摘要
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
During the hydraulic fracturing stimulation of a perforated well, an improper perforation policy may cause limited communication between the well and the hydraulic fractures, such as a fracture initiating from one perforation might fail to linkup with adjacent perforations or multiple fractures might initiate from one perforation or adjacent perforations. Because the complexity of near-wellbore fractures may cause a premature screen-out, leading to a failing treatment, an optimized perforation policy is required to reduce the risk of limited communication. Many numerical and experimental studies have been conducted to optimize the perforation policy of the vertical or deviated wellbores with phasing angle of 0° or 90°, and the expected fracture geometry in these studies is longitudinal fractures that grow along the axis of the wellbore. However, fewer studies have been carried out on how the perforation policy influences the geometry of transverse vertical fractures from a cased and perforated horizontal well. In this work, a combined numerical and experimental study has been carried out to investigate the sensitivity of near-well fracture geometry of spiral-perforated horizontal wellbores. First, a laboratory-scale finite element model is built to give a stress distribution near the wellbore and perforations to obtain some understanding as to which perforations act as initiation sites. Following the principle of minimum fracture initiation pressure(FIP), the minimum perforation diameter and density value have been obtained to maintain a low FIP. Based on such parameter combinations, a series of physical simulation tests for concrete samples of different perforation parameters are conducted to study the influence of increasing perforation diameter or perforation density on the fracture geometry near wellbore. This also provides a way to test the effectiveness of traditional numerical methods on the optimization of perforation policy of the spiral-perforated horizontal wellbore. The results of the tests show tha
出处
《石油科学通报》
2017年第1期44-52,共9页
Petroleum Science Bulletin
基金
国家自然科学基金重点项目(51234006)
国家自然科学基金重大项目(51490651)联合资助
国家杰出青年科学基金项目(51325402)
关键词
水平井
螺旋射孔参数
有限元
水力压裂物理模拟
裂缝形态
破裂压力
horizontal wells
spiral perforation policy
finite element method
hydraulic fracturing physics tests
fracture geometry
fracture breakdown pressure
