Impact of geomechanical heterogeneity on multiple hydraulic fracture propagation
Impact of geomechanical heterogeneity on multiple hydraulic fracture propagation
复制标题
地质力学非均质性对多处水力裂缝扩展的影响
DOI：
10.1093/jge/gxab058
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发表时间：
2021
影响因子：
1.4
通讯作者：
Xiaohu Dong
中科院分区：
文献类型：
--
作者：
Yunlin Gao;Huiqing Liu;Chunsheng Pu;Huiying Tang;Kun Yang;Xiaohu Dong
为了从页岩气藏中提取更多的气体，水力压裂裂缝之间的间距应该被做得更小，导致显著的应力阴影效应。大多数关于应力阴影效应的研究都是基于岩石性质均匀性的假设。然而，页岩储层具有很强的非均质性，用均质模型计算的结果与实际情况存在较大差异。在这项工作中进行了一系列的案例研究，以了解力学非均匀性对多裂缝扩展的影响。采用扩展有限元法模拟了裂纹扩展过程。进行连续高斯模拟以产生地质力学性质的不均匀分布。根据模拟结果，断裂扩展的难度与杨氏模量和泊松比呈负相关，与抗拉强度呈正相关。当多个裂缝中的每一个在具有不同力学性质的均匀区域中扩展时，裂缝的最终几何形状类似于均匀条件。当岩石参数为垂直于裂缝扩展方向的随机场或非均质时，裂缝将不再以井筒为对称中心。基于随机场中裂缝扩展的分析，弹性参数的微小变化可导致多条裂缝的不对称扩展。此外，水力裂缝的不对称扩展对泊松比的非均匀性比杨氏模量更敏感。这项研究强调了考虑地质力学非均匀性的重要性，并提供了一些有意义的建议，水力压裂设计。
To extract more gas from shale gas reservoirs, the spacing among hydraulic fractures should be made smaller, resulting in a significant stress shadow effect. Most studies regarding the stress shadow effect are based on the assumption of homogeneity in rock properties. However, strong heterogeneity has been observed in shale reservoirs, and the results obtained with homogeneous models can be different from practical situations. A series of case studies have been conducted in this work to understand the effects of mechanical heterogeneity on multiple fracture propagation. Fracture propagation was simulated using the extended finite element method. A sequential Gaussian simulation was performed to generate a heterogeneous distribution of geomechanical properties. According to the simulation results, the difficulty of fracture propagation is negatively correlated with the Young's modulus and Poisson's ratio, and positively correlated with tensile strength. When each of the multiple fractures propagates in a homogeneous area with different mechanical properties, the final geometry of the fracture is similar to homogeneous conditions. When the rock parameter is a random field or heterogeneity perpendicular to the propagation direction of fracture, the fracture will no longer take the wellbore as the center of symmetry. Based on the analysis of fracture propagation in random fields, a small variance of elastic parameters can result in asymmetrical propagation of multiple fractures. Moreover, the asymmetrical propagation of hydraulic fractures is more sensitive to the heterogeneity of Poisson's ratio than Young's modulus. This study emphasises the importance of considering geomechanical heterogeneity and provides some meaningful suggestions regarding hydraulic fracturing designs.