Shale gas reservoirs often need hydraulic fracturing treatments to create complex fracture network to enhance production. Frictional and cemented natural fractures are often contained in shale formations. The interactions between the hydraulic fractures and these two types of pre-existing natural fractures are different. In this study, we established a two-dimensional fluid-solid coupled hydraulic fracturing model using the extended finite element method (XFEM) to simulate the interactions between hydraulic fractures and natural fractures, and further the formation of fracture network. The results show that when a hydraulic fracture intersects with a natural fracture, the hydraulic fracture may be arrested and propagate along the direction of natural fracture, or cross the natural fracture without being affected. For the frictional natural fractures, the intersection angle, frictional coefficient, stress anisotropy and rock tensile strength have a significant influence on creating fracture network. It is found that decreasing stress difference and interfacial friction, or increasing rock tensile strength may lead to more complex fracture network. For the cemented natural fractures, the intersection angle and the ratio of cement toughness and rock toughness play critical roles in the creation of fracture network. Smaller intersection angle and cement toughness of NFs and larger rock fracture toughness often lead to more complex fracture network. In addition, for the same initial geometrical configuration of natural fractures, hydraulic fracturing often leads to more complex fracture network in formations containing frictional natural fractures compared with formations containing cemented natural fractures. These findings offer new insights into the nature and degree of fracture complexity, helping to optimize hydraulic fracturing design in shale gas reservoirs.

页岩气储层经常需要水力压裂处理，以形成复杂的裂缝网络，以提高产量。页岩地层通常包含摩擦性和胶结性天然裂缝。水力压裂与这两种既存的自然压裂之间的相互作用是不同的。在这项研究中，我们使用扩展有限元方法（XFEM）建立了二维流固耦合水力压裂模型，以模拟水力压裂与自然压裂之间的相互作用，并进一步建立裂缝网络。结果表明，当水力裂缝与自然裂缝相交时，水力裂缝可能会被阻止并沿自然裂缝的方向传播，或横越自然裂缝而不受影响。对于摩擦性天然裂缝，相交角，摩擦系数，应力各向异性和岩石抗拉强度对形成裂缝网络有重要影响。发现减小应力差和界面摩擦，或增加岩石抗拉强度可能导致更复杂的断裂网络。对于胶合天然裂缝，相交角和水泥韧度/岩石韧度之比在裂缝网络的形成中起着关键作用。NFs的交角和水泥韧性较小，而岩石的断裂韧性较大，通常会导致断裂网络更加复杂。此外，对于天然裂缝的相同初始几何构型，与包含胶结天然裂缝的地层相比，水力压裂通常会导致包含摩擦性天然裂缝的地层中更复杂的裂缝网络。这些发现为裂缝复杂性的性质和程度提供了新的见解，有助于优化页岩气储层的水力压裂设计。