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中文摘要：
为探究页岩气藏水力压裂复杂裂缝网络的形成机理,开展了基于颗粒流的页岩破裂数值试验研究。根据页岩的岩石力学性质,采用并行PSO算法反演得到页岩颗粒细观力学参数,并基于PFC离散单元模型分别进行了预制2条裂纹下的巴西劈裂和水力劈裂数值试验,通过改变试验参数分析了裂纹相互作用对其扩展的影响。数值模拟发现：巴西劈裂试验预制裂纹夹角为30°和45°时,垂直裂纹扩展至倾斜裂纹时停止扩展转而从倾斜裂纹两端开裂并扩展,变形由弹性变形变为塑性变形;裂纹夹角为90°时,垂直裂纹贯穿水平裂纹,变形主要是弹性变形;水力劈裂试验中,预制裂纹夹角越小,倾斜裂纹越容易发生剪切破坏,垂直裂纹越趋于改变扩展方向,扩展路径越复杂。研究表明,裂纹倾角对页岩气藏水力压裂缝网的形态具有重要作用,岩体应变达到峰值后轴向应力-应变呈现先减小后增大的余弦波函数关系,且倾角越小压裂缝网越复杂。
英文摘要：
To discover the mechanism that generates complex fracture network in hydraulic fracturing of shale gas reservoirs,a numerical simulation was conducted hydraulic fracturing on shale cracking based on particle flow theory.Shale particle meso-mechanical parameters were retrieved by aparallel PSO algorithm with shale rock mechanical parameters.Brazilian tests and hydraulic fracturing tests with two preset cracks were carried out with the PFC discrete element model,with the next step that the effect of interaction between fractures on propagation was analyzed through varying test parameters.Numerical simulations demonstrated that when the preset crack was 30°or 45°inclined in the Brazilian test,the vertical crack turned into the preset crack and initiated from the sides of the preset crack.At that point,the stress-strain curve turned from elastic deformation to plastic deformation;when the preset crack was inclined 90°,the vertical crack propagated across the preset crack,and stress-strain curve demonstrated mainly elastic deformation.The smaller inclined angle of preset crack in the hydraulic fracturing test,and the easier preset crack shears,the more readily vertical crack changes its propagation direction,and further the more complicated propagation paths.The results demonstrated that the inclined angle of crack exerts significant influence on hydraulic fracture networks in shale gas reservoir;and after rock strain reaches is peak,the axial stress-strain curve decreases and then increases in a cosine wave relation.At that point,fracture networks become more complicated with decreasing inclined angle.
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