Multiwell fracturing is a key technology for developing shale gas and shale oil reservoirs. In this study, a multiple planar 3D (PL3D) fracture simulator that can capture multiple thin layers was developed to examine the propagation of multiple fractures during multicluster fracturing in multiple horizontal wells. The simulator considers multiple thin layers in the vertical direction. The results of the model are validated against the analytical solution of a single radial fracture and the implicit level set algorithm (ILSA). Using the simulator, a series of numerical simulations based on the field case are performed to investigate the fracture propagation mechanism of multiwell fracturing. The completion sequence, well placement pattern, well spacing, and cluster spacing are investigated to optimize the treatment parameters. The effective fracture area is used to quantitatively describe the stimulation effect. The adaptability of the completion sequence and well placement pattern is also analysed from the perspective of “frac hits”. The results show that the completion sequence has a critical influence on the stimulation effect and fracture geometry. From the perspective of avoiding “frac-hit” fractures, fracturing the low-stress layer can form an “artificial stress barrier”, which slightly protects the well from interference from other fractures. The staggered well pattern is better than the stacked well pattern. Compared with the stacked pattern, the staggered pattern can reduce the overlap area of fractures by 80 %, which greatly reduces the probability of “frac-hits”. With increasing well spacing from 200 m to 500 m, the fracture area increases by 25 %, and the degree of uneven stimulation between the two pay zones also increases by 6 %. Considering that a small well spacing is prone to “frac hits”, a large well spacing leads to an unstimulated area between two wells, and a 350 m well spacing is optimal. The effective fracture area decreases slightly with increasing perforation cluster spacing, but the fracture geometry becomes much more regular. The results can be helpful for the field design of multiwell fracturing.

中文翻译：

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考虑垂直方向多薄层的多井压裂数值模拟


多井压裂是开发页岩气和页岩油储层的关键技术。在本研究中，开发了一种可以捕获多个薄层的多平面 3D （PL3D） 压裂模拟器，以检查多个水平井多集群压裂过程中多个裂缝的扩展。模拟器在垂直方向上考虑多个薄层。模型的结果根据单个桡骨骨折的解析解和隐式水平集算法 （ILSA） 进行了验证。利用该模拟器，基于现场案例进行了一系列数值模拟，研究了多井压裂的裂缝扩展机制。研究完井顺序、井放置模式、孔间距和集群间距以优化处理参数。有效裂缝面积用于定量描述刺激效果。还从 “压裂命中 ”的角度分析了完井序列和井放置模式的适应性。结果表明，完井序列对增产效应和裂缝几何形状有关键影响。从避免“压裂撞击”裂缝的角度来看，压裂低应力层可以形成“人工应力屏障”，稍微保护油井免受其他裂缝的干扰。交错孔模式优于堆叠孔模式。与堆叠模式相比，交错模式可以减少 80 % 的裂缝重叠面积，大大降低了“压裂打击”的概率。随着井距从 200 m 增加到 500 m，裂缝面积增加了 25 %，两个产层区之间的不均匀增产程度也增加了 6 %。 考虑到小井距容易出现“压裂冲击”，大井距会导致两口井之间出现无刺激区域，350 m 井距是最佳的。有效裂缝面积随着射孔簇间距的增加而略有减小，但裂缝几何形状变得更加规则。研究结果可为多井压裂的现场设计提供参考。