海相油页岩的生烃动力学特征——以燕山地区下马岭组油页岩为例

油页岩是未来重要的补充与替代能源。通过开放体系程序升温热模拟实验,对燕山地区下马岭组海相油页岩进行了研究。结果表明:其热裂解反应主要发生在440～480℃,表观生烃活化能集中分布于170～290 kJ/mol,主峰约为240 kJ/mol,明显高于陆相油页岩(抚顺油页岩和茂名油页岩),而与下古生界海相烃源岩(甘肃平凉奥陶系灰岩及爱沙尼亚奥陶系Kukersite油页岩)活化能分布范围及主峰位置相似。以ICP技术规范为例,在相同热历史条件下,通过数值模拟认识到下马岭组海相油页岩主生烃温度为275～325℃,高于湖相油页岩(265～305℃),而与下古生界海相烃源岩相似,表明其可能具有与古生界海相有机质相似的生烃机理。     

A New SHRIMP Age of the Xiamaling Formation in the North China Plate and Its Geological Significance

Setting up the hypostratotype of late Precambrian is the main aim of the research on the Meso- and Neoproterozoic in North China. The chronostratigraphic position is the key in this study. However, many key horizons have not been calibrated with the high-quality isotopic ages. Using the reported new U-Pb age with the Sensitive High-Resolution Ion Microprobe (SHRIMP II), a zircon U-Pb age was obtained of the ash bed in the Xiamaling Formation in North China Plate, yielding a weighted mean 206Pb/238U age of 1368±12 Ma. It is the first SHRIMP U-Pb age from the Xiamaling Formation in the North China Plate, and represents the depositing time of the middle part of the Xiamaling Formation. The zircon age plays an important role to understanding geological evolution of the North China Plate during Meso- and Neoproterozoic.     

张家口下花园青白口系下马岭组灰质页岩热模拟实验

华北地区中上元古界地层烃源岩的有机质热演化普遍处于高成熟－过成熟阶段，而张家口下花园青白口系下马岭组页岩和灰质页岩的Rb仅有0.38-0.6%，处于低成熟阶段，是系统研究中上元古界地层的生烃模式及有机质热演化特征的较理想模拟实验样品。本次模拟结果表明：模拟温度在275℃以前（R0＜0.80%)为低成熟阶段，275℃－350℃（R0为0.8-1.32%）为成熟阶段；其中325℃（R0为1.16%)为生油高峰，350℃（R0为1．32％）为轻质油高峰，350℃－410℃（R0为1．32－2．0％）为高成熟阶段，410℃以后（R0＞2．0％）为过成熟阶段。随着温度升高，生成的烃类和干酪根碳同位素（δ^13)逐渐变重，验证了δ^13C存在温阶效用。在过成熟阶段，可溶有机质亦发生了芳核的缩聚反应，使芳烃含量减少，大分子的沥青质含量增多。可溶有机质在高成熟－过成熟阶段有“逆转”现象，正构烷烃碳数分布出现了双主峰，高碳数部位出现了奇偶优势等特征。当Rb>0.81％以后，同一温度点为Rb%>R0%。无水与加水模拟实验对比表明，加水实验的液态烃产率高，液态烃中重组分相对含量多，说明无水实验中热裂解反应强烈，而加水实验更接近地层热演化条件。