惠民凹陷上古生界煤系烃源岩生烃潜力

Hydrocarbon generation potential of Upper Paleozoic coal-derived source rocks in Huimin sag

针对渤海湾盆地东部惠民凹陷上古生界石炭—二叠系的煤系烃源岩的生烃潜力评价问题,为了从多方面综合研究以揭示区内发现具有工业价值的煤成气藏并显示出良好的煤成气勘探潜力的原因,通过对煤系烃源岩有机地球化学特征的研究,结合黄金管封闭体系高温高压生烃热模拟及烃源岩热演化史数值模拟,对区内煤系烃源岩生烃潜力及生烃过程进行了分析。结果表明:研究区内上古生界煤系烃源岩层系中不同岩性的有机质丰度差异较大,其中煤岩显示出中等-较好的烃源岩等级;有机质类型以高等植物来源为主的Ⅱ_(2)-Ⅲ型有机质类型为主;有机质热演化程度受控于区域内构造特征的变化,从低熟-过熟阶段均有分布。此外,封闭体系生烃动力学特征表明,区内煤系烃源岩烃类产率较高,单位总有机碳(total organic carbon,TOC)中的最大液态烃产率和气态烃产率分别超过90 mg/g和180 mL/g。结合烃源岩热演化史模拟结果得出,研究区内煤系烃源岩晚期二次生烃潜力较大,二次生烃产率约占总生烃产率的40%~50%,显示出良好的晚期二次生烃潜力。

To achieve effect evaluation of the hydrocarbon generation potential of the Upper Paleozoic Carboniferous-Permian coal-measure source rocks in Huimin sag,eastern Bohai Bay Basin,a comprehensive study from various aspects is necessary to reveal the reasons for the discovery of coal-derived gas reservoirs with industrial value and good exploration potential.The hydrocarbon generation potential and process of coal measure source rocks were analyzed on the basis of an overall condideration of the study on organic geochemical characteristics of coal measure source rocks and the thermal simulation of hydrocarbon generation at high temperature and high pressure in gold pipe closed system and the numerical simulation of thermal evolution history of source rocks.The results show that the abundance of organic matter in different lithologies of Paleozoic coal measure source rocks varies greatly in the study area,and the coal rocks show medium to good grade of source rocks.TypeⅡ_(2)-Ⅲorganic matter mainly comes from higher plants.The degree of thermal evolution of organic matter is controlled by the changes of tectonic characteristics in the region,and it is distributed from low maturity stage to over maturity stage.In addition,the hydrocarbon generation kinetics characteristics of the closed system indicate that the coal measure source rocks in the study area have a high hydrocarbon yield,with the maximum liquid and gaseous hydrocarbon yields exceeding 90 mg/g and 180 mL/g of per unit of total organic carbon(TOC),respectively.Combined with the simulation results of the thermal evolution history of source rocks,it is concluded that the coal measure source rocks in the study area have a high potential for secondary hydrocarbon generation in the late stage.The secondary hydrocarbon generation rate accounts for 40%-50%of the total generation rate,indicating a good potential of late secondary hydrocarbon generation.