Intrinsic and apparent gas permeability of heterogeneous and anisotropic ultra-tight porous media
Intrinsic and apparent gas permeability of heterogeneous and anisotropic ultra-tight porous media
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DOI：
10.1016/j.jngse.2018.10.003
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发表时间：
2018-12-01
影响因子：
--
通讯作者：
Wu, Lei
中科院分区：
文献类型：
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作者：
Germanou, Lefki;Ho, Minh Tuan;Wu, Lei
非常规天然气产量的准确预测需要对复杂岩石样品的渗透率有深入的了解。近年来，人们提出了几种渗透率的预测表达式，其中包括对多孔介质结构或流动机制的简化。本研究的主要目的是量化固体基质复杂性对固有渗透率和表观渗透率的影响。为此，利用四重奏结构生成集算法构建了大量二维随机多孔介质结构。参数分析和统计分析揭示了孔隙比表面积、弯曲度、非均质性和各向异性程度的重要性。考虑到各向异性对渗透率数据的实验室评价和页岩的各向异性性质的巨大影响，特别关注渗透率对各向异性和各向异性几何形状的方向依赖性。在相同孔隙度值下，模拟结果清楚地表明，由于孔隙比表面积和高宽比的减小，渗透率显著提高。这表明岩石基质复杂性对渗透率有显著影响，在形成多孔介质渗透率公式时不应忽视这一点。最后，结合求解气体动力学方程得到的视渗透率结果，论证了增强比、滑移系数及其与上述参数的相关性。分别考虑连续渗流和滑动渗流，导出了本征渗透率和视渗率的半解析表达式。所提出的公式适用于各向同性和各向异性结构，其优点是不需要任何数值或实验数据作为输入。
Accurate prediction of unconventional gas production requires deep understanding of the permeability of complex rock samples. Several predictive expressions of permeability, which include either simplifications of the porous media structure or the flow mechanisms, have been proposed recently. The main objective of this research is to quantify the impact of solid matrix complexity on both intrinsic and apparent permeability. To this end, numerous two-dimensional random porous media structures are constructed using the quartet structure generation set algorithm. Parametric and statistical analysis reveals the importance of the specific surface area of pores, tortuosity, heterogeneity and degree of anisotropy. Special focus is given to the directional dependency of the permeability on isotropic and anisotropic geometries, considering the great impact of anisotropy on the laboratory evaluation of permeability data and the anisotropic nature of shale rocks. Simulation results, for the same value of porosity, clearly indicate the drastic improvement of permeability due to the reduction of specific surface area of pores and their height to width ratio. This suggests that rock matrix complexity has significant impact on permeability and should not be neglected while forming permeability formulations for porous media. Finally, the results of the apparent permeability, obtained by solving the gas kinetic equation, are taken into consideration to demonstrate the enhancement ratio, slip factor and their correlation with the aforementioned parameters. Semi-analytical expressions for intrinsic and apparent permeability, considering continuum and slip flow respectively, are derived. The proposed formulations, suitable for both isotropic and anisotropic structures, have the advantage of not entailing any numerical or experimental data as input.