干酪根结构及可溶有机质析出对有机孔隙演化的影响

Organic porosity in organic-rich shale is important for storage of shale gas and tight oil in shale reservoirs. The complicated coupling relationship between Kerogen structure, Soluble bitumen and organic porosity evolution are still plaguing for shale oil and gas resources evaluation. As organic-rich shale thermally matures and enters the oil window, generated bitumen and oil can fill pore spaces, block pore connectivity, and reduce porosity. Organic pore evolution mechanism is a key basic research for shale gas and tight oil exploration..Source rocks with low maturity will be collected and selected for modeling experiment of physical diagenesis in shale, combing with geological constrains of burial history, formation pressure and formation water salinity. And the Artificial evolution series samples of organic-rich shale can be obtained from the modeling experiment. And then, The pore structure parameters of samples can be obtained by the high resolution scanning electron microscopy (SEM) and Low-pressure N2 and CO2 adsorption techniques, which usually were used to quantify mesoporosity (pore size 2～50 nm, accessible to N2 and CO2) and microporosity (pore size <2 nm, accessible to CO2 only), after fractional Ultrasonic extracted in different solvent. The small molecular phase structure characteristics of Soluble bitumen were analyzed by GCMS,FTIR. and Kerogen structure will be obtained by NMR, FTIR technology. Influence of kerogen structure and hydrocarbon expulsion on organic pore evolution will be discussed. Research results will not only be helpful for understanding on organic pore evolution mechanism and the hydrocarbon generation and expulsion mechanism, but also provide inspiration and guidance for resource evaluation and exploration and development plan of shale oil and gas.

有机孔隙演化机理是页岩油气勘探和石油地质学及有机地球化学领域的前沿研究课题，也是亟待深入研究的薄弱环节。针对烃源岩内滞留沥青与干酪根结构和有机孔隙演化之间的耦合关系，采用地质条件约束的成岩物理模拟获得富有机质页岩的人工演化系列样品，并采用不同溶剂各样品分级抽提，逐级溶出小分子相，改变干酪根的孔隙结构，然后借助高分辨率扫描电镜和低温N2和低温CO2吸附法，获取抽提残余物的孔隙结构参数，再结合GCMS、NMR、FTIR等技术，研究不同溶剂抽提出小分子相的结构特征和干酪根结构变化规律，探讨不同溶剂抽提后有机孔隙演化的规律，深入分析干酪根结构和可溶沥青对有机孔隙演化的影响，必将对深化干酪根生、排烃规律与机理及有机孔隙演化机理的认识，也将为页岩油气资源评价和开发方案制定提供启示和指导。

页岩有机孔隙演化规律是页岩油气勘探甜点预测过程中必须要解决的基础问题之一。本项目通过自然演化样品与人工演化样品的实验分析，综合对比分析了热演化过程中干酪根、可溶有机质与页岩有机孔隙协同变化特征。在生烃过程中，干酪根结构出现两次突变，将有机质演化分为三个阶段，分别是去官能团阶段、脱甲基与芳构化阶段和趋石墨化发展阶段。在不同阶段可溶有机质与干酪根进行耦合，一部分发生二次裂解转化为更轻的烃类，一部分缩合至干酪根结构中对有机孔隙发育产生影响。综合分析认为，热成熟度是有机孔隙发育演化的主要控制因素，在整个热成熟的不同阶段具有不同的演化特征。在中低成熟阶段（0.72％~0.83％Ro），有机质纳米孔很少且发育缓慢，>10nm被可溶有机质充填；在生油高峰期（0.83％~1.05％Ro），强烈的生排烃作用导致的有机质纳米孔的形成，部分微孔中充填可溶有机质;生油窗晚期（1.05％~1.25％Ro），大孔和中孔中残留油的裂解成轻油和湿气并排烃，有机孔结构参数略有增加；Ro 1.25％~1.5％，固体沥青由于残留油的裂化导致一部分孔堵塞，导致孔结构参数降低，并且由于其进一步开裂，在不同尺寸孔中出现的残留油明显减少。