Abstract The simulation study of the effect of clay swelling on fracture generation and porosity change in shale rocks is of great significance for applying hydraulic fracturing in the development of shale reservoirs in the petroleum industry. However, previous simulations did not consider the heterogeneous characteristics of shales. Besides, it is not clear how the swelling stresses are distributed owing to swelling inside shales. In this paper, we employ a discrete element method (DEM) modeling, which is combined with the CT images and MATLAB coding, to predict the effect of clay swelling on fracture generation and porosity change in shales under stress anisotropy. We are able to successfully simulate the effect of clay swelling on fracture generation and porosity change in heterogeneous shales under stress anisotropy by employing the discrete element method (DEM) modeling. Clay content is the key factor in fracture generation and the resulted porosity change. For shales with high clay content, clay swelling has contributions to the recovery of shale's porosity. The von Mises stress maps show that the stress inside the model is highly anisotropic and the maximum effective stresses concentrate on the fractures' areas. The larger the pressure is applied to the sample, the larger the von Mises stress can be observed. Stress anisotropy is a positive factor in fracture generation in the process of water-shale interaction. The degree of the clay swelling and the heterogeneity of samples are two factors that could influence the results.

中文翻译：

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应力各向异性下粘土膨胀对页岩裂缝生成及孔隙度变化影响的模拟研究

摘要 黏土膨胀对页岩岩体裂缝生成及孔隙度变化影响的模拟研究，对水力压裂技术在石油工业页岩油藏开发中的应用具有重要意义。然而，以前的模拟没有考虑页岩的非均质特征。此外，由于页岩内部膨胀，膨胀应力如何分布尚不清楚。在本文中，我们采用离散元法 (DEM) 建模，结合 CT 图像和 MATLAB 编码，预测粘土膨胀对应力各向异性下页岩裂缝生成和孔隙度变化的影响。通过采用离散元方法 (DEM) 建模，我们能够成功模拟粘土膨胀对应力各向异性下非均质页岩中裂缝生成和孔隙度变化的影响。粘土含量是裂缝产生和孔隙度变化的关键因素。对于粘土含量高的页岩，粘土膨胀有助于页岩孔隙度的恢复。von Mises 应力图显示模型内部的应力是高度各向异性的，最大有效应力集中在裂缝区域。对样品施加的压力越大，可以观察到的 von Mises 应力就越大。应力各向异性是水-页岩相互作用过程中裂缝产生的积极因素。