Natural fractures in tight sandstone formation play a significant role in fracture network generation during hydraulic fracturing. This work presents an experimental model of tight sandstone with closed cemented preexisting fractures. The influence of closed cemented fractures’ (CCF) directions on the propagation behavior of hydraulic fracture (HF) is studied based on the hydraulic fracturing experiment. A field-scaled numerical model used to simulate the propagation of HF is established based on the flow-stress-damage (FSD) coupled method. This model contains the discrete fracture network (DFN) generated by the Monte-Carlo method and is used to investigate the effects of CCFs’ distribution, CCFs’ strength, and in-situ stress anisotropy, injection rate, and fluid viscosity on the propagation behavior of fracture network. The results show that the distribution direction of CCFs is critical for the formation of complex HFs. When the angle between the horizontal maximum principal stress direction and the CCFs is in the range of 30° to 60°, the HF network is the most complex. There are many kinds of compound fracture propagation patterns, such as crossing, branching, and deflection. The increase of CCFs’ strength is not conducive to the generation of branched and deflected fractures. When the in-situ stress difference ranges from 3 MPa to 6 MPa, the HF network’s complexity and propagation range can be guaranteed simultaneously. The increase in the injection rate will promote the formation of the complex HF network. The proper increase of fracturing fluid viscosity can promote HF’s propagation. However, when the viscosity is too high, the complex HFs only appear around the wellbore. The research results can provide new insights for the hydraulic fracturing optimization design of naturally fractured tight sandstone formation.

中文翻译：

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封闭胶结天然裂缝致密砂岩地层水力裂缝网络扩展行为研究

致密砂岩地层中的天然裂缝在水力压裂过程中对裂缝网络的生成起着重要作用。这项工作提出了一个具有封闭胶结预先存在裂缝的致密砂岩的实验模型。在水力压裂实验的基础上，研究了闭合胶结裂缝（CCF）方向对水力裂缝（HF）扩展行为的影响。基于流动-应力-损伤（FSD）耦合方法建立了用于模拟高频传播的场尺度数值模型。该模型包含由蒙特卡罗方法生成的离散裂缝网络 (DFN)，用于研究 CCF 的分布、CCF 的强度以及地应力各向异性、注入速率和流体粘度对传播行为的影响裂隙网络。结果表明，CCFs的分布方向对于复杂HFs的形成至关重要。当水平最大主应力方向与 CCF 的夹角在 30°～60° 范围内时，HF 网络最为复杂。复合裂缝扩展方式有交叉、分支、偏转等多种。CCFs强度的增加不利于分支和偏转裂缝的产生。当地应力差在 3 MPa 到 6 MPa 范围内时，可以同时保证高频网络的复杂性和传播范围。注入速率的增加将促进复杂的HF网络的形成。适当增加压裂液粘度可以促进HF的传播。但是，当粘度过高时，复杂的 HF 仅出现在井筒周围。研究成果可为天然裂缝性致密砂岩地层水力压裂优化设计提供新思路。