沁水盆地石炭-二叠煤系地层烃源岩特征及生烃有利区评价

摘要

The hydrocarbon source rocks of the Carboniferous-Permian coal measures strata in Qinshui basin contain coal rock,mudstone and limestone.This paper analyzes and summarizes a large amount of the organic geochemical characteristic data about hydrocarbon source rocks.The result shows that the maceral composition of the coal rock samples of Lower Carboniferous Shanxi Group and Upper Permian Taiyuan Group in the Qinshui basin mainly contains vitrinite,followed by the inertinite,and the content of stable components (exinite + sapropel group)is low,generally <1.2%;H/C atomic ratio of kerogen is mainly 0.20 ~ 0.85,and O/C atomic ratio of kerogen is mainly 0.02 ~ 0.10, belonging to the high evolution stage Ⅲ type organic matter;the carbon isotope of the coal rock is common heavy,and the distribution range is - 23‰ ~ - 25.6‰;the content of the saturated hydrocarbon of bitumen “A”is commonly <25%,and that of the aromatics hydrocarbon is higher, the range is 11%~58%,the saturated hydrocarbon/aromatics hydrocarbon is generally <0.4.The maceral composition of the mudstone in the coal measures strata mainly contain vitrinite,followed by the inertinite,and the content of exinite is low;H/C atomic ratio of kerogen is 0.25~0.75,and O/C atomic ratio of kerogen is 0.03~0.20,belonging to the high evolution stage Ⅲ type organic matter, and a little belonging to the Ⅱ type organic matter;the carbon isotope of the coal rock is common heavy,and the distribution range is -23.5‰~-25.9‰;the content of the saturated hydrocarbon is<25%,commonly less than 20%.The Taiyuan Group limestone mainly contains Ⅱ2 type kerogen, and the carbon isotope is lighter than the coal rock and the mudstone of Shanxi Group and Taiyuan Group,ranging in - 26‰ ~ - 30‰. Finally, the paper evaluates the favorable hydrocarbon-generating areas of the hydrocarbon source rock strata of the coal measures strata in the Qinshui basin and draws the hydrocarbon-generating potential evaluation standard suitable for the coal rock and the mudstone of this area.The result shows that the coal rock of Shanxi Group in the Qinshui basin is medium-good hydrocarbon source rock in general.If only from the point of view of the organic matter abundance,the hydrocarbon source rocks in the two wings of the basin are good,that in the central and southern parts are medium-poor;the coal rock in Taiyuan Group is generally medium-good hydrocarbon source rock,the hydrocarbon source rocks in the two wings of the basin are mostly good, in the area of Qinxian-Qixian-Yuci-Yushe and the southern area,there are poor-medium hydrocarbon source rocks;the mudstone of Shanxi Group in the Qinshui basin is medium-poor hydrocarbon source rock,only that in part of the area in the west is good hydrocarbon source rock,the hydrocarbon potential in the middle area of the basin is poorer than that in the two wings;the mudstone in Taiyuan Group is middle-poor hydrocarbon source rock,the local area in the west is good hydrocarbon source rock,the hydrocarbon-generating potential on the edge of the basin is larger than that in the central area of the basin.%对山西沁水盆地石炭－二叠煤系地层烃源岩的有机地化资料进行分析总结。结果表明，山西组和太原组煤岩样品显微组分以镜质组为主，其次为惰质组，稳定组分（壳质组＋腐泥组）的质量分数一般低于11.2％；干酪根 H／C 原子比主要集中在0.20～0.85，O／C 原子比主要集中在0.02～0.10，属高演化Ⅲ型有机质；煤岩碳同位素普遍偏重，为－23‰～－25.6‰；沥青“A”中，饱和烃的质量分数大多数＜25％，芳烃为11％～58％，饱／芳比值一般为＜0.4。煤系泥岩显微组分以镜质组为主，其次是惰质组，壳质组较低；H／C 原子比主要在0.25～0.75，O／C 原子比主要在0.03～0.20，属高演化Ⅲ型有机质，小部分属于Ⅱ2型有机质；碳同位素偏重，为－23.5‰～－25.9‰，饱和烃质量分数＜25％，大部分＜20％。太原组灰岩以Ⅱ2型干酪根为主，碳同位素轻于山西组及太原组煤岩及泥岩，主要在－26.0‰～－30.0‰。制定了适合沁水盆地煤系地层中煤岩和泥岩的生烃潜力评价标准，对烃源岩有利生烃区进行评价。综合认为，沁水盆地山西组煤岩总体上是中等－好烃源岩，以盆地两翼为好，中部和南部为中等－差烃源岩；太原组煤岩总体上为中等－好烃源岩，两翼大部分为好烃源岩，沁县－祁县－榆次－榆社一带以及南部地区为差－中等烃源岩；沁水盆地山西组泥岩总体上为中等偏差的烃源岩，只有西部部分地区为好烃源岩，盆地中部地区烃源岩生烃潜力比两翼差；太原组泥岩总体上为中等偏差的烃源岩，西部局部地区为好烃源岩，盆地边缘比盆地中央的生烃潜力稍大一些。