构造变形对页岩纳米孔隙结构及吸附/解吸性能的制约

Nanopores are well developed in shale reservoirs，which provide primary reservoir space for shale absorbed gas accumulation. The absorbed shale gas content is a key parameter for shale gas resources evaluation and exploration & exploitation. The Paleozoic strata in Southern China experienced complex tectonic movement, leading to shale strata deformation, which has significant effect on pore structure evolution. Furthermore, the tectonic deformation controls the process of shale gas adsorption/desorption. However, the characteristics of shale deformation and the mechanisms of the deformation effects on nanopore structure evolution are not well discussed, which hindered the shale gas occurrence mechanism. Marine shale samples with different structure evolution properties from the Paleozoic strata in Southern China are collected and multi-scale observation and experiment methods are combined to further study the macro to micro scale deformation characteristics and rules of shale, to understand the characteristics and evolution mechanisms of the shale pore structure under different deformation process，to establish nanopore structure models before and after deformation, to discuss the rules of adsorption/desorption in shale under different deformation process and finally，to clarify the effect of deformation on nanopore structure evolution and adsorption/desorption properties in marine shales. The results can be of great significance in further understanding the deformation mechanisms of shale, the nanopore structure characterization and shale gas occurrence mechanisms. Furthermore, this project has significant guidance for marine shale gas exploration and exploitation in complexly deformed area of Southern China.

页岩储层纳米孔隙极其发育，是页岩吸附气的重要赋存空间，而页岩吸附气含量是页岩气资源评价和勘探开发的关键参数。我国南方古生界经历多期复杂构造运动，构造变形普遍发育，对页岩孔隙结构及其演化具有重要影响，控制页岩气吸附/解吸过程。但是页岩构造变形特征及其对纳米孔隙结构的影响机制尚不明确，制约了页岩气赋存机理研究的深入。本项目以我国南方古生界不同演化特征页岩为研究对象，采用多尺度结合的研究方法，开展自然变形和实验模拟变形页岩的对比分析，精细研究页岩宏-微观变形行为和特征；阐明不同变形作用下页岩纳米孔隙结构特征及演化机制，建立变形前后纳米孔隙结构模型；揭示不同变形机制页岩吸附/解吸规律，剖析构造变形对页岩纳米孔隙结构及吸附/解吸性能的控制机理。预期成果将厘定页岩构造变形机制的判识、深化页岩纳米孔隙结构及页岩气赋存机理研究，具有重要理论价值，对我国南方复杂变形区页岩气的勘探开发也具有重要指导意义。

本项目以我国四川盆地古生界不同演化特征页岩为研究对象，以构造作用为切入点，重点研究了构造作用对页岩微纳米孔隙结构和吸附/解吸性能的影响：从页岩宏微观纳米孔隙结构入手，分析了页岩微纳米孔隙结构对变形作用的响应；揭示了不同变形机制、不同构造部位页岩储层物性的变化特征及规律；探索了变形页岩超微结构形成的原因以及对页岩储层物性的影响。 研究表明：（1）页岩微纳米孔隙的变形演化过程主要包括有机孔隙形状的改变，闭合消失，刚性颗粒挤压破碎，黏土层褶皱或形成高角度断裂，溶蚀封闭孔隙延展等。所有类型孔隙变形过程中都会出现互相连通的现象，形成从几纳米到几十微米不等的微裂隙，导致页岩连通性增强，为识别页岩微观和纳米级孔隙变形特征提供了依据。（2）变形页岩总孔体积和总孔比表面积增加，中小孔逐渐减少，大孔增加，韧性变形页岩大孔增加幅度远小于脆性变形影响的页岩。变形作用导致储层储集性和渗透性均增强。强变形（韧性剪切带、褶皱核部，断层部位）页岩的孔隙度和渗透率远高于弱变形（褶皱翼部，远离断层部位）页岩和未变形页岩。韧性变形页岩的储集空间高于脆性页岩，有利于页岩气的吸附。脆性变形渗透性高于韧性变形页岩，更有利于页岩气渗流和运移。（3）首次在断层（剪切作用下）内部观察到有机质层片结构，同时也观察到了无机纳米球粒。两种结构都为断层部位的小孔隙和储集空间的增加具有重要影响。认为断层部位的页岩有机质经历了从生成初期的无定型状态-芳香层片定向-拉伸延展，导致孔径增大连通性增强的过程。无机纳米球粒以颗粒流的方式重排定向，保存和提高孔隙数量，增加储集空间。 中国海相页岩大部分经历了复杂的构造作用过程，从变形的角度入手，分析变形页岩储层物性变化，探索脆性变形中超微结构现象形成的原因和可能对页岩气储集运移的影响等问题，可能是一条新的研究思路和途径，可以为页岩气构造因素评价，预测有利区块等提供数据支持和理论依据。