页岩储层水力压裂裂缝扩展模拟进展

Simulation of Hydraulic Fracture Propagation in Shale Reservoir

页岩储层低孔低渗,水平井多级压裂、重复压裂和多井同步压裂为主要的增产措施,压裂缝扩展和展布对于页岩压裂设计和施工、裂缝监测、产能评价至关重要。对大量相关文献进行了调研和分析,得出以下结论:1水力压裂室内实验是评价页岩复杂裂缝形态最直接的方法,但难以真实地模拟实际储层条件下的水力压裂过程;2扩展有限元、边界元、非常规裂缝扩展模型、离散化缝网模型、混合有限元法及解析和半解析模型为页岩气常用的复杂裂缝扩展模拟方法,但各种方法都有其优缺点和适用性,需要进一步改进和完善才能真实地模拟页岩复杂裂缝扩展;3天然裂缝分布和水平主应力差共同决定页岩复杂裂缝网络的形成,天然裂缝与水平最大主应力方向角度越小、水平主应力差越大,复杂裂缝网络形成难度越大;天然裂缝与水平最大主应力方向的角度越大、水平主应力差越小,越容易形成复杂裂缝网络。研究结果可以为页岩储层缝网压裂裂缝扩展模拟和水力压裂优化设计提供借鉴。

As for low- porosity low- permeability shale gas reservoirs,multi- stage fracturing in horizontal wells,re- fracturing and multi- well simultaneous fracturing are major measures of stimulation. The propagation and distribution of fractures are of great significance to design,operation,monitoring,and productivity evaluation for shale fracturing. Through research and analysis on large amounts of literatures,following conclusions have been drawn:1laboratory experiment of hydraulic fracturing is the most direct approach to evaluate the complicated fracture patterns in shale,but it is hard to accurately simulate the process of hydraulic fracturing under real reservoir conditions;2finite element,boundary element or unconventional fracture propagation model,discretized fracture network model,composite finite element,and analytical and semi- analytical models are common methods to simulate complicated fracture propagation. All methods have their own pros and cons as well as applicability,and they need to be improved to precisely simulate complicated fracture propagation in shale;3the distribution of natural fractures and the difference of horizontal principal stress jointly decide the pattern of complicated fracture network. The smaller the directional angle between natural fracture and maximal horizontal principal stress is,the larger the difference of horizontal principal stress is,and the harder it is to form complicated fracture network; the larger the directional angle between natural fracture and maximal horizontal principal stress is,the smaller the difference of horizontal principal stress is,and the easier it is to form complicated fracture network. Research results can provide references for the simulation of fracture propagation in shale reservoir and design for hydraulic fracturing optimization.