煤层瓦斯微纳米串联多尺度动态扩散渗透率实验-模型-机理及意义  

Experiment,modelling,mechanism and significance of multiscale and dynamic diffusionpermeability of gas through micro-nano series pores in coal

作　　者：李志强[1,2,3,4] 陈金生 李林[1,2] 彭建松[1,2] LI Zhiqiang;CHEN Jinsheng;LI Lin;PENG Jiansong(MOE Engineering Center of Mine Disaster Prevention and Rescue,Henan Polytechnic University,Jiaozuo 454000,China;Collaborative Innovation Center of Coal Work Safety and Clean High Efficiency Utilization,Henan Polytechnic University,Jiaozuo 454000,China;Collaborative Innovation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region(Henan Province),Henan Polytechnic University,Jiaozuo454000,China;Henan Provincial Key Lab of Gas Geology and Control-Cultivation Base of Provincial and Ministry Joint State Key,Henan Polytechnic University,Jiaozuo 454000,China)

机构地区：[1]河南理工大学煤矿灾害预防与抢险救灾教育部工程研究中心,河南焦作454000 [2]河南理工大学煤矿安全生产与清洁高效利用省部共建协同创新中心,河南焦作454000 [3]河南理工大学中原经济区煤层/页岩气河南省协同创新中心,河南焦作454000 [4]河南理工大学河南省瓦斯地质与瓦斯治理重点实验室−省部共建国家重点实验室培育基地,河南焦作454000

出　　处：《煤炭学报》2023年第4期1551-1566,共16页Journal of China Coal Society

基　　金：国家自然科学基金资助项目(52174173);河南理工大学博士基金资助项目(B2018b258,B2021b27)。

摘　　要：多尺度科学问题作为当前世界科学前沿的热点问题之一,已拓展到自然科学与工程技术的众多领域,作为多尺度科学的一个分支,煤岩渗流力学亦存在自身的多尺度科学问题。煤体中存在从毫米到微纳米的多尺度孔裂隙,孔径量级可达百万倍之巨,这使得煤体渗透率也呈现出百万量级的空间与时间多尺度特征。因而,煤体多尺度渗透率研究既是煤岩渗流力学的学科内涵问题,亦是瓦斯抽采亟需的工程外延问题。采用柱状原煤煤心开展了无应力和三轴应力下CH4/He的非稳态扩散-渗流实验和三轴应力下稳态渗流实验。实验结果表明:柱状煤心的表观扩散系数随时间延长而动态衰减,并呈现出2类时间多尺度特征,一种为连续光滑的动态衰减特征,一种为两阶段阶跃式动态衰减特征。导出了动态表观扩散数学模型,该模型能较准确描述柱状煤心中气体(CH4/He)非稳态流动全过程。提出了多管串联多尺度孔隙结构物理模型和数学模型,采用压汞孔径数据验证了串联多尺度孔径模型,并据此给出了串联多尺度渗透率的数学证明。以努森数(Kn)为标准,划分了连续流-滑移流-过渡流-自由分子流等流域,以串联多尺度孔径为关联纽带,建立了考虑有效应力和流态的多尺度渗透率模型。研究结果揭示了煤层瓦斯串联多尺度渗流机理,即煤体微纳米孔径及其串联级数是影响多尺度渗透率的决定性因素,可测孔径范围内多尺度效应影响程度可达数万量级。流动初期,气体首先从外层大孔裂隙中流出,流动后期,逐渐从微小孔隙中流出,直至深达纳米级孔隙。随着时间延长,串联孔隙级数逐渐增长,等效孔径逐渐减小,其量级接近于最小孔径,进而使得等效渗透率随时间延长而急速衰减,渗透率的时间多尺度动态衰减特征是空间多尺度的外在反映。气体流动后期,努森数增大,滑移-过渡流态效应超�As one of the hot issues at the frontiers of science in the world,the multi-scale scientific question has occurred in the fields of natural science and engineering.The seepage in coal-rock,a branch of the multi-scale science,shows its multi-scale scientific question.Coal is a porous medium that contains multi-scale pores with the aperture from millimeter to nanometer.The pore size differential can reach one million orders of magnitude,which causes the multi-scale characteristics in space and time for coal permeability.Therefore,the research on the multi-scale permeability of coal is a critical scientific issue of the coal gas flow as well as an engineering extension of methane drainage.The unsteady diffusion-seepage experiment is conducted for CH4/He with and without stress using a cylindrical coal sample,accompanied by steady state seepage experiment.The experimental results show that the apparent diffusion coefficient of a cylindrical coal sample attenuates with time.This apparent diffusion coefficient shows two different multi-scale characteristics in time,the smooth and dynamic attenuation and the dynamic attenuation in a two-stage step.A dynamic model for the apparent diffusion coefficient is proposed,and it can accurately describe the complete unsteady flow process of gas in a cylindrical coal sample.The physical and mathematical models of the multi-scale pores in series are put forward.Then,the multi-scale structure of pore in series is validated by the mercury injection experiment.After that,the multi-scale permeability model is mathematically proved.Based on the Knudsen number(Kn),the continuous flow,slip flow,transition flow and free molecular flow are identified and introduced with the multi-scale pore size to build a multi-scale permeability model that reflects the effect of the effective stress and gas flow regime.The mechanism of the multi-scale seepage is revealed in this study.The size and the number of pores in series connection are the critical factors to influence the multi-scale permeability.T

关 键 词：多尺度 动态 渗透率 扩散 微纳米孔 

分 类 号：TD713.2[矿业工程—矿井通风与安全] P618.11[天文地球—矿床学]