174 / 2023-07-14 16:53:40

层内构造解析对页岩气甜点和钻井施工的指导意义

四川盆地南部,页岩气,层内构造,研究方法,研究理论

川南地区是我国海相页岩气重点开发区，其主要产层为五峰组-龙马溪组。然而，该区页岩气仍面临着勘探甜点认识不清、钻井工程复杂等技术瓶颈。五峰组-龙马溪组是一套重要的区域滑脱层，内部的层内构造与区域构造之间具有强烈的不协调性。以往常将页岩层作为区域软弱层进行宏观研究，对其本身层内构造研究甚少。当页岩气产层内发育层内褶皱、断裂及配套裂缝带等复杂构造体系时，勘探开发生产难度将大大增加。因此，理清这些层内复杂构造的样式、类型、展布规律以及与区域构造的成生联系，将促进页岩气的高效、安全和可持续开发。

首先，通过野外地质调查、构造演化史研究和构造物理模拟实验，为层内构造样式地震精细解析提供地质理论约束：（1）对页岩目的层上覆、下伏岩层的褶皱-断裂成生机制进行解析，搞清层内构造与区域构造之间的成生联系；（2）分析川南地区构造-沉积的成生演化史，理清一系列构造行迹的形成过程与动力学成生机制；（3）搭建仿真模型，确定边界条件，开展构造物理模拟实验，理清断层变位、褶皱变形在强硬岩层与软弱层之间转变关系。

在上述地质约束基础上，对川南地区三维地震数据体进行倾角、方位角、曲率、混沌、方差、均方差振幅、反射强度、广义谱分解、蚂蚁体追踪等多种属性提取，运用断层相关褶皱、层间剪切滑动、平面走滑体系等相关构造地质学理论，对页岩层内潜在的复杂微幅构造进行精细刻画，理清褶皱-断裂-裂缝的构造配置关系。进而厘定出2类有利页岩层内构造：层内剪切构造和层内断层相关褶皱远端构造；及3类不利页岩层内构造：层内断层相关褶皱近端、层内走滑伴生构造和褶皱核部拉张构造；并阐释了不同的层内构造类型下，裂缝带的发育、配套模式。分析结果在多个钻井平台进行了验证和相关预测，已取得可喜成效。

本研究首次对川南地区页岩层内构造进行了详细厘定和刻画，其研究成果对页岩气甜点预测、钻井布置、随钻导向和工程风险防范提供科学支撑，对我国“山地式”页岩气在复杂地腹构造条件下高效绿色勘探、开发具有重要指导意义。



The Wufeng-Longmaxi formations in the southern Sichuan Basin are the focus of marine shale gas in China. However, the shale gas in this area is still faced with technical bottlenecks such as unclear exploration understanding of “sweet spot” and complex events in drilling engineering. Those formations are the important regional detachment layers, showing a strong disharmony between intra-layer structure and regional structure. Previously, the layers are often used as regional weak layers for macro-study but lacked in the intra-structures. When complex structural systems such as folds, faults, and fracture zones are in the shale gas production layer, the difficulty of exploration and development will be greatly increased. Therefore, clarifying the style, type, and distribution of complex structures in the shale layers and their relationship with regional structures will promote the efficient, safe, and sustainable development of shale gas.

By field survey, the study of tectonic evolution and tectonophysics simulation experiments, to provide geological theoretical constraints for the precise seismic analysis of intra-layer structures: (1) to analyze the fold-fault genetic mechanism of the overlying and underlying strata, and clarify the genetic relationship between intra-layer structures and regional structures; (2) to analyze the genesis and evolution of tectonic-sedimentation in southern Sichuan, and clarify the formation process and dynamic mechanism; (3) to build simulation models, determine boundary conditions, carry out tectonophysics simulation experiments, and clarify the transformation between displacement and deformation between strong-weak interlayers.

Based on the above constraints, the dip, azimuth, curvature, chaos, variance, mean square error amplitude, reflection intensity, generalized spectral decomposition, ant tracking, and other attributes are extracted from the 3D seismic data in the Luzhou area, southern Sichuan. The potential complex structures in shale layers are described finely by using fault-related folds, interlayer shear slip, plane strike-slip theories, and so on. Clarify the structural configuration relationship of folds, faults, and fractures. Furthermore, two types of favorable intra-shale structures are determined: intra-layer shear structures and distal structures of intra-layer fault-related folds; and three types of unfavorable shale structures: proximal end of intra-layer fault-related folds, intra-layer strike-slip associated structures, and fold core extensional structures, and explain the development and patterns of fractures under different types of intralayer structures. The analysis results have been used to verify and predict several drilling platforms, and gratifying results have been achieved.

This study defines and characterizes the intra-layer structures of shale in southern Sichuan, primely. The results provide scientific support for shale gas “sweet spot” prediction, drilling layout, drilling guidance, and engineering risk prevention. It has important guiding significance for the efficient and environment-friendly exploration and development of "mountain" shale gas in China under complex hinterland structural conditions.