水力裂缝与天然裂缝相互作用与影响

在非常规油气藏中,复杂裂缝网络的形成在很大程度上受水力裂缝与天然裂缝相互作用的影响。基于断裂力学理论,建立了水力裂缝与天然裂缝相互作用力学模型,分析天然裂缝介质系统中水力裂缝遭遇天然裂缝后的扩展形态。对于水力裂缝穿越天然裂缝的情况,给出了穿越角度;对于未穿越情况,给出天然裂缝张开闭合形态判别方法。通过数值计算研究了水平主应力差、逼近角、界面摩擦系数和裂缝净压力等因素的影响。结果表明,在高水平主应力差、高逼近角和高界面摩擦的条件下,水力裂缝倾向于穿越天然裂缝;在低水平主应力差、低逼近角和低界面摩擦的条件下,水力裂缝则更容易被捕获。同时,在水力裂缝内净压力越高,天然裂缝越容易张开。该模型为分析水力裂缝与天然裂缝相互作用过程以及水力压裂工程设计提供了依据。

The interaction between hydraulic fracture and natural fracture and influencing factors

In unconventional oil and gas reservoirs, the complexity of the fracture network system depends largely on the interaction between the hydraulic fracture and the natural fracture. Based on the fracture mechanics, a mechanical model of interaction between the hydraulic fracture and the natural fracture is established to study the hydraulic fracture geometry in naturally fractured media. In the case for the hydraulic fracture crossing the natural fracture, the fracture reinitiated angle is determined. In the case of no crossing, the model can judge whether the natural fracture remains close or stays open. Through numerical calculations, the influencing factors, such as horizontal principal stress difference, approaching angle, interface friction coefficient and fracture net pressure, are studied. Results show that under the circumstances of high horizontal principal stress difference, approaching angle and friction coefficient, the hydraulic fracture is more likely to cross the natural fracture. On the other hand, in the situation of low horizontal principal stress difference, intersection angle and friction coefficient, the hydraulic fracture tends to be captured by the natural fracture. Meanwhile, the higher the fracture net pressure, the more easily the fracture opens. This model provides a basis for hydraulic treatments in analyzing the interaction between the hydraulic fracture and the natural fracture.