【作者】 李勇；

【导师】 杨焕强；

【作者基本信息】 长江大学 ， 油气井工程， 2025， 硕士

【摘要】 本文针对川南地区的深层页岩储层非连续面力学参数表征方法欠缺,缝网形成机理研究尚不完善的问题展开研究。综合试验研究、理论分析和数值模拟,形成深层页岩储层非连续面力学参数表征方法,探究高应力状态下多簇裂缝干扰机理,明确深层页岩储层多层理与多簇裂缝交互扩展规律,揭示深层页岩储层复杂缝网形成机理。分析影响深层页岩储层缝网形成的主控因素,优化压裂施工参数,对深层页岩气缝网改造具有参考意义。取川南地区页岩露头,进行了巴西劈裂和三轴压缩试验,获取天然页岩基础力学参数,探究了不同层理角度层理面对整体岩石破坏行为的影响。层理角度显著影响岩石强度和裂缝扩展形式,60°时层理页岩的抗拉和抗压强度最大,围压显著影响裂缝破坏形态,围压增大,岩石难以发生剪切破坏,裂纹形态也越简单。利用三点弯曲加载系统结合数字图像法不仅计算了不同层理角度下岩石的断裂韧性,同时观察到层理角90°时裂缝沿层理面破坏时以拉张破坏为主,结合加载数据获取了层理面的关键力学参数——界面拉伸刚度。基于内聚力单元法,结合流固耦合方程,缝内流动方程,借助管流单元(FP3D2)和管流连接单元(FPC3D2),模拟了多裂缝、多层理页岩中的射孔摩阻压降和流量动态分配问题。建立了一系列多层页岩中多裂缝扩展的三维有限元模型,揭示了裂缝与层理之间的干扰机理,探索了多条水力裂缝和层理裂缝的传播规律。研究表明,层理面的开启同样会产生诱导应力,水力裂缝产生的诱导应力集中于水力裂缝基部,而层理缝产生的诱导应力分布在整个层理缝扩展平面,该诱导应力对层理缝的开启至关重要。对不同的层理结构参数进行了模拟,裂缝网络的形态受到层理平面性质的显著影响。一方面,层理平面的分流作用限制了水力裂缝的垂直扩展。另一方面,上部层理平面的张开受阻于已开启层理缝的诱导应力和垂向地应力的压实作用。9组数值模拟结果表明,层理强度影响层理平面的开度和连通性,层理间距影响上部层理平面的开度,而水力裂缝的垂直扩展受层理密度的影响。针对深层页岩储层高应力差的特点,分别探究了高水平应力差和高垂向应力差对裂缝扩展的影响,水平应力差越大,水力裂缝穿层时所需的注入压力增大,表明裂缝纵向扩展需要更大的水力能量,水力缝高受限制。垂向应力差越大,由于垂向上的压实作用,层理弱面开启阻力越大,因此高垂向应力差下的裂缝形态简单,难以沟通弱面形成缝网结构。对同时处于高水平应力差和高垂向应力差的压裂工况进行了施工参数优选,结果表明:施工时采用交替排量注入,增大簇间距(10m),增加射孔簇数(5～7簇),增大压裂液黏度(>10m Pa·s),可以在增大水力裂缝与层理面沟通面积的同时突破缝高的限制,改善压裂效果。更多还原

【Abstract】 This study addresses the challenges of insufficient characterization methods for mechanical parameters of discontinuities and incomplete understanding of fracture network formation mechanisms in deep shale reservoirs of southern Sichuan Basin.Through integrated experimental research,theoretical analysis,and numerical simulation,we develop a mechanical parameter characterization methodology for discontinuities in deep shale reservoirs.The investigation focuses on three key aspects:(1)multi-cluster fracture interference mechanisms under high-stress conditions,(2)interactive propagation patterns between multi-layer bedding and multi-cluster fractures,and(3)fundamental mechanisms governing complex fracture network formation.Furthermore,the research identifies primary controlling factors influencing fracture network development and optimizes fracturing stimulation parameters,providing valuable insights for effective reservoir modification in deep shale gas formations.Shale outcrops from the southern Sichuan Basin were subjected to Brazilian splitting tests and triaxial compression tests to obtain fundamental mechanical parameters of natural shale and investigate the influence of bedding plane angles on rock failure behavior.Results demonstrate that bedding plane angle exerts a significant control on rock strength and fracture propagation patterns.Peak tensile and compressive strengths occur at a bedding angle of 60°.Confining pressure critically affects failure modes:higher confining pressures inhibit shear failure and simplify crack morphology.Using a three-point bending system combined with digital image correlation(DIC),fracture toughness was quantified across varying bedding angles.At 90°,tensile-dominated failure along bedding planes was observed,and the interface tensile stiffness—a critical mechanical parameter of bedding planes—was derived from loading data.A three-dimensional finite element modeling framework was established using the cohesive zone method integrated with fluid-solid coupling equations and fracture flow equations,incorporating pipe flow elements(FP3D2)and pipe flow connector elements(FPC3D2),to simulate perforation friction pressure drop and dynamic fluid distribution in multi-fractured,multi-bedded shale.The study revealed interference mechanisms between fractures and bedding planes,as well as propagation patterns of hydraulic fractures and bedding fractures.Results indicate that bedding plane activation generates induced stresses:hydraulic fracture-induced stresses concentrate near the fracture base,while bedding fracture-induced stresses distribute across the propagation plane,critically controlling bedding fracture initiation.Numerical simulations of varying bedding structure parameters demonstrate that fracture network geometry is strongly influenced by bedding plane properties.First,flow diversion through bedding planes restricts vertical hydraulic fracture growth.Second,upper bedding plane opening is constrained by induced stresses from activated bedding fractures and compaction from vertical in-situ stress.Nine numerical cases demonstrate that bedding strength governs bedding plane aperture and connectivity,bedding spacing affects upper bedding plane aperture,and vertical hydraulic fracture propagation is controlled by bedding density.This study investigates fracture propagation mechanisms under high-stress contrast conditions in deep shale reservoirs.Enhanced horizontal stress contrast increases injection pressure required for fracture vertical penetration,indicating greater hydraulic energy demand for height growth with constrained fracture elevation.Elevated vertical stress contrast amplifies bedding plane activation resistance due to vertical compaction effects,resulting in simplified fracture geometries and impaired fracture network development through bedding weaknesses.Operational parameter optimization for combined high horizontal/vertical stress contrast scenarios demonstrates that alternating-rate injection protocols with reduced cluster spacing(10m),increased perforation clusters(5-7 clusters),and elevated fracturing fluid viscosity(>10 m Pa·s)effectively enhance bedding plane interaction area while overcoming height constraints.This approach achieves improved fracture connectivity and stimulation effectiveness in complex stress environments.更多还原