致密低渗页岩微观岩体结构特征及其对动态剪切特性的控制作用

Horizontal drilling is the basis for the shale gas exploitation, which involves the crushing process of the dense low-permeability shale induced by the drilling bit under dynamic shear. This process is usually influenced by the microscopic rock mass structure of the shale. However, there is a lack of quantitative characterization of micro/nano multi-scale rock mass structure of dense low-permeability shale, and few studies on dynamic shear properties of shale and its microscopic rock mass structure effect have been reported, which affects the development of horizontal drilling technology of shale gas. To overcome these problems, we write this proposal and intend to carry out researches on the characteristics of the microscopic rock mass structure for the dense low-permeability shale and its controlling effect on dynamic shear properties. Based on the geological background data and field investigation as well as sampling of the marine sediment shale in the north of Guizhou province, China, the micro/nano multi-scale structure images of the shale will be captured via micro/nano structure observing equipment. Then, the multi-scale rock mass structure of the dense low-permeability shale will be quantitatively characterized and typical microscopic rock mass structure models will be established. By making full use of the large-scale dynamic shearing setup of the rock mass, we will investigate the deformation and failure process as well as strength characteristics under dynamic shear for the shale with typical microscopic rock mass structures. On this basis, the discrete element numerical calculation software will be used to carry out the fine simulation of the dynamic shear test process for the shale with different microscopic rock mass structure, revealing the controlling effect of microscopic rock mass structure on the macroscopic mechanical parameters and the progressive failure process of dynamic shear for the shale, which will provide the theoretical support for the development of horizontal drilling technology of shale gas.

水平井钻井技术是页岩气开发的基础，涉及钻具对致密低渗页岩的动态剪切破碎过程，该过程受页岩微观岩体结构的制约。然而，当前缺乏对页岩微观-纳观多尺度岩体结构的定量刻画，鲜见页岩动态剪切特性及其微观岩体结构效应的研究成果，影响页岩气水平井技术的发展。本项目拟开展致密低渗页岩微观岩体结构特征及其对动态剪切特性的控制作用研究。基于我国黔北地区海相致密低渗页岩的地质背景资料和现场考察采样，首先利用微纳结构观测设备采集页岩微观-纳观多尺度结构图像，定量刻画其多尺度岩体结构特征，建立页岩典型微观岩体结构模型；然后借助大型岩体动态剪切性能测试试验系统研究具有典型微观岩体结构的页岩动态剪切变形破坏过程及强度特征的变化规律；在此基础上，通过离散元对具有不同微观岩体结构的页岩的动态剪切试验过程进行精细模拟，揭示微观岩体结构对页岩动态剪切宏观力学参数及渐进破坏过程的控制作用，为页岩气水平井技术的发展提供理论支撑。

页岩气水平井钻井涉及致密低渗页岩的动态剪切宏微观破碎过程，前人对致密低渗页岩微观岩体结构特征及其对动态剪切特性的控制作用研究十分欠缺，亟待深入。.针对上述问题，本项目历时3年，通过技术研发、理论研究、室内试验、数值模拟、野外科考等手段开展了较为深入系统的研究。研发了适用于致密低渗的各向异性储层页岩的动态剪切试验技术与装备，开发了系列软件；总结了页岩剪切破裂模式，提出了适用于页岩剪切破裂面的三维形貌定量刻画新方法，阐明了页岩剪切破裂面三维形貌的各向异性特征，揭示了储层页岩宏观动态剪切变形及强度特性的层理效应、尺寸效应和速率效应，建立了适用于储层页岩及其剪切破裂面的动态抗剪强度准则；构建了页岩典型微观岩体结构模型，揭示了各向异性储层页岩微观岩体结构特性；构建了各向异性储层页岩动态剪切渐进破坏过程的离散元模型，厘清了页岩动态剪切宏微观渐进破坏过程，揭示了微观岩体结构对页岩动态剪切宏观力学参数的控制作用。上述成果在工程地质和岩石力学等领域共发表国际SCI期刊论文12篇（NI论文1篇，Q1论文6篇）、授权国内外专利14项、登记软件著作权4项。.研发的适用于致密低渗的各向异性储层页岩的动态剪切试验技术与装备可为页岩动态剪切宏观力学特性的试验研究提供技术支撑。建立的典型页岩微观岩体结构模型及揭示的各向异性储层页岩动态剪切宏微观特性可为页岩水平井井周地层稳定性评价及页岩压裂裂缝的扩展演化预测提供理论支撑。定量刻画的各向异性储层页岩动态剪切宏微观渐进破坏过程对水平井钻头的优化设计、操作参数的优化以及辅助破岩工具的设计具有指导意义。因此，研究成果为页岩气水平井钻井技术及压裂技术的发展提供理论和技术基础，在岩体工程地质动力学领域和储层工程地质力学领域具有良好的应用前景。