低渗煤层多尺度煤体全尺度孔裂隙瓦斯运移联动机制与模型

The existing gas mechanism and models of porous media are inadequate to describe the gas migration process in low permeability coal seam. It is not clear about the correlation mechanism of gas migration mechanism in multi-scale coals. The project adopts the method of theoretical analysis, mathematical modeling, laboratory experiment and numerical simulation. The following three aspects of research are going to be investigated: ①Based on Boltzmann molecular motion theory and the micro-motion characteristics of gas molecules in the nanoscale-pores of coal, a new theory and model of multi-scale pores gas migration based on wide area Knudsen number are about to be developed. The model will be verified by experiment of gas flow through Anodic alumina film. ② By data fusion, determination method and tree fractal characterization method of full scale pore and fracture of coal and are established. Find out The fractal characteristics of pore structure in coal with different scales are studied. Digital pore network diagrams of several typical scales coal are constructed. Calculating intrinsic permeability by LBM method. ③ Integrating the fractal dimension and the equivalent flow radius into the new model, the mathematical model of gas migration in multi-scale coal with different-scale pores networks is established. Based on experiment verification and numerical modeling verification and scale effect analysis of coal gas migration, typical coal scale boundary and REV scale are about to be determined. Then gas migration mechanism correlation of different scales coal and enhancing permeability mechanism under the condition of real low permeability coal seam with different gas pressure and ground stress are about to be investigated by numerical simulation.

现有多孔介质气体机制和模型不能准确描述低渗透煤层瓦斯运移过程，多尺度煤体孔裂隙瓦斯运移关联机制还不清楚，缺少广域Knudsen数的瓦斯动力学理论和模型。拟采用理论分析、数学建模、实验室实验和数值模拟相结合的方法，开展以下研究：①基于Boltzmann分子运动理论，分析纳米级煤岩孔隙内过渡流态的气体分子运动微观特征，建立广域Knudsen数的多尺度孔隙瓦斯运移新理论和模型，通过氧化铝薄膜实验验证模型；②通过数据融合，建立全尺度孔裂隙的测定与树型分形表征方法，研究不同尺度煤体的孔隙结构分形差异特征，构建数字化煤芯孔隙网络图，采用LBM法计算固有渗透率；③引入分形维数和等效流动半径，建立多尺度煤体（不同孔裂隙管束）瓦斯运移物理数学模型；实验和数值模拟验证的基础上，分析煤体瓦斯运移规律的尺度效应，确定典型煤体尺度边界和REV尺度，模拟考察真实低渗煤层条件下，多尺度煤体瓦斯运移机制关联性和增透机理。

项目根据《申请书》和《计划任务书》研究目标、内容和方案，首先考虑了微纳米尺度孔隙的微观边界效应，建立了适用于广域努森数多流态的多尺度孔隙气体流动理论与控制模型。选用8种类型氧化铝薄膜，开展了60次等径均匀微纳米孔隙气体流动规律实验研究，验证了新模型，查明了孔径和孔隙压力等对流动状态和渗透率的影响。其次，采用工业CT扫描等煤体全孔径孔裂隙结构差异测定方法和分形理论，开展了8种尺度的煤体孔裂隙特征研究，构建了三维数字煤芯的孔裂隙结构图，查明了煤的孔裂隙结构参数和分形维数随煤体尺度的变化规律，揭示了粒度和煤分子结构对变形煤和未变形煤之间吸附能力影响的差异性特征，建立了煤体微纳米孔隙瓦斯流动MRT-LBM模型，可用于计算煤体固有渗透率，扩展模拟了煤层纳米孔隙气体流动规律。第三，建立了煤粒多尺度孔隙动态扩散新模型、煤体多尺度瓦斯运移视渗透率模型、动态表观渗透率与动态表观扩散系数的转换关系，开展了典型尺度煤体瓦斯运移规律实验研究与模型验证，分别从煤粒、标准试件和煤层尺度研究了低渗煤层瓦斯运移的多尺度联动机制。研究结果表明，新模型实现了跨尺度孔隙气体流动规律描述，视渗透率与固有渗透率比值随孔隙极限尺度、分形维数、迂曲度、气体压力和努森数呈规律性变化，即微观边界效应增强，实际气体流动能力增大；高变质程度分形维数随着煤体尺度的减小而增加，而中变质程度D2值反之，煤体尺度的减小降低了其异质性；吸附层会减小孔隙有效流动半径，减弱孔隙气体流动能力；稳态法、脉冲衰减法（传统方法）仅可以测定煤体大孔裂隙中的渗透率，基于多尺度动态综合表观渗透率模型可实验测定包含微纳米孔隙的煤体固有渗透率；基于渗透率时空变化规律的“一孔多措”动态增透机制可显著提高增透效果和高效抽采时间。发表学术论文16篇，授权发明专利3项，出版专著2部，获河南省科技进步二等奖等省部级奖励3项，5次国际会议特邀报告，培养博士2名，硕士8名，博士后3名。