压裂中水力裂缝穿过天然裂缝判断准则

New criteria for hydraulic fracture crossing natural fractures

为准确预测水力压裂过程中水力裂缝是否会穿过天然裂缝及其穿出方向,基于弹性力学理论,建立了水力裂缝穿过天然裂缝的判断准则,并给出了水力裂缝穿出天然裂缝时穿出角度的计算方法。计算结果表明:在给定逼近角下对应有确定的水力裂缝穿过天然裂缝所需的水平主应力比值范围,超过或低于这个范围水力裂缝将不能穿过天然裂缝;高逼近角及高水平主应力比值下水力裂缝易直接穿过天然裂缝;在相同逼近角下,水平主应力比值越大,穿出方向总是倾向于靠近增大的水平主应力方向。

The complexity of a hydraulic fracture network depends on the behaviors of induced hydraulic fractures as they intersect natural fractures, so it is important to understand the mechanism of fracture intersection under particular field conditions of in-situ stresses, rock and natural fracture properties. An accurate criterion for the fracture propagation across natural fractures is established, and the direction of the reinitiated fracture is also studied. The results show that for a given approaching angle there exits a certain range of stress ration when crossing occurs, beyond this range crossing will not occur. Under high horizontal differential principle stress and approaching angle, hydraulic fracture is more likely to cross the natural fracture. As the stress ration increases, the direciton of reinitiated fracture draws closer to the direction of the incremental principle stress. This new criterion can be applied in the general analysis of fracture network and simulation of numerical fracture network.