页岩流变的纳米效应及其赋气机理研究

Shale in superficial lithosphere is a soft rock distributed comprehensively in the earth surface，and tends to detachment along beddings forming deformation or rheology at various types and strength due to interlaminar shearing action, which is quite different from felsic rock and coal. Shale in most basins in China is supposed to generate rheology, even if suffering from weak interlaminar shearing. Shale after rheology possesses strong nano effects, producing both nano particles and nano pores. Nano pores of shale are the important space storing shale gas. In this research, new multidisciplinary theories are considered, and modern advanced experimental and testing techniques are applied. Based on the observation of shale rheology at macro and micro scales under natural condition, the deformational experiments will be carried out at different temperatures and pressures, and the rheological characteristics under natural and laboratorical conditions are compared carefully, which aids in illustrating the rheological behavior and mechanics due to shearing along bedding. Meanwhile, the nano effects of minerals, organic matter and pore structures in rheological shale at different deformational mechanisms will be analyzed intensively, to discuss the evolving process of nano pore structures. Furthermore, the model of nano structure of shale after rheology will be established according to the rheological features and its nano effects. Finally, the gas accumulative mechanism and related restrictive factors of shale after rheology will be revealed. This research will not only enrich and expand the understanding of rock rheology and the multiphase medium flow on crust, but also provide scientific basis for resolving the important geological problems of shale gas exploration and development in various tectonically deformed area.

位于地壳浅层次沉积岩层中的页岩是广泛分布的软弱岩石，在层间剪切作用下易发生顺层滑动而形成不同类型和不同强度的变形或流变，且与长英质岩石或煤岩差异较大。我国大多数盆地中的页岩即使仅经历较弱的层间剪切，也会产生流变；页岩流变后具有显著的纳米效应：既产生纳米颗粒，又产生纳米孔隙；而页岩的纳米孔隙结构是页岩气的重要赋存空间。本项研究基于多学科交叉的研究思路，结合先进的实验和测试方法，以天然条件下页岩流变宏微观观测为基础，并与不同温压变形实验的流变特征进行对比，以阐明页岩在顺层剪切作用下所形成的流变行为与机制；深入研究页岩流变的矿物与有机质结构及其孔隙结构的纳米效应，探讨页岩流变的纳米孔隙结构演化过程；在此基础上，建立流变后页岩的纳米结构模型，进而揭示其赋气机理与制约因素。这些研究可丰富和发展对地壳中岩石流变和多相介质流动的理论与认识，并为解决不同构造变形区页岩气勘探开发重要地质问题提供科学依据。

本次研究以四川盆地、鄂尔多斯盆地和闽西南地区为研究对象，以天然条件下页岩流变宏微观观测为基础，并与不同温压变形实验的流变特征进行对比，阐明了页岩在顺层剪切作用下所形成的流变行为与机制。深入研究了页岩流变的矿物与有机质结构及其孔隙结构的纳米效应；建立了流变后页岩的纳米结构模型，揭示了流变页岩的赋气机理与制约因素。获得主要成果和认识如下：.（1）页岩层受到构造应力作用容易发生流变，主要流变类型有韧性流变、脆性流变和脆韧性流变。页岩流变在宏观上产生了不同的流变构造，包括裂隙、褶皱、页岩揉皱等；微观上发现页岩结构从脆性流变：微裂隙、碎裂流动至韧性流变：显微褶皱以及S-C组构转变，黄铁矿晶体以及有机质孔隙呈定向排列。通过气体吸附实验等研究表明，页岩韧性流变增加了微-纳米孔隙所占的比例以及孔隙比表面积。.（2）不同温压条件下的页岩变形实验表明：在温度T<90℃、围压P<60MPa时为脆性变形阶段，主要以破裂变形为主；脆韧性过渡阶段（90℃<T<200℃，60MPa<P<110MPa）的页岩，以部分膨胀变形或产生粘滑现象为主；韧性变形阶段（T>200℃，P>110MPa）的页岩出现整体的体积膨胀，产生了显著的流变现象。.（3）页岩力学特性主要包括强度与变形两个方面。通过页岩直接剪切试验，建立了抗剪强度表达式；在剪切力作用下，页岩沿先存剪切裂隙的方向破裂，同时产生次一级裂隙并形成裂隙网络；通过剪切流变试验，提出了页岩流变的粘-弹-粘弹性元件模型。.（4）流变后的页岩具有如下特征：① 页岩层间产生多组裂隙；② 微-纳米孔隙显著增多；③ 连通性增强；④ 赋气状态由游离气转化为吸附气。另一方面，与弱变形相比，较强变形程度的页岩样品微纳米孔隙发育，构造变形作用显著增加了页岩的赋气性。.这些研究可丰富和发展对地壳中岩石流变和多相介质流动的理论与认识，并为解决不同构造变形区页岩气勘探开发重要地质问题提供科学依据。