Coalbed methane (CBM) mining has always been plagued by low mining efficiency. CBM-rich areas have high mining efficiency, but their formation is affected by CBM seepage. Through on-site mining, it is found that gas seepage in low-permeability areas presents nonlinear characteristics. In this paper, the causes and rules of nonlinear seepage are analyzed. The pore structure characteristic parameters such as pore size distribution, pore proportion and fractal dimension were obtained by nuclear magnetic resonance technology, and the pore structure characteristics of low permeability coal are analyzed. The results showed that the proportion of porosity was 6.30–11.02% and the proportion of percolation pores was 7.52–19.59%. Both total porosity and percolation pores had fractal characteristics. Aiming at the nonlinear problem of gas seepage law in low permeability coal, the permeability and gas flow data of coal samples under different gas pressures were measured by the self-designed coal core permeability automatic tester, and the gas seepage characteristics of low permeability coal samples are studied. The experiment showed that there was a starting pressure gradient in gas seepage in coal samples, and the relationship between gas permeability and gas pressure turned over at 1.25 MPa, indicating that there is a slip effect in coal pores. Considering the influence of pore structure parameters on the nonlinear seepage characteristics of CBM, the relationships between porosity, tortuosity, pore proportion, and fractal dimension and Kirschner permeability, slippage factor, and starting pressure gradient were fitted. The analysis showed that the pore size distribution characteristics with large proportion of micro-pores in low permeability coal made the pressure gradient required for the internal gas seepage larger, the influence of the slippage effect was enhanced, and the seepage of gas was nonlinear. To conclude, the influence of micro-pores developed in low permeability coal on nonlinear gas seepage was significant.

煤层气（CBM）开采一直受到开采效率低下的困扰。煤层气富集区开采效率高，但其形成受煤层气渗流影响。通过现场开采发现低渗透区瓦斯渗流呈现非线性特征。本文分析了非线性渗流的原因及规律。利用核磁共振技术获得孔径分布、孔隙比例、分形维数等孔隙结构特征参数，分析低渗透煤的孔隙结构特征。结果表明，孔隙度比例为6.30%~11.02%，渗流孔隙度比例为7.52%~19.59%。总孔隙度和渗流孔隙均具有分形特征。针对低渗透煤中瓦斯渗流规律的非线性问题，利用自行设计的煤芯渗透率自动测试仪测量不同瓦斯压力下煤样的渗透率和瓦斯流量数据，得出低渗透煤样瓦斯渗流特性被研究。实验表明，煤样瓦斯渗流存在起始压力梯度，瓦斯渗透率与瓦斯压力关系在1.25 MPa时发生翻转，表明煤孔隙存在滑移效应。考虑孔隙结构参数对煤层气非线性渗流特性的影响，拟合了孔隙度、迂曲度、孔隙比例、分形维数与克氏渗透率、滑移因子、启动压力梯度之间的关系。分析表明，低渗透煤微孔比例较大的孔径分布特征，使得内部瓦斯渗流所需的压力梯度较大，滑移效应的影响增强，瓦斯渗流呈非线性。综上所述，低渗透煤中发育的微孔隙对瓦斯非线性渗流影响显着。