棱煤、碎粒煤和原生结构煤在同一条件下，甲烷渗透率依次降低。在有效应力作用下，煤岩渗透率随有效应力的增加均呈负指函数下降，碎裂煤的表现出最高的应力敏感性，结合X-ray CT扫描结果表明，在构造煤中呈板状、条带状分布的A型裂隙在有效应力作用下被压缩程度最大，而碎裂煤中该型裂隙发育最为平整和广泛，在有效应力条件下渗流通道产生大量闭合，导致渗透率下降，但在不同方向渗透率损失率不同，因此构造煤发育区煤层气开发过程中，碎裂煤发育区储层虽具有较强的渗透性，但其储层物性变化在应力作用下较为敏感，为避免开采过程中渗流通道的闭合，应注意开采时的施加的应力系统与煤层裂隙走向的配置关系。