水力压裂中的应力阴影效应与数值计算

从岩石的细观非均质特性出发，采用岩石破裂失稳的渗流-应力-损伤耦合分析系统，设计了一系列的数值试验揭示水力裂缝间的应力阴影效应。试验条件下的研究结果表明：①应力阴影效应受水平应力差系数、注入孔间距、岩石非均质性、压裂顺序的影响，表现为排斥和吸引2种力学行为，体现在裂缝尖端应力伞面积、裂缝宽度和长度方面；②随着岩石均质度的提高，应力阴影效应对尖端应力伞的影响变弱，裂缝尖端应力伞的面积逐渐减小；③水平应力差较小时，井孔间距对应力阴影效应的贡献要大于远场应力；高水平应力差时，远场应力对“Stress shadow”的影响要强于井孔间距；④应力阴影效应伴随着裂缝的动态扩展而不断变化，裂缝尖端的应力伞面积和缝长具有很强的相关性，二者服从幂函数分布。通过这一研究，可以为水平井多裂缝射孔间距优化提供一定的理论依据。

Numerical Modeling of Stress Shadow Effect on Hydraulic Fracturing

From the aspect of meso-structure heterogeneity of gas shale,the seepage- stress-damage coupling code was used to investigate the stress shadow effect during hydraulic fracturing.The experimental results show that: (1)The stress shadow effect is affected by horizontal differential stress,injection spacing,heterogeneity and fracturing sequence.It displays repel and attract mechanical behaviors,which influences the stress-umbrella area,fracture length and width.(2)With the decrease of rock heterogeneity,the stress shadow effect has weaker influence on the stress-umbrella area,area becomes smaller gradually.(3)When the horizontal differential stress is smaller,influence of injection spacing on stress shadow competes over the far-field stress;with higher horizontal differential stress,influence of far-field stress on stress shadow competes injection spacing.(4)The stress shadow effect displays dynamic variation with the evolution of hydraulic fractures.There is strong correlation between stress umbrella area and fracture length,and they obeyed power function.Through this research,it can provide certain theatrical basis for horizontal well spacing and multiple perforation spacing optimization.