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射孔井压裂施工中,射孔参数选择不当易造成水力裂缝无法沟通尽量多的射孔孔眼或造成多缝起裂,引起近井筒复杂裂缝状态,从而降低井筒与水力裂缝的沟通性,影响后续支撑剂填加作业,导致压裂失败。射孔参数优化对降低破裂压力以及避免近井筒裂缝复杂性具有重要意义。前人多采用数值模拟与室内物理模拟方法针对直井或斜井条件下的0°或180°相位射孔参数进行优化,所研究的裂缝形态多为沿井眼轴向扩展的水力裂缝,而对于水平井螺旋射孔条件下横向水力裂缝的扩展规律以及相应射孔参数优化方面的研究较少。本文采用数值计算与物理模拟相结合的方法研究水平井螺旋射孔参数对近井筒裂缝形态的影响规律,建立实验室尺寸的三维水平井螺旋射孔有限元模型,分析了不同孔眼处起裂压力的分布规律,并基于最小起裂压力原则,得到能有效降低模型起裂压力的最小孔径与孔密参数。在此射孔参数组合基础上,为研究继续增加孔密或孔径对水平井水力裂缝形态的影响,也为验证有限元方法在水平井螺旋射孔参数优化方面的有效性,设计了不同螺旋射孔参数的混凝土试样进行真三轴水力压裂物理模拟。实验结果显示,采用传统有限元方法对水平井螺旋射孔参数进行优化具有局限性,其优化参数条件下,孔眼间水力裂缝连接性较差,从单个孔眼起裂的水力裂缝倾向独立扩展,无法形成沟通多个孔眼的主裂缝面以增强水力裂缝与井筒的连通性;在有限元优化结果基础上增加射孔孔径,一定程度上增强了孔眼间水力裂缝的连接,但整体依然存在裂缝重叠区域,且破裂压力也较高;相比于增加孔径,增加射孔密度更能促进射孔间水力裂缝的相互连接,形成沟通多个孔眼的主裂缝面,在保证破裂压力较低的情况下降低了近井筒裂缝的复杂性。研究成果可为现场作业提供指导,由于射孔孔径与射孔密度均会对套管强度产生影响,现场进行射孔参数优化时,在确保套管强度条件下,应优先考虑增加射孔密度以降低近井筒裂缝复杂性,便于后续填加支撑剂作业。
In perforating well fracturing, improper perforation parameters can easily lead to hydraulic fractures unable to communicate as much perforation holes or multiple fracture initiation, causing complex fractures near the wellbore, thereby reducing the communication between the wellbore and the hydraulic fractures and affecting Follow-up proppant filling operation, resulting in fracturing failure. Optimization of the perforation parameters is of great importance to reduce the fracture pressure and to avoid the complexity of the near-wellbore fracture. In the past, the numerical simulation and in-house physical simulation methods were mostly used to optimize the 0 ° or 180 ° phase perforation parameters under straight or inclined well conditions. Most of the fractures studied are hydraulic fractures extending axially along the borehole, There are few researches on the propagation of transverse hydraulic fractures and the optimization of corresponding perforation parameters under horizontal well perforating. In this paper, the effect of horizontal helical perforation parameters on the shape of fractures near the wellbore was studied by means of numerical computation combined with physical simulation. A three-dimensional horizontal helical perforation finite element model was established and analyzed. Based on the principle of minimum cracking pressure, the minimum aperture and hole density parameters that can effectively reduce the cracking pressure of the model are obtained. Based on this combination of perforation parameters, in order to study the influence of hole density or hole diameter on the hydraulic fractures of horizontal wells, and to verify the effectiveness of the finite element method in horizontal well perforation parameters optimization, Hole parameters of concrete samples for true triaxial hydraulic fracturing physical simulation. The experimental results show that the traditional finite element method has some limitations on the optimization of horizontal well perforating parameters. Under the optimal conditions, the hydraulic fracture connectivity between holes is poor, and the tendency of hydraulic fractures from a single hole expands independently, Forming the main fracture surface communicating with a plurality of holes to enhance the connectivity between the hydraulic fracture and the wellbore; increasing the perforation aperture based on the optimization results of the finite element, to some extent, enhancing the connection of hydraulic fractures among the perforations, but the whole area of the fracture overlap , And the fracture pressure is also higher. Compared with increasing the pore diameter, increasing the perforation density can further promote the interconnection of the hydraulic fractures between the perforations to form a main fracture surface that communicates with a plurality of perforations, and decreases when the fracture pressure is low Near the wellbore cracks the complexity. The research results can provide guidance for on-site operation. Because the perforating aperture and perforation density will affect the casing strength, when perforation parameters are optimized on site, under the condition of ensuring casing strength, the perforation density should be given priority Reduce the complexity of near-wellbore cracks and facilitate the subsequent filling of proppant operations.