上扬子东南缘下组合优质烃源岩发育及生烃潜力

湘鄂地区海相下组合具良好的油气勘探前景,但地质条件复杂,勘探程度低.咸丰、大庸地区可能烃源岩的系统观测和有机地化剖面研究显示,下寒武统、上奥陶统五峰组—下志留统龙马溪组底部均发育一套黑色页岩,其有机质丰度高,总有机碳含量普遍大于1%;属藻腐泥型,生烃潜力高;具一定规模,厚度达数十米至百余米,分布稳定;有良好的生烃和油气显示,是2套优质烃源岩.晚侏罗世—白垩纪时下寒武统烃源岩已达过成熟早中期生干气阶段,上奥陶统和下志留统烃源岩进入了高成熟晚期至过成熟早期阶段,处于生气高峰期.这2套优质烃源岩的存在,可为湘鄂西、鄂西渝东和雪峰山推覆带等地区下组合的油气生成、成藏提供雄厚的物质基础.

HIGH-QUALITY SOURCE ROCKS IN THE LOWER COMBINATION IN SOUTHEAST UPPER-YANGTZE AREA AND THEIR HYDROCARBON GENERATING POTENTIAL

There are good oil and gas exploration prospect in the southeast of Upper-Yangtze area,but the geologic conditions are complicated and the degree of exploration is low there.The potential hydrocarbon source rocks in Xianfeng and Dayong areas were studied to determine the characteristics of their organic geochemistry,petrology,carbon isotope composition and thermal evolution,etc.Two series of high-quality hydrocarbon source rocks were discovered.They are the Lower Cambrian black shale and the Upper Ordovician Wufeng Formation-Lower Silurian Longmaxi Formation black shale in the Lower Palaeozoic.Both of them have characteristics as follows: 1)good organic types(sapropel type),high(abundance) of organic materials and hydrocarbon potentials;2)large thickness and extensive distribution;3)good hydrocarbon generating potential and evidences of oil(bitumen) and gas.At the Late Jurassic-Cretaceous,the thermal evolution degree of the hydrocarbon source rock in the Lower Cambrian has come to the early stage of over-mature at which the dry gas was generated.And the hydrocarbon source rock in the Upper Ordovician-Lower Silurian has come into the late stage of high-mature to the early stage of over-mature,which was the peak period of gas generation.These high-quality hydrocarbon source rocks provide abundant organic material basis for the hydrocarbon generation and accumulation in the Lower Combination in the west of Hunan and Hubei,the east of Chongqing and the Xuefengshan nappe zone.