页岩多矿物相孔隙结构特征及考虑润湿特性的CH4耦合传输机制研究

The study of intrinsic relationship of shale mineral facies, pore structure and gas-water two-phase flow mechanism and the revelation of internal constraint factors of shale gas producing rate and recovery are the problems that need solving urgently for the efficient development of shale gas reservoir. The following studies are conducted on shale samples: First，Focused ion beam- scanning electron microscope system (FIB-SEM) and NDS technology are applied to analyze the shale skeleton mineralogical composition and pore structure to get information about diameter, geometrical morphology and authigenic mineral distribution characteristics which has crucial influence on matrix porosity. When combined with energy spectrum analysis, mineral facies and pore structure image of micro/nano scale shale skeleton particle are obtained; Second,Three-dimensional shale digital core of multiple mineral facies is established by multiple-point geostatistics method. Through modifying the interaction strength parameters between fluid and the solid walls in pseudo-potential Lattice Boltzmann method to simulate the effects of wettability. Through introducing the source/sink term into the evoluation equation in the organic pores near the walls to simulate the adsorption and desorption phenomena. And the mathematical model of gas-water two-phase flow including the mineral facies characteristic is built for calculating shale physical property and gas-water permeability parameters. Third, after the study of mass diffusion mechanism of shale diffident mineral particles in micro/ nano pores, the quantitative relationship between shale physical parameters and flow parameters is established, revealing the influencing mechanism of shale mineral facies characteristics and petrophysics parameters on gas-water two-phase micro-flow characteristics, and thus providing foundation for the exploration of the intrinsic mechanism of shale gas enhanced recovery and high production and development.

阐究页岩矿物成份、孔隙结构及润湿特性对微纳尺度下CH4传质扩散影响机制，揭示影响页岩气采收率的主控因素是实现页岩气藏高效开发亟需解决的基础科学问题。针对涪陵页岩气产区天然样品，拟首先开展聚焦离子/电子双束显微电镜扫描及能谱分析等测试，获取孔隙结构以及对其有关键影响的自生矿物分布特征，应用图像处理技术构建页岩的矿物相及孔隙结构图像；然后，采用多点地质统计学原理构建页岩多种矿物相的数字岩心，实现页岩储集空间类型和矿物微区分布的定量表征；最后，基于多矿物相数字岩心平台，通过修改格子波尔兹曼伪势模型中流体与壁面的相互作用强度参数模拟润湿性的影响，通过在有机孔隙壁面附近演化方程中引入源汇项模拟吸附解吸现象，构建考虑矿物成份和润湿性影响的CH4—水两相耦合传质扩散数学模型并求解，分析矿物成份、润湿特性及孔隙结构参数对CH4传质扩散影响规律和相关关系，为宏观尺度页岩气开采数值模拟方法的研究提供理论基础。

以四川盆地长宁区块龙马溪组页岩样品为分析对象，完成了天然页岩微观孔隙结构特征及多种矿物成分室内测试实验，形成了页岩多矿物成份、复杂孔隙结构的三维数字岩心构建技术及程序实现，除可定量计算页岩物性参数之外，在地球物理测井、页岩气储量核算等相关领域具有广泛应用前景。基于室内实验分析结果，深入分析了页岩介质内CH4传质扩散机理，构建了考虑页岩多种矿物成份以及吸附特性的传质扩散模型，相对于传统模型，能更准确、全面的表征页岩介质中微纳米尺度上的传输机制，明确了了页岩矿物相特征、岩石物理学参数和气—水两相微观运移特征的内在联系。构建了页岩气在有机基岩中解吸、扩散、粘性流渗流模型/建立考虑有机质分布影响的有机基岩、非有机基岩及裂缝耦合的页岩气渗流模型/页岩气耦合渗流模型的数值求解算法，并编制相应程序进行数值模拟实现。通过与矿场专家交流，针对页岩气藏普遍压裂投产的开发方式，进一步研究了长水平段多裂缝同步扩展数学模型，利用裂缝尖端渐近解隐式求解裂缝扩展步长，并采用扩展有限元方法对模型进行了求解。在此基础上，研制了页岩气长水平段多级压裂缝网扩展模拟软件，并成功应用于我国长宁-威远国家级页岩气示范区的威202H1-1压裂改造参数优化中，取得了良好的矿场应用效果。.在项目支持下，项目组在Angew. Chem. Int. Ed., Energy等国内外著名期刊共发表包括学术论文15篇，其中，SCI检索11篇，EI检索3篇，申请获授权相关发明专利4项。