Study On Shale Gas Of Lower Permian Longtan Formation In Xiangdongnan Depression

The Xiangdongnan depression， a relatively low degree of exploerationdepression,is located in the southeast of the Hunan province, where a very importantarea that studying for the shale gas of the south. And the Longtan formation, which hasa well-development shale, is a marine shale formation as important as the Longmaxiformat ion， Doushantuo formation and Wufeng formation. It has a better geologicalcondition for shale gas, and favorate for the shale gas exploration. This paper focus onthe characteristics and geological conditions of the shale of the longtan formation inXiangdongnan depression, thus to predict its exploration prospects.The longtan strata were mainly deposited in marsh and bay lagoon face, and itsinterval is dominated by fine-grained sediment,comprised of gray and black siliceousshale, black carbonaceous shale, sandy mudstone and muddy sandstone. The shalesystem contain a large number of fossils. The source area are Luoxiao(paleo-)land andanran uplift.Youxian to Chaling to Anren, Leiyang to Yongxing to Chenzhou and Linwu toYizhang are defined to have high quality source rock,with better abountant of organiccontent,dominated byⅠ-Ⅱ types of kerogen. There exsits three high thermal maturityzones in the area, such as hengdong to anren to chaling, leiyang to yongxing, yizhangto linwu.The clay mineral content is less than40%in Longtan formation, and have a higherproportion of carbonate minerals. Reservoir and flow space is mainly constituted bypores and cracks. Pore type include intergranular porosity, intragranular porosity andorganic matter holes. The mainly contain large wear layer cracks, small cracks andmicro cracks. The nanometer to micron level microporosity is beneficial for porosityand permeability of the shale. The adsorption simulations can better reflect shaleadsorption chatacteristics. The experimental data shows that the shale sampleadsorption is1.60cm3/g, the study suggest that the internal factors that affect theadsorption content mainly contain toc, the organic matter type and maturity, clay content, pore development and water content. The main external factors containthickness, depth of the temperature and pressure condition.The longtan formation have a good hydrocarbon condition, and have betterorganic matter content as the coal-bearing strata with wide distribution and moderateburial depth. With comprehensive analysis from oil and gas source condition, reservoircondition, storage condition and construction condition, we find three areas(includeyouxian to chaling, leiyang to yongxing and linwu to yizhang) that suitable for the shalegas study. Meanwhile, leiyang to yongxing area is the best, linwu to yizhang is thesecond and youxian to chaling is the third.