重复压裂前诱导应力影响新裂缝转向规律

Study of fracture reorientation caused by induced stress before re-fracturing

随着重复压裂技术现场应用的日趋成熟,如何产生不同于原裂缝走向的转向新裂缝成为目前重复压裂技术研究的热点问题。由于新裂缝的扩展方向主要由井周应力分布情况控制,重复压裂前初次裂缝、油井生产以及注水影响等因素产生的诱导应力是影响新裂缝形态的主要因素。应用多物理场耦合软件COMSOL建立了重复压裂井有限元模型,分析了重复压裂裂缝转向的机理和影响因素;建立了注水开发区块模型,研究了注水开发中注入水诱导应力的分布规律,以及注水量、注采井网分布等因素对新裂缝转向的影响。研究结果表明:裂缝转向受储层应力状态、油井生产情况和初次裂缝长等因素影响明显;注水井周边会产生应力集中,且在一定的井距下会影响新裂缝转向规律。此研究可以应用于预测重复压裂效果,优化重复压裂的选井选层,并指导现场重复压裂方案设计。

With mature refracturing technology application, how to create a new fracture that has different orientation from the original fracture is becoming a hot issue in the current research of refracturing. As the direction of the new cracks is mainly controlled by the stress distribution near the wellbore, and the induced stress caused by the initial fractures, the production of oil wells and the influence of water injection are the main factors affecting the new fracture morphology. The finite element model of refracturing well was established by COMSOL, and the mechanism and influencing factors of fracture reoriented were analyzed. The water injection block model was established to study the distribution of water induced stress, and the influence of injection volume, injection and distribution network and other factors on fracture morphology. The results of simulation show that the fracture orientation is affected relatively large by the stress state of the reservoir, the oil well production and the initial crack length. Stress concentration will occur around the injection wells, and in a certain distance will affect the reorientation of the new fracture. This study can be applied to predict the refracturing effect, optimize the selection of wells, and guide the design of refracturing.