1. Henan Provincial Key Lab of Gas Geology and Control-Cultivation Base of Provincial and Ministry Joint State Key,Henan Polytecnnic University,Jiaozuo　454000,China;2. State Key Laboratory of Coal Mine Disaster Dynamics and Control,Chongqing University,Chongqing　 400030,China;3. Collaborative Inno-vation Center of Coalbed Methane and Shale Gas for Central Plains Economic Region,Henan Province,Henan Polytecnnic University,Jiaozuo　 454000,China

为解决经典扩散模型不能准确描述煤粒瓦斯全时扩散的科学问题。采集我国典型矿区的代表性煤样,开展了各种条件下的煤粒瓦斯扩散实验。采用经典扩散模型拟合实验表明,某时刻前,扩散率的实验值大于理论值,此时刻后,实验值小于理论值,此规律惟一。经典扩散模型不能准确描述瓦斯扩散全过程,误差极大,进而发现了煤粒瓦斯扩散系数随时间延长而衰减的特有现象。为此,提出了煤粒多尺度孔隙分布的新物理模型,新模型假设煤粒中孔隙呈非均质多尺度形态分布,并具有自相似分形结构,这种多尺度分形结构孔隙决定了煤粒扩散系数的多级分布,进而决定了瓦斯宏观扩散力学机理,即,煤体由表及里,孔隙由大到小分级分布,其扩散系数亦相应的由大到小逐级递减。扩散初期,瓦斯从扩散系数较大的大孔隙中快速逸出,扩散后期,从扩散系数较小的小孔隙中慢速逸出,直至深达微孔内部。正是这种逐级递减的孔隙形态及相应的多级扩散系数分布,形成了瓦斯扩散系数随时间延长而衰减的扩散机理。根据这一物理假设,引入初始扩散系数D0、扩散系数衰减系数β两个参数反映扩散系数动态衰减特征,提出了动扩散系数数学模型,经200余组数据检验,新模型能较准确描述各条件下的煤粒瓦斯(CH4,CO2,N2)扩散全过程。新模型涵盖了经典单孔隙扩散模型和双孔隙模型,将其推广到了多孔隙维度,并能解释经典单孔隙扩散模型出现的问题,新模型在准确性、简单性、解释性、预测性上优于国外双孔隙模型及其它经验公式。多尺度动扩散系数扩散模型为准确计算瓦斯(煤层气)含气量、储量、突出预测指标,解释各种条件下的瓦斯扩散机理提供了新物理模型和计算新方法。

In order to solve the problem that the classical diffusion model cannot accurately fit a full-time gas diffusion process in coal particle,the experiments of gas diffusion in coal particle were carried out under various conditions using typical coals in China. The results calculated by classical diffusion model show that the experimental values of diffusion ratio are greater than the theoretical value before a certain time,however,the former is less than the latter after that time. The classical diffusion model cannot precisely fit a full-time gas diffusion process and the error is large,and then the special phenomenon for diffusion coefficient decrease with the increase of time was found. The new physical model of multi-scale pore distribution in coal was put forward. Based on new model,the authors assumed that the pore distri- bution within coal is heterogeneous and multi-scale,and has self-similar fractal structure,which causes the multistage distribution of diffusion coefficient within coal and determines the macroscopic diffusion mechanism of gas. From the surface to the center of coal,the pore distributes from big to small and the diffusion coefficient decreases accordingly. Gas diffuses rapidly from the big pore with large diffusion coefficient in the early stage and slowly from the small pore with small diffusion coefficient in the late stage until the micro pore is finally influenced. The multilevel diffusion coef- ficient distribution caused by multi-size pore results in the diffusion mechanism of diffusion coefficient decease with the increase of time. According to the assumption,two parameters,initial diffusion coefficient ( D0 ) and decay coefficient (β),were introduced to reflect the decay characteristic of dynamic diffusion coefficient. The mathematic model of dy- namic diffusion coefficient was put forward. The new model,verified by 200 data,can fit the full-time process of gas diffusion in coal under various conditions. Meanwhile,the new model covers the classical unipore diffusion model and bidisperse one and generalizes the latter ones. The new model can explain the problems caused by classical one,and in terms of accuracy,simplicity,explanatory and predictability,the new model is better than the bi-disperse model and empirical equations. The new model provides a new algorithm to determine coalbed methane content,reserves and out- burst predicting index and to explain the diffusion mechanism under various conditions.

国家自然科学基金资助项目(51004041)；长江学者和创新团队发展计划资助项目(PCSIRT1235)；煤矿灾害动力学与控制国家重点实验室开放课题资助项目(2011DA105287-KF201313)；

Li Zhiqiang,Liu Yong,Xu Yanpeng,et al. Gas diffusion mechanism in multi-scale pores of coal particles and new diffusion model of dy- namic diffusion coefficient[J]. Journal of China Coal Society,2016,41(3):633-643.