砂-页交互陆相页岩储层水力裂缝穿层扩展规律

Cross-layer propagation law of hydraulic fractures in continental shale reservoirs with sandstone-shale interaction

陆相页岩储层砂-页互层发育,层间岩石力学性质与地应力差异大,水力裂缝穿层扩展困难,导致压裂改造效果不佳。文中基于有限元+黏聚力单元法建立了砂-页交互陆相页岩储层三维水力裂缝穿层扩展数值模型,采用解析解与室内实验验证了模型的准确性,采用单因素和极差分析法开展算例研究,全面揭示了地质与工程因素对水力裂缝穿层扩展的影响规律。研究结果表明:高层间应力差、高层间抗张强度差、低层间弹性模量差、高隔层厚度均不利于水力裂缝穿层扩展,增大施工排量与压裂液黏度能有效提升水力裂缝穿层扩展能力;各因素影响程度的顺序为层间应力差>层间弹性模量差>层间抗张强度差>隔夹层厚度>注入排量>压裂液黏度。采用上述模型针对实例井开展施工参数设计,推荐单簇注入排量不低于2.5 m^(3)/min,前期施工压裂液黏度不低于20 mPa·s,现场应用效果良好,验证了模型的工程应用价值。

Due to the interbedded development of sandstone-shale in continental shale reservoirs,there are significant differences in rock mechanical properties and ground stress of the layers,making it difficult for hydraulic fractures to cross-layer propagation,resulting in poor fracturing stimulation effects.This article adopted the finite element+cohesive force element method to establish a three-dimensional numerical model of hydraulic fracture cross-layer propagation.The accuracy of the model was verified through analytical solution and indoor experiments,and single factor and range analysis methods were used to conduct case study,fully revealing the effect law of geological and engineering factors on hydraulic fracture cross-layer propagation.The research results indicate that high interlayer stress difference,high interlayer tensile strength difference,low interlayer elastic modulus difference and high interlayer thickness are not conductive to the cross-layer propagation of hydraulic fractures,and increasing the construction displacement and fracturing fluid viscosity can effectively improve the cross-layer propagation ability of hydraulic fractures.The order of the effect degree of each factor is as follows:interlayer stress difference,interlayer elastic modulus differences,interlayer tensile strength difference,interlayer thickness,injection displacement and fracturing fluid viscosity.The above model was used to conduct construction parameter design of example wells.It is recommended that the single cluster injection displacement should be no less than 2.5 m^(3)/min,and the fracturing viscosity during preliminary construction should be no less than 20 mPa·s.The on-site application effect is good,venifying the engineering application value of the model.