页岩储层压裂缝网模拟研究进展

页岩储层压裂缝网表征是现阶段页岩气开采面临的主要难题之一，因此在了解缝网扩展主控因素的基础上，选择合理的、具有优势的实验（试验）和模拟方法是有效推进页岩开采的重要环节。通过调研大量页岩压裂缝网研究的矿场试验、室内实验以及数值模拟方法及成果，尤其对比、分析了各种数值模拟方法的发展和现状，展望了数值模拟技术的发展方向，并系统归纳了影响缝网的主控因素及其影响机理，得出以下认识：①页岩储层压裂缝网数值模拟方法中，基于有限元模型的扩展有限元模型、在离散裂缝网络模型基础上发展的非常规裂缝网络模型以及从分形理论出发的分形裂缝网模型在页岩复杂缝网模拟中体现了优越性和可持续发展性；②裂缝扩展在真实地层中主要受控于缝内压力、岩石脆性、地应力、层理和天然裂缝，页岩储层岩石脆性较强、层理发育、天然裂缝广泛分布，极大地增加了缝网复杂程度，裂缝扩展整体上主要是以上因素共同作用的结果；③现阶段复杂裂缝网络模拟方法基于边界元、有限元、离散元、解析法，由于每种方法的特征和适用性不同，融合不同数值方法的建模、求解更有模拟潜力。

Research progress on fracture network simulation in shale reservoirs

The shale reservoir fracture network charac-terization is one of the most important issues of shale gas exploitation at the present stage.On the basis of the main controlling factors of fracture network expansion,it is an important link to select reasonable and advantageous experimental(test) and simulation methods to effectively promote shale exploitation.Through the investigation of a large number of field tests,laboratory experiments and numerical simulations,and research results of shale fracture network,the development and status quo of various numerical simulation methods are analyzed,the development direction of numerical simulation is predicted,and main controlling factors and influencing mechanism of fracture network are systematically summarized.Based on the above research,the following observations are obtained:A.Three numerical models of fracture network in shale reservoirs embody advantages and sustainable development:extended finite element model based on finite element model,unconventional fracture network model based on discrete fracture network model,and fractal fracture network model based on fractal theory; B.The fracture propagation in real strata is mainly controlled by fracture pressure,rock brittleness,in-situ stress,bedding,and natural fractures.Shale reservoir rocks are characterized by strong brittleness,well-developed bedding,and widely-distributed natural fractures,which greatly increases the complexity of fracture networks.On the whole,the fracture propagation is a result of the combined action of the above factors; C.At present,simulation methods of complex fracture network are based on different methods such as boundary element method,finite element method,discrete element method,and analytical method.Each method is suitable for a specific situation,so numerical methods for different situations are needed.