Near-wellbore diverting fracturing (NWDF) can successfully generate new diverting fractures and dramatically enhance the stimulation effects for vertical wells. Investigating the fracture geometry and the injection pressure response is necessary for the candidate well selection and the stimulation effect evaluation. This work establishes a fully fluid–solid coupling model to simulate the process of NWDF under various parameter combinations, including the horizontal stress contrast, Young’s modulus, rock tensile strength, rock permeability, pore pressure, and injection rate. The model is verified against the reported experimental results. Moreover, the following key methods were applied in this study. Extended finite element method (XFEM) is applied to simulate the arbitrary fracture propagation path, which is a mesh-free simulation method; the initiation and propagation of the fracture tip elements are characterized by the cohesive zone model; a truss model is applied to simulate the propping effects of the proppants; a plug model is proposed to simulate the plugging effects of the tight plug. The simulation results show that the stimulation effects of NWDF can be improved by selecting the candidate well of low horizontal stress contrast, low Young’s modulus, low rock permeability, high rock tensile strength. However, the pore pressure has no impact on the stimulation effects of NWDF. Enhancing the fluid injection rate can improve the stimulation effects while the injection rate should be optimized for certain well. During the field operation of NWDF, a large difference between the peak value and the steady value of the diverting fracture injection pressure denotes a large curvature of the diverting fracture and a bad stimulation result. No obvious peak value of the diverting fracture injection pressure denotes a straight diverting fracture and a perfect stimulation result.

中文翻译：

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近井筒转向压裂裂缝几何特征及注入压力响应

近井筒转向压裂（NWDF）可以成功形成新的转向裂缝，显着提高直井增产效果。研究裂缝几何形状和注入压力响应对于候选井选择和增产效果评估是必要的。本工作建立了完全流固耦合模型来模拟各种参数组合下的 NWDF 过程，包括水平应力对比、杨氏模量、岩石抗拉强度、岩石渗透率、孔隙压力和注入速率。该模型根据报告的实验结果进行了验证。此外，本研究还应用了以下关键方法。采用扩展有限元法（XFEM）模拟任意裂缝扩展路径，是一种无网格模拟方法；断裂尖端单元的萌生和扩展由内聚区模型表征；采用桁架模型模拟支撑剂的支撑效果；提出了堵塞模型来模拟紧堵塞的堵塞效果。模拟结果表明，通过选择低水平应力对比、低杨氏模量、低渗透率、高岩石抗拉强度的候选井，可以提高NWDF的增产效果。但孔隙压力对NWDF的增产效果没有影响。提高注液量可以提高增产效果，但针对特定井应优化注液量。NWDF现场作业过程中，导流裂缝注入压力峰值与稳定值相差较大，说明导流裂缝曲率较大，改造效果较差。导流裂缝注入压力无明显峰值，表明导流裂缝平直，改造效果良好。