中国南方寒武系页岩有机质、流体和孔隙演化耦合机制研究

The shale gas content of Cambrian Shale, southern China can neither be predicted by thermal maturity model that is workable to US shale plays, nor by the Wufeng–Longmaxi Formation shale model that TOC content and post-tectonic preservation are key factors to shale gas sweet-spot prediction. The mechanism of organic matter hosted pore evolution in Cambrian marine shale is unique and remains unclear, likely leading to significantly regional variation in shale gas content of the Cambrian marine shale. In a view of geological history evolution, the proposed study on pore formation and evolution in the Cambrian shale is coupling with the histories of organic matter conversion, oil and gas formation and organic-matter hosted pores evolution. High-resolution geological and geochemical core wells or outcrop sections will be studied to reconstruct organic matter accumulation model of the Cambrian shale; to investigate the mechanism of inorganic and organic pores formation in the highly-matured shale; and to evaluate the controlling factors to the Cambrian shale gas sweet spot. Fluid inclusions of calcite cements and quartz cements filled in the natural factures of Cambrian shale will be analyzed to restore the history of oil and gas generation, expulsion, retention and preservation in the Cambrian marine shale in southern China. Gold-tube pyrolysis of miniature core plugs under high temperature and high pressure conditions, combined with detailed oil and gas geochemical characterization, SEM pore imaging analysis, N2 isothermal adsorption, and CH4 isothermal adsorption experiments, will be conducted for the development of kinetics model of organic-matter hosted pore formation and evolution. On the basis of integrated studies on the field observation and laboratory’s results (including fluid inclusion and gold-tube pyrolysis), the conceptual model of coupling mechanism among organic matter evolution, shale gas formation, and pore evolution in Lower Paleozoic Cambrian marine shale in south China will be established and serve for the Cambrian Shale gas content prediction.

中国南方寒武系海相页岩含气性在不同地区差异较大，有机质孔隙发育机制不清楚，无法直接用控制五峰组—龙马溪组页岩含气性的有机质丰度和后期构造活动对页岩气保存来预测。本研究提出采用历史演化的观点，在动态的条件下研究孔隙形成和发育机制，恢复南方寒武系页岩有机质转化、油气形成和有机孔演化的历史。通过高精度精细地质地球化学自然剖面研究，建立寒武系海相页岩有机质富集模式，分析高演化条件下孔隙发育机制，评价寒武系页岩气的主控因素。通过页岩中裂缝或裂纹充填的碳酸盐/硅质胶结物流体包裹体研究，恢复寒武系页岩油气形成、排烃、滞留和保存历史。通过岩石小柱体高温高压金管热解模拟实验，并结合SEM孔隙成像分析、氮气等温吸附以及甲烷等温吸附实验，建立有机孔形成、演化的动力学预测模型。在综合研究的基础上，结合自然剖面和实验室模拟结果，量化各种控制因素，建立寒武系页岩有机质演化、页岩气形成和孔隙演化耦合机制的概念模型。

中国南方寒武系海相页岩含气性在不同地区差异很大，孔隙发育机制不清楚，无法直接沿用五峰组―龙马溪组页岩含气性的预测方法，因而亟需完善和发展我国南方高-过成熟海相页岩气成藏理论。本重点项目以宜昌、威远和汉中3个寒武系页岩气获得突破区为重点研究区, 系统观测、采集了13个野外露头或钻井岩心剖面，完成了测试项目40余项，获得原始数据分析7556件次，建立了寒武系高精度精细地质地球化学典型剖面、有机质富集模式及有机质-孔隙-流体耦合概念模型，取得了以下几个方面的主要研究进展：1）提出了中上扬子地区寒武系富有机质页岩沉积的二分段性新认识，揭示陆源输入和化学风化控制了海水中氧化剂（硫酸盐、硝酸盐）变化对海洋碳、硫、氮循环的影响，明确了不同层段有机质来源和有机质保存的差异。2）开发了以岩石小柱体为研究对象的黄金管热模拟泥岩有机质-孔隙-流体耦合演化的实验手段，探讨了以II型干酪根为主的海相泥岩在不同成熟阶段油气形成、排出、滞留和孔隙演化的耦合关系。3）揭示了中上扬子地区下寒武统富有机质页岩孔隙发育的非均质性与岩相和矿物组成之间的内在联系，指出富有机质页岩上段是寒武系页岩气勘探的有利层段（甜点段）。4）厘定了中上扬子地区下寒武统页岩三个主要成烃阶段及相应温度条件，并结合方解石/白云石超低浓度U-Pb定年，揭示了喜山中晚期因构造抬升和裂缝化造成了活动构造区寒武系页岩气的大量散失，以及加里东中晚期-海西早期和海西晚期因构造抬升出现了两次生烃停滞。5）明确了寒武系页岩气中烃类气体和高含量氮气的成因，揭示了寒武系高氮页岩气的形成与页岩中含氮有机化合物和氨基粘土矿物发生高温热裂解脱氮作用有关，并探讨了热成熟度和后期构造保存条件对页岩气藏的影响。6）提出中上扬子地区寒武系优质烃源岩主要分布于绵阳―长宁裂陷槽、鄂西裂陷槽和湘黔渝深水陆棚―斜坡这三个古地理位置。在绵阳―长宁裂陷槽和鄂西裂陷槽环境下的寒武系构造保存条件较好，页岩含气量为理论总生成气量的10%~30%（最大甚至超过50%），是页岩气勘探的有利位置。上述研究成果有助于完善和发展我国南方高‒过成熟海相页岩气成藏理论，为寒武系页岩气勘探提供科学依据。现已发表标注论文52篇（第一标注论文48篇），其中SCI论文23篇，EI/核心论文29篇，培养博士后1名，博士、硕士研究生33名。