页岩孔隙演化及其与残留烃量的关系:来自地质过程约束下模拟实验的证据

Relationship of Porous Evolution and Residual Hydrocarbon: Evidence from Modeling Experiment with Geological Constrains

加强页岩孔隙演化规律研究,特别是定量评价其与残留烃之间的关系对页岩油的勘探具有重要意义。采集鄂尔多斯盆地低成熟度湖相Ⅰ型富有机质页岩,通过地质条件约束(埋藏史、地层压力、地层水矿化度等)成岩物理模拟实验模拟页岩演化,利用压汞法、氮气吸附法和二氧化碳吸附法获得不同温压段页岩的比孔容、比表面积和孔径分布,结合氯仿沥青A抽提定量结果,确定孔隙演化规律及其与残留烃的关系。结果表明页岩大孔比孔容与残留烃含量先增加后减小,微孔和中孔的比孔容随着模拟实验温度的增加呈现先减小后增大。XRD分析显示黄铁矿含量控制大孔,有机质丰度和粘土含量控制微孔和中孔。微孔和中孔的比孔容增加为高—过成熟度阶段页岩气提供储集空间,大孔比孔容与残留烃含量变化一致,生油窗阶段大孔增加是页岩油的有利储集带。

Enhancing study of porous evolution of shale is of great significance for petroleum exploration in shale, especially for assessing the relationship of porous evolution and residual hydrocarbon quantitatively. Preventive lacustrine source rocks of type I with low maturity in Ordos Basin were collected and selected for modeling experiment of physical diagenesis in shale, combing with geological constrains of burial history, formation pressure and formation water salinity. Utilizing methods of mercury intrusion, nitrogen adsorption, CO2 adsorption we acquire specific pore volume, specific surface area and pore size distribution of shale in different temperature and pressure. In combination of ultrasonic extraction of bitumen ＂A＂ in trichloromethane, we try to figure out the relationship of porous evolution and residual hydrocarbon. Ultimately, we seek to interpret porous alteration by integrating analysis of TOC, XRD in whole rock and XRD in clay minerals. Results show that specific pore volume of macropores increase and then decrease with residual hydrocarbon, while in micropores and mesopores, specific pore volume decrease first and then increase with the rises of modeling temperature. XRD analysis presents that mineral contents are the controlling factor of macropores, and TOC and contents of clay minerals control micropores and mesopores. Enlargement of specific pore volume in micropores and mesopores implies remarkable reservoir space for shale gas generated in high-over maturity stage of kerogen pyrolysis and oil cracking. Specific pore volume of macropores varies consistently with residual hydrocarbon. Increase of macropores in oil window response to the favorable entrapment zones of shale oil.