Abstract Understanding the complex transport behavior of methane in coal matrix pores is very important for coalbed methane exploitation. One important approach is to model the transport process of methane in coal matrix nanopores. In this work, we modelled the coalbed methane transport process in coal matrix nanopores, coupling gas adsorption, real (i.e. non-ideal) gas and gas slippage effects, and a new method is proposed to characterize the governing equation of transport flow regime. It was found that the proposed model agreed well with the published data on methane physical properties (viscosity and density) and coal permeability. We also focused on the influence of temperature and pore pressure on the flow regime, Knudsen number, surface diffusion and bulk gas flow in the model. The results indicate that under typical reservoir conditions, the real gas and gas adsorption effects have a significant impact on methane viscosity, density and apparent permeability. It was also found that the mass flow rate of methane by surface diffusion increases when pore pressure increases up to about 5 MPa, but tends to decrease when pore pressure increases above about 5 MPa. For any given pore, the flow mechanism of the bulk gas can change from one mechanism to another as the temperature and pore pressure conditions change. The governing equation of the transition flow regime can be regarded as a weighted superimposition of the slip flow equation and Knudsen diffusion equation. However, under reservoir conditions, the Knudsen diffusion regime and the transition flow regime are negligible. This work will provide a theoretical basis to assist with the effective development of coalbed methane.

中文翻译：

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通过纳米孔耦合多流态的煤层气传输分析模型

摘要 了解煤基质孔隙中甲烷的复杂运移行为对于煤层气开发具有重要意义。一种重要的方法是模拟煤基质纳米孔中甲烷的传输过程。在这项工作中，我们模拟了煤基质纳米孔中的煤层气输运过程、耦合气体吸附、真实（即非理想）气体和气体滑移效应，并提出了一种表征输运流态控制方程的新方法。结果表明，所提出的模型与公布的关于甲烷物理特性（粘度和密度）和煤渗透率的数据非常吻合。我们还关注温度和孔隙压力对模型中流态、克努森数、表面扩散和整体气流的影响。结果表明，在典型的油藏条件下，真实气体和气体吸附效应对甲烷黏度、密度和表观渗透率有显着影响。还发现，当孔隙压力增加到约 5 MPa 时，表面扩散甲烷的质量流量增加，但当孔隙压力增加到约 5 MPa 以上时，甲烷的质量流量趋于降低。对于任何给定的孔隙，随着温度和孔隙压力条件的变化，大量气体的流动机制可以从一种机制转变为另一种机制。过渡流态的控制方程可以看作是滑流方程和Knudsen扩散方程的加权叠加。然而，在储层条件下，克努森扩散状态和过渡流状态可以忽略不计。该工作将为有效开发煤层气提供理论依据。