A 3D multi-mechanistic model for predicting shale gas permeability
A 3D multi-mechanistic model for predicting shale gas permeability
复制标题
用于预测页岩气渗透率的 3D 多机制模型
DOI：
10.1016/j.jngse.2019.102913
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发表时间：
2019-08
影响因子：
--
通讯作者：
Li Yuyao
中科院分区：
文献类型：
--
作者：
Xu Shiqian;Feng Qihong;Wang Sen;Li Yuyao
页岩气藏由有机质、无机基质和天然裂缝等多种介质组成。甲烷在页岩体系中的流动具有多种机制，如努森扩散、表面扩散、吸附和相行为。然而，以往的研究没有同时考虑这些因素来预测页岩气的渗透率。在这里，我们开发了一个3D多机构模型来克服这一缺点。使用分类算法，我们首先划分了有机和无机孔的两种孔径分布(PSD)。然后分别测定了不同孔隙空间的气体渗透率。对于有机孔，我们考虑了努森扩散、表面扩散和吸附。对于无机孔隙，我们只考虑了努森扩散。这两种模型都考虑了真实气体效应和相态行为。在天然裂缝中，我们使用泊松定律来获得裂缝渗透率。然后，在嵌入式离散裂缝模型(EDFM)的基础上，综合考虑了天然裂缝、有机孔隙和无机孔隙三种孔隙类型对页岩气渗透率的影响。为了验证我们模型的可靠性，我们将结果与文献研究的数据进行了比较。通过敏感性分析，我们可以得出以下几个结论。天然裂缝对渗透率的影响最大，其次是无机孔隙和有机孔隙。由于天然裂缝的水平方向，水平方向的渗透率通常高于垂直方向。随着无机孔径的增大，渗透率也随之增加。随着有机孔径的增大，整体渗透率先下降后回升。相态效应和实际气体效应引起的总渗透率差异不大。该模型可作为预测页岩气渗透率的有效而全面的工具。
Shale gas reservoir consists of multiple media, including organic matter, inorganic matrix, and natural fracture. The flow of methane in shale system exhibits multiple mechanisms, such as Knudsen diffusion, surface diffusion, adsorption, and phase behavior. However, previous studies don't take these factors into account simultaneously to predict shale gas permeability. Here, we develop a 3D multi–mechanistic model to overcome this drawback. Using a classification algorithm, we first divide two pore size distributions (PSDs) of organic and inorganic pores. Then we measure the gas permeabilities of different pore spaces, respectively. Regarding organic pores, we consider Knudsen diffusion, surface diffusion, and adsorption. For inorganic pores, we only take Knudsen diffusion into account. Both models consider real gas effect and phase behavior. In natural fractures, we use Poiseuille law to obtain fracture permeability. After that, on the basis of embedded discrete fracture model (EDFM), we incorporate the effect of three pore types (natural fracture, organic and inorganic pores) to measure shale gas permeability. To verify the reliability of our model, we compare the result with the data from documented studies. Through sensitivity analysis, we can draw several conclusions as follows. Natural fracture has the greatest impact on permeability, followed by inorganic pore and organic pore. Owing to the horizontally oriented natural fractures, the permeability in horizontal direction is typically higher than that in vertical direction. As the inorganic pore size increases, permeability increases. While increasing organic pore size, the overall permeability will first drop and then pick up. The difference of the overall permeability caused by phase behavior and real gas effect is minor. Our proposed model can be used as an effective and comprehensive tool to predict shale gas permeability.
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