煤岩纳微米孔隙中煤层气运移特性及气-液两相流动机理研究

Based on the adsorption theory, seepage theory and multiphase fluid dynamics theory, as well as the reconstruction of the nano-micro multi-scale three-dimensional structure, this project will systematically investigate the coal bed methane adsorption/desorption, diffusion, seepage and coal bed methane-liquid (containing soluble surfactants) two-phase flow mechanism by developing micro-mesoscopic numerical simulation methods and relevant experiments. It includes establishment of a reservoir model considering heterogeneity of coal surface and developing the molecular dynamics method to simulate the interaction between methane molecules and coal surface so as to reveal the adsorption/desorption micro-mechanism of coal bed methane. According to the micro-scale flow characteristics of gas in nano-micro pores, a three-dimensional lattice Boltzmann model of coal bed methane seepage with the consideration of adsorption/desorption and diffusion effects will be established to revel the coupling mechanism of adsorption/desorption, diffusion and seepage multiphysics processes of coal bed methane. A three-dimensional lattice Boltzmann-finite difference hybrid model of coal bed methane-liquid two-phase seepage considering the effect of soluble surfactants will be established to clarify the coal bed methane-liquid two-phase flow mechanism affected by soluble surfactants. The research of this project not only has important academic significance for deeply understanding the complex transport mechanism of coal bed methane in nano-micro pores of coal rocks, but also has important engineering guidance for accurately predicting coal bed methane, improving coal bed methane recovery rate and optimizing the hydraulic fracturing technology.

本项目重构煤岩纳微米多尺度三维结构，基于吸附理论、渗流理论和多相流体力学等基础理论，发展微介观数值模拟方法并结合实验，系统研究煤岩纳微米孔隙中煤层气吸附/解吸、扩散、渗流及煤层气-液（含表面活性剂）两相流动机理。具体包括：构建考虑煤表面非均质性的储层介质模型，发展分子动力学方法模拟甲烷与煤表面的相互作用，揭示煤层气吸附/解吸微观机理；根据纳微米孔隙中气体微尺度流动特性，建立考虑吸附/解吸和扩散效应的煤层气渗流三维格子Boltzmann模型，探究煤层气吸附/解吸、扩散和渗流多物理过程耦合作用机理；构建考虑表面活性剂效应的煤层气-液两相渗流三维格子Boltzmann-有限差分混合模型，明晰压裂液中添加表面活性剂对气-液两相渗流的影响机制。本项目的开展不仅对深刻认识煤岩纳微米孔隙中煤层气复杂运移机理具有重要学术意义，同时对准确预测煤层气产量、提高煤层气采收率及优化水力压裂技术具有重要工程价值。

项目针对煤岩纳微米孔隙中煤层气运移特性及气-液两相运移机理展开研究。构建了不同孔径尺寸的狭缝孔模型、不同表面缺陷的煤分子模型以及表面活性剂改性的水-煤模型，发展分子动力学方法探讨了温度、压力、湿度、芳香单元堆砌层数等对甲烷最佳吸附位、吸附等温线以及甲烷与煤表面含氧官能团之间相互作用的影响机制，结合煤吸附甲烷实验，揭示了甲烷在不同变质程度煤内的吸附/解吸和扩散机理，为通过调控煤体润湿性促进煤层气解吸扩散提供了理论依据。基于气体动理学理论，发展了直接求解Boltzmann方程的离散速度法，该方法适合求解连续流区、过渡流区、滑移流区和自由分子流区的煤层气运移全尺度模拟，提出了基于Voronoi多面体抛分的多孔介质生成新方法，通过调节方法中的控制参数获得了具有特定要求（如孔喉比、比表面积、分形维数、迂曲度等）的煤岩纳微米孔隙网络模型，编写MPI并行计算程序，研究了纳微米孔隙介质中甲烷、二氧化碳、氮气、氢气等的非线性渗流规律，捕捉到气体渗流过程中的滑脱效应，获得了气体表观渗透率与理论解和实验结果吻合较好，阐明了注入二氧化碳驱替甲烷提高煤层气采收率的可行性，提出了高阶气体表观渗透率预测模型。发展了大密度比气-液两相流动三维等温格子Boltzmann伪势模型，编制OpenMP高性能计算程序，研究了复杂多孔介质中气-液界面张力、壁面润湿性、孔隙率、多孔介质非均质性等对气-液两相流动的影响机制，发现液体在超亲水壁面上迅速铺展，导致气-液两相流动速度加快，超疏水壁面可增大固-液之间的接触角，减小液体与固体壁面之间的摩擦阻力，促进气-液两相流动。发展了基于相场理论的含表面活性剂两相流格子Boltzmann模型，发现表面活性剂会朝向界面形变程度较大的区域迁移，与干净界面相比，含表面活性剂两相流界面在剪切力作用下更容易破裂，揭示了表面活性剂降低界面张力，促进两相流动的机理。本项目为后续开展多物理场的煤层气运移尺度升级研究提供了理论依据、模型基础和算法支持。

内容获取失败，请点击重试