煤裂-孔性双重介质中煤层气吸附/解吸运移机理的分形研究

To better understand the migration mechanism of coalbed methane(CBM) and accurately assess its productivity, we focus our attention on three basic problems existing in the seepage of CBM: the effect of dual-porosity pore structure with fractal behaviors on the permeability of coal reservoir, the inducing mechanism of the adsorption/desorption process for methane, and the characteristics of the transient flow resulting from multi-field coupling effect and its influence on the transport property of coal. In this project, the kinetic theory is adopted as the primary mining tool to explore the basic physics of porous media flow. As a critical step in the current project, we will first investigate the fractal pore-permeability relationship as well as the fracture-permeability relationship in the fracture composite topography with mismatched rough surfaces，and then analytically derive the fractal pore-permeability relationship of coal media with dual-porosity based on the spatial distribution of the cleat/fracture system and the fractal matrix pore structure. Sequentially, with the results of the adsorption/desorption experiments, we will analogically explore the inducing mechanism of such a process by borrowing the photoelectric effect theory, and analytically derive the rock mechanics characteristics of expansion and contraction in pore space. By the lattice springs model (LSM), we will also characterize the dynamic micro deformation in pore space, and develop a lattice Boltzmann model to govern the flow of CBM, which couples the adsorption/desorption processes. Furthermore, we will carry out the interaction between the LSM and LBM systems by the collision operation among fluid particles,and simulate the organic coupling of multiple fields and the process of transient flow. Based on the transient flow of CBM, we will analyze the effect of multi-fields and ultimately establish the seepage law. The solutions to these key issues in this study may bring about some breakthroughs in the seepage theories of coalbed methane, thus laying the theoretical foundation and providing technical support for the exploitation potentiality evaluation of CBM as well as for its highly efficient exploitation and utilization.

探明双重孔隙结构对煤层气运移的控制作用，发掘其吸附/解吸诱发机制,再现多场耦合的瞬变流过程及其对储层输运属性的影响，是理解煤层气运移机理并实现其产能准确评估的基础。本课题拟以分子动理论为多孔介质流基础物理的发掘工具，于孔隙尺度分析煤岩基质分形孔-渗关系及端面粗糙复合形貌空间下裂-渗方程，并依据割理/裂隙的空间分布解析建立裂-孔性双重介质的孔-渗分形关系；在此基础上，结合煤层气吸附/解吸实验结果，借鉴"光电效应"来分析甲烷的吸附/解吸诱发机制，并推演煤介质孔隙空间膨胀/收缩的岩石力学特征；进而采用格子弹力模型来表征孔隙空间的动态形变，并发展一种耦合吸附/解吸过程的格子波尔兹曼渗流控制体系，利用流体粒子间的碰撞来实现多场的有机耦合及瞬变运移过程的模拟，最终建立煤层气的渗流模型。课题关键问题的解决，有望在煤层气渗流理论方面有所突破，为煤层气开采潜力评估及高效开发利用提供理论依据和技术支持。

探明双重孔隙结构对煤层气运移的控制作用，发掘其吸附/解吸诱发机制，再现多场耦合的瞬变流过程及其对储层输运属性的影响，是理解煤层气运移机理并实现其产能准确评估的基础。为此本课题着重开展了基础理论及应用基础理论两个方面的研究，具体如下：.1、基础理论方面：（1）发展的分形拓扑理论，厘清了分形对象中复杂类型以及它们对缩放类型及分形行为的控制作用，实现了自相同、自相似、自仿射以及多重分形属性的统一定义，阐明了尺度不变属性的本质内涵，构建了包含任意缩放对象及分性行为的开放数学框架；（2）基于分形拓扑理论，实现了储层物性的精细描述与定量表征，源头统一了单尺度与多尺度，随机与确定，各向异性与非均质性的数学定义。.2、应用基础理论研究方面：.（1）裂隙流方面：提出了裂隙流三重效应模型，并发展了分形裂渗方程；发展了一种非匹配自仿射裂隙复合形貌表征方法，并验证了三重效应的有效性；等效构建了割理网络模型，系统分析了端、面割理对其渗透率的差异性贡献；（2）多孔介质流方面：发展了一种分形致密储层表征方法，给出了广义孔-渗关系方程；阐明了KC常量的物理意义，建立了其参数化预测模型；实现了一种任意复杂多孔介质水文弯曲度定量计算方法，并给出了颗粒填充型分形多孔介质弯曲度—孔隙度分形预测模型；（3）吸附解吸方面：厘清了储层分形拓扑体系，建立了多孔介质孔-吸关系模型(单层)；提出了分形覆盖率概念，推演了粗糙表面等温吸附模型（5）参数化了地学领域中非线性现象与过程，阐明了行为、原始复杂性的本质差别，在应用方面具体包括分形QSGS方法的发展，双孔隙度模型的构建，压裂过程各向异性属性响应等。.以上研究为定量储层地质学的发展提供了基础理论支撑，为分线性动力学机理的发掘提供了技术支持。