A Comparative Study On Shale Gas Geological Character Of Longmaxi And Niutitang Formations In South China

This dissertation is granted by China Geological Survey project “Application of geochemistry technologies to shale gas survey” conducted by the National Research Center for Geoanalysis(NRCGA).In recent years, more and more attention has been paid to the exploration and development of shale gas, so shale gas survey has become an important direction of the development of energy industry in China, the cumulative production of shale gas of China in 2013 is up to 200 million cubic meters, and it exceeded 1 billion and 500 million cubic meters in 2014. The favorable areas of shale gas distribution in China are mainly subdivided into 4 regions: the southern China,the northern China, the northwestern China, and Qinghai-Tibet Plateau, accounts for 46.8%, 8.9%, 43% and 1.3%of the total recoverable resources, respectively. The shale gas resources of the Paleozoic, Mesozoic and Cenozoic accounts for China’s total shale gas resources amount 66.7%, 26.7% and 6.6% respectively. So the Paleozoic strata in southern China become the key horizons for shale gas. Especially the Formations Niutitang and Longmaxi, the southern marine shales, are well developed. By the previous study of the two sets of hydrocarbon source rocks, it has been found that the two Formations have little difference from each other. However, the shale gas production in the Formations have big differences: the industry shale gas can be available in Longmaxi Formation, whereas the industry shale gas is absent in the Niutitang Formation. How about the shale gas’ prospect in the Niutitang Formation? The research object of this thesis is Chinese South Niutitang Formation and Longmaxi formations. Through the field observation of 13 Sections,Rock-Eval, the total organic carbon determination,identification of rock section, etc. We have a preliminary understanding of the organic geochemical characteristics of the two sets shale in Yangtze plate. On the basis of this,we selected two sections for further comparative analysis. We make a key research of the Qilongcun section(Longmaxi Formation),Wenshuicun Section(Niutitang Formation). Observed by microscope, scanning electron microscope(SEM), whole rock analysis with X-ray diffraction, X-ray diffraction of clay minerals analysis, experiment of mercury porosimetry, nitrogen adsorption test, kerogen carbon isotopic analysis and isothermal adsorption experiments, combined with field observations and previous on sedimentary environment study,we conduct a systematic comparison of Longmaxi and Niutitang formation respectively from the sedimentary characteristics, shale gas, storage, cover conditions etc. Through a series of experimental data show that the Niutitang formation has a high organic matter content than the Longmaxi shale, but has a high organic matter maturity, and relatively less brittle mineral content, high content of clay minerals than Longmaxi formation shale and it sreservoir characteristics are not good than Longmaxi shale, so Niutitang Formation is not conducive to the accumulation of shale gas reservoir than Longmaxi Formation. Because of the difference of Longmaxi Formation and Niutitang Formation at the top and bottom rocks. It is found that the Niutitang Formation shale is not conducive to the preservation of shale gas, which also resulted in the Niutitang Formation shale has a poor condition to storage shale gas than Longmaxi Formation.