基于离散元方法的层理发育地层水力裂缝扩展规律

Hydraulic Fractures Propagation in Bedding Developed Stratum Based on Distinct Element Method

层理发育是页岩储层的典型特征,水力裂缝能否穿过层理面继续扩展决定了裂缝形态的复杂程度,其中层理强度是影响水力裂缝穿层行为的关键因素。为了探究层理强度对水力裂缝穿层行为的影响,采用块体离散元方法,分别计算了层理面的抗剪强度(黏聚力)和抗拉强度对水力裂缝在层状地层内扩展行为的影响。结果表明,水力裂缝遇到水平层理后的形态可分为转向层理面扩展和继续竖向扩展两种类型。层理面强度对水力裂缝的穿层能力具有显著影响,当层理面的抗拉强度和抗剪强度均较低时,水力裂缝的穿层能力差,水力裂缝不能穿过层理;当层理面的抗拉强度和抗剪强度均较高时,水力裂缝的穿层能力增强,水力裂缝穿过层理面扩展;当层理面的某一个强度较低时(抗拉或抗剪),则低强度因素成为主控因素,另一强度参数的增加不会改变水力裂缝的穿层能力。厘清了层理强度对水力裂缝穿层行为的影响,对层理发育地层的水力压裂施工具有重要的理论指导意义。

The bedding is relatively developed in shale reservoir.And the bedding has an important influence on the propagation of hydraulic fractures.In order to explore the influence of the deformation parameters and bedding strength on the behavior of hydraulic fractures penetrating through the stratum,shear strength and tensile strength of the bedding plane were calculated by the block discrete element method.The results show that the hydraulic fractures behavior can be divided into two types after encountering horizontal bedding plane.The bedding-penetrating ability of hydraulic fractures was controlled by the strength of bedding plane.When the tensile strength and shear strength of the bedding plane are both low,the penetration ability of hydraulic fractures is poor,and hydraulic fractures cannot penetrate the bedding plane.When the tensile strength and shear strength of the bedding plane are both high,the bedding-penetration ability of the hydraulic fracture is enhanced,and the hydraulic fracture propagates through the bedding plane.When one of strength of the bedding plane is low(tensile or shear),it becomes the main control factor,and the increase of another strength will not change the bedding-penetration ability of hydraulic fractures.The research clarifies the influence of bedding strength on the hydraulic fracturing behavior,which has important theoretical significance for the hydraulic fracturing construction of the bedding developed formation.