中扬子下古生界高演化海相页岩有机质孔隙微观结构差异性及富集规律

The organic matter[OM]-hosted pores are regarded as the most critical storage capacity within high thermal evolution shale. Study on the OM-hosted pore system is not only associated with the accumulating mechanism of high thermal evolution shale gas, but also has the fundamental theoretical significances to accurately evaluate the characterizaton of shale reservoir property and shale gas potential, to predict the best target of shale gas and optimize technologies of shale gas development. We are focusing on the high thermal evolution marine organic-rich shales, which is composed of the underlying Upper Ordovician Wufeng formation and the Lower Silurian Longmaxi formation. This project will classify the shale into several types considering "multi-factors", including lithofacies and lithology, characteristics of organic matter, inorganic mineral components and pore size distribution. In micron space and nano-scale level, some advanced electron microscope analyzing techniques and testing techniques will be applied to carry the comparative study on the pore structure characteristics, distribution and connectivity of OM-hosted pores through characterizing the occurrence and shape of organic matters and the pores within them. The objectives of this project are to illuminate the microstructure differences of the OM-hosted pore in marine shale of high thermal evolution, analyze the controls of the dispersive organic matter and inorganic mineral on the formation and distribution of OM-hosted pores and their intrinsic relationships, and investigate the occurrence and distribution characterization of OM-hosted pores within high thermal evolution shale. The results will be significant to enhance the understanding on the OM-hosted pores of high thermal evolution shale, and provide the theoretical basis and scientific guidance to the reservoir research, exploration and development, and resource evaluation of high thermal evolution shale.

有机质孔隙是高演化页岩最主要的储集空间类型，针对有机孔隙的系统研究不仅关系到高演化页岩气富集机理问题，而且对正确评价高演化页岩储集性和页岩气储层规模，预测有利富集区，优化开发工程技术都具有基础理论意义。本选题以中扬子西部上奥陶统五峰组-下志留统龙马溪组高演化海相富有机质页岩为主要研究对象，在开展岩相岩性、有机质特征、无机矿物成分和孔径分布等"多因素"页岩分类的基础上，通过实验室显微观测和成像技术，在微米空间、纳米尺度下，对页岩有机质的不同赋存特征及其发育的有机孔隙的结构特征、分布规律和连通性进行精细刻画和对比研究，揭示高演化页岩有机孔隙结构上的差异性，深入分析有机质载体及其依附矿物成分对有机孔隙形成和分布的控制作用，探讨高演化页岩有机质孔隙的富集分布规律。所得结论将有助于深化对高演化页岩有机孔隙的认识，为高演化页岩的储层研究、勘探开发和资源评价提供理论依据和科学指导。

富有机质页岩既是气源岩又是天然气储集层，天然气可以游离态储存在页岩天然裂缝和粒间孔隙中，也可吸附于干酪根和黏土颗粒表面，或者溶解于干酪根和沥青中。北美页岩气商业产层的页岩平均孔隙度主要分布在4.22-6.51%之间，渗透率普遍低于1mD。这种低孔低渗的储层特征主要归因于富有机质页岩内部纳米至微米级别的孔隙系统。深入开展富有机质页岩孔隙类型、孔隙结构特征研究，分析影响孔隙富集的主要因素，评价页岩储层孔隙的气体储存性能，不仅对页岩气含气性评价、页岩储层开发意义重大，而且对潜在含气页岩勘探策略的设计和实施至关重要。.本项目以中扬子下古生界海相页岩（寒武系水井沱组、奥陶系五峰组-志留系龙马溪组）为主要研究对象，辅以中生界陆相页岩（侏罗系自流井组和额木尔河组）的对比研究，通过扫描电镜观察、二氧化碳和氮气吸附、高压压汞等实验方法，划分了页岩孔隙类型，刻画了页岩孔隙结构特征，并结合页岩有机地球化学和矿物成分分析、高压甲烷等温吸附实验，总结了页岩孔隙富集的影响因素，探讨了页岩孔隙结构对甲烷吸附能力的影响。.主要成果认识包括：1）扫描电镜观察发现，高演化五峰组-龙马溪组海相页岩主要发育有机质孔隙，处于极高成熟阶段的水井沱组页岩孔隙欠发育，而相对较低成熟度的侏罗系页岩主要以无机孔隙为主，仅发育少量有机质孔隙；2）孔径分析表明，从水井沱组、五峰组-龙马溪组海相页岩到侏罗系陆相页岩，孔径分布的主要范围由以微孔-中孔为主向以中孔-宏孔为主过渡；3）有机质丰度是高演化页岩孔隙发育的重要影响因素，有机碳含量越高，有机质孔隙越发育；4）随着热演化程度升高，页岩的孔隙网络系统具有由以无机孔隙为主转变为以有机质孔隙为主的趋势；5）有机质孔隙是影响高演化富有机质页岩吸附能力的最主要因素。