泥页岩构造裂缝形成演化模式——以四川盆地东部泥页岩为例

以四川盆地东部泥页岩为例，在野外地质研究基础上，运用岩石力学实验、光弹物理模拟和有限元数学模拟等手段，结合水力压裂开发统计资料，开展了泥页岩构造裂缝形成演化研究。研究认为，泥页岩沉积韵律发育，先存薄弱面密集，不均质性强烈。泥页岩层面是裂缝优先发育的结构面，控制了裂缝的形成和发育演化特点。在构造变形过程中，当遇到泥页岩层面时，应力方向发生调整，压应力趋向平行薄弱面，张应力趋向垂直薄弱面，从而引起薄弱面开启，优先发育顺层缝。当顺层缝不足以调节构造变形时，发育切层缝。不同构造变形部位泥页岩裂缝分布特征差异性明显，可以划分为背斜顶部高角度缝发育区、切层缝向顺层缝扩展区、滑移转换区、切层缝向顺层缝爬移区和向斜底部高角度缝发育区5个区。同时提出在针对构造高点勘探时，多套盖层的叠置是有利条件。在针对储层甜点勘探时，裂缝发育和扩展是关键要素。

A discussion on formation and evolutionary pattern of shale structural fracture:A case study of shale in western Sichuan Basin

Taking the shale in the eastern Sichuan Basin as examples,we studied the formation and evolutionary patterns of structural fractures in shale through field observation,rock mechanics experiment,physical simulation of photo elastic and finite element simulation in combination with statistical data of development via hydraulic fracturing. It is revealed that the shale has rich deposit rhythm,pre-existing weak surfaces and strong heterogeneity. Shale bedding is the preferred structure surface for fracture development and controls the formation and evolutionary characteristics; Stress will adjust its direction when encountering shale bedding during structural deformation. The compressive stress tends to parallel weak surface,while the tension stress tends to be vertical to weak surface,which leads to weak plane opening and preferred development bedding-parallel fractures. Bedding-crossing fractures would develop when the bedding-parallel fractures are not enough to accommodate tectonic deformation. Characteristics of shale fracture distribution have sharp distinction in different locations of tectonic deformation which can be divided into five areas such as anticlinal top high angle fractures,extension of bedding-crossing fracture to bedding-parallel fracture,slip conversion,bedding-crossing fracture climbing to bedding-parallel fracture and synclinal bottom high angle fractures. It is proposed that areas with multiple sets of cap rocks overlapping is a favorable condition for exploration on structural highs,while the development and expansion of fractures is the key factor for exploration in sweet spots.