Potentiality Analysis Of Black Rock Series Of Longtan Formation In Jiangsu And Zhejiang, Anhui Provinces

The world is gradually marching towards a severe energy crisis and consequently, there is growing concern for the research and exploration on unconventional petroleum resources, among which the evaluation on the potential and target areas of shale gas is a currently important work. In this study, we studied the shale gas potential and corresponding target area in Jiangsu, Anhui and Zhejiang provinces based on structural geology, organic petrology and organic geochemistry. We investigated the structural characteristics, distribution and occurrence of source rocks in this region and proposed the sedimentary environments and reservoir property of the Longtan Formation, Upper Permian. Our observations suggested that Jiangyin-Wuxi and Gangkou-Yishan areas show great shale gas potential.The Lower Yangtze region has experienced three evolutionary stages in Paleozoic, including passive margin basin, foreland basin and Intra-Cratonic basin and was then strongly modified by thrust nappe and extentional rift during Indosinian-Early Yanshan and Late Yanshanian stages, respectively. The study area can be divided into the southern Jiangnan fold belt and Northern fold-depression zone based on the the gravity and magnetic characteristics, and the investigations on outcrops and seismic sections; the fold-depression zone can be subdivided into eight secondary tectonic units.The black mudstone in Longtan Formation of Upper Permian belongs to paralic delta phase and serves as an important source rocks in the study area. The reservoir rocks in the Longtan Formation are mainly composed of silty mudstone, mudstone, siltstone and coal. The brittleness of the balck mudstones increases from Taihu area to sourthern Anhui Province. The thickness of the dark rock series increases form west to east and shows four mudstone-rich areas.In general, the coal measures in the Longtan Formation is rich in organic carbon; the concentrations of the total organic carbon (TOC) are6.13,4.98, and3.3%at southern Jiangsu Provinece, southern Anhui Province and northwestern Zhejiang Province, respectively. However, differences exist in the organic matter type; the organic matter type of bark coal is Type Ⅱ, whereas the organic matter type of the other coals and mudstones is Type Ⅲ Most of the study area shows a high thermal evolution degree with a degree of high mature to overmature.but there are two belts showing a low-medium thermal evolution degree.The study area shows a great shale gas potential based on the comprehensive analyses on structural features, distribution of source rocks and the thermal evolution degree. We propose that the target areas mainly distribute in the Changzhou-Xuancheng rift basin, synclinorium of Jiangyin-Suzhou detachment fold belts, as well as the Gangkou-Yishan area in the Nanling-Jurong rift basin, the last two of which have the best condition for petroleum generation and preservation.