古生界页岩含气性原生有机质控制作用研究

Despite significant shale gas exploration in China, commercial shale gas has only been developed in the Silurian Fuling shale play. The limited commercial success suggests that shale gas deposits are very complicated in China. Therefore, it is very important to deepen our understanding of the main factors for shale gas enrichment and characteristics of shale gas distribution. This project will focus on key scientific questions in the context of “Control significance of primary organism on gas bearing in Paleozoic shale” . The research will follow four approaches. Firstly, the compositions of bio-precursor organisms and their (especially graptolite organisms) hydrocarbon generation potential will be quantitatively analyzed through a combination of ultramicro-morphology organic petrology methods, and hydrocarbon generation simulation technologies and hydrocarbon generation kinetics studies. The objectives are to determine the bio-precursor composition of the shales from Wufeng–Longmaxi formations of late Ordovician to early Silurian (O3w-S1l) and early Cambrian (∈1q), and their (especially graptolite organisms) hydrocarbon generation mechanisms. Secondly, hydrocarbon generation differences of shale generation potential and gas store ability of different organisms will be determined through combination with in-situ and high precision image analysis technologies and hydrocarbon generation simulation technologies. Thirdly, hydrocarbon generation simulation experiments on low maturity samples will be coupled with 2D and 3D microstructure analysis and pore size characterization. The distribution and evolution of porosity within organisms will be carefully analyzed by technologies such as adsorption-mercury methods, with the goal to build a full scale model of pores associated with different bio-precursor organisms. The analytical results will be used to determine the mechanisms and control factors for porosity development and evolution as a function of maturity, and establish hydrocarbon pore formation and evolution models of different bio-precursor organisms. Fourthly, through high temperature and high pressure adsorption isotherm experiments combined with gas isotope studies, the occurrence of free gas space and the retention mechanisms will be investigated and the main pore space for shale gas will be determined, and mechanisms for free gas retention and enrichment will be revealed combined with the results from the macro-geological reserved condition and pressure closed and diffusion mechanism of microscopic capillary. Investigation of these scientific issues will promote foundation theoretical researches for mechanisms of shale gas reservoir formation and evolution, and regularities of shale gas enrichment and distribution, and will provide theoretical guidance and reference for shale gas exploration specific to China, especially for marine shale gas exploration in southern China.

我国古生界页岩气勘探仅在焦石坝志留系页岩中实现了商业突破，勘探揭示页岩气聚集的复杂性，亟待从机理上深化认识页岩含气性主控因素及分布规律。本项目以“古生界页岩含气性原生有机质控制作用研究“为核心问题，以焦石坝、永川和威远探区（O3w-S1l）和井研-犍为探区金石1井（∈1q）页岩为解剖对象，利用超显微组分分析、成烃成孔模拟实验等，查明页岩中原生有机质成烃生物来源及生烃潜力分布特征，探索志留系页岩中笔石成烃潜能；结合微观结构精细分析等，解析多尺度有机孔形成主控因素，阐明不同有机质对页岩气形成和储集的贡献差异；加之等温吸附实验、有机质赋存状态及气体地球化学研究，查明游离气主要储集空间，结合宏观保存条件、毛细管压力封闭及扩散机制分析，揭示游离气滞留富集机制；综合分析成烃生物组合与含气性关系、页岩含气性主控因素及分布规律。本项目研究能够促进我国页岩气藏的形成演化机制与富集分布规律基础理论研究，对我国页岩气，尤其南方海相页岩气的勘探研究具有重要意义。

随着页岩气勘探的深入，发现页岩气富集规律极为复杂，归因于古生界复杂的地质演化过程。TOC的原生有机质构成和笔石的成烃潜能、有机孔形成演化机理、游离气赋存空间及滞留富集机制是页岩气富集规律研究中备受关注的关键科学问题。对此，本项目开展了成烃生物组合及笔石生烃能力、有机孔形成与演化机理研究、游离气赋存空间与滞留机制等三方面研究工作。通过有机岩石学、微观结构、等温吸附、物理与数值模拟实验等多手段跨学科综合研究，一是解决了龙马溪组主要有机质成分－笔石对页岩气生成和储集贡献这一悬而未决的难题：认识到笔石是TOC的贡献者之一，具II2型干酪根的生烃能力；通过其自身原生孔缝及大量聚集分布与其它有机质、矿物相互组合构成复杂的孔缝系统，成为页岩气重要的储集空间、连通和运移通道。二是揭示了有机孔发育的主控因素和非均性的成因，建立了海相富有机质页岩有机孔形成演化模式，为我国页岩气储层精细评价提供了关键参数和理论依据：提出有机孔发育的强非均质性归因于不同类型有机质的组分、结构及生孔机制的差异性，有机孔形成与保持受控于烃源岩的沉积环境、生烃全过程和成岩作用三元因素的联合控制机制。三是查明了页岩气不同埋藏条件下赋存形式、储集空间及滞留机制，为不同地质条件下页岩气赋存机理和分布预测提供了新的技术途径和理论依据：建立了页岩气赋存形式的TOC-孔体积-埋藏条件三元定量模型，页岩气主要以单层吸附形式吸附于微孔，超压下以游离气为主，游离气主要赋存于介孔及以上孔缝；页岩气封存起始期与生烃高峰期匹配且后期构造改造强度弱是页岩气富集的关键，提出“超临界态-吸附作用-毛管压力-低速扩散”综合作用、动态演化的页岩气滞留机制。参加国际性和全国性学术会议并做口头报告8人次。第一标注发表论文22篇（SCI 7篇，EI 4篇）。申报发明专利5项。牵头制定能源行业标准1项。培养研究生7人（博士5人，硕士2人），出站博士后2人。