Study On Formation Conditions And Influencing Factors Of Gas-bearing Characteristics Of Shale Gas

Western HuNan is a very important area that studying for the shale gas ofthe south, where the shale is well-development, has a relatively low degree of exploration depression. This paper focus on formation conditions and influencing factors of gas-bearing characteristics of Niutitang formation of western HuNan, and give a comprehensive evaluation of gas-bearing characteristic, eventually optimizes the favorable blocks of shale gas exploration.The bottom of the Niutitang formation has a conformable contact with the Liuchapo formation in upper sinian, and the top has a conformable contact with the Palang formation in lower Cambrian, The Niutitang formation were mainly deposited in deep water shelf face, and its interval is dominated by black carbonaceous shale, siliceous shale, and silty shale.The dark shale of Niutitang formationis 40～150m thick, the TOC is higher, generally higher than 2%, dominant with Ⅰ-Ⅱ types ofkerogen. The Ro of source rock ranges from 2% to 3.5%, which means the organic matter stays in high-over maturity stage, and the Ro is show the gradually increasing from northeast to southwest.The shale is mainly composed of quartz and clay minerals, the content of illite in clay minerals is higher,which is favorable to the gas adsorption.And the physical properties of shale is favorable, has a certain specific surface area and porosity, the pore types can be divided into intergranular porosity,intragranular porosity, organic matter holes and fractures.The research area experienced tectonic movement of multiple period since Paleozoic, and parts of the tectonic movement was later than the peak of the gas generation of the Niutitang shale, which greatly influenced the preservation condition of shale gas. And parts of the Niutitang shale were buried shallow, which was not benefit for the preservation condition. In addition, the formation water condition is not favorable, the salinity is lower, and the water is NaHCO3type.The Niutitang formation has a certain gas-bearing characteristics, the gas content of Changde-1 well is range from 0.26 to 2.81m3/t, and the maximum adsorption of the isothermal adsorption is between 0.5 to 4.26 m3/t. Analysis the influencing factors of the gas-bearing characteristics, consider that the gas content is related to the organic carbon content, kerogen type, thermal maturity, clay mineral content, quartz content and preservation conditions.From the generation condition, reservoir condition and preservation conditions, give acomprehensive evaluation of gas-bearing characteristics ofNiutitang formation, optimizes Xiushan-Huayuan, Sangzhi-Shimen, Changde-Linli,Jishou-Guzhang, Tongren-Songtao, Longshan-Yongshun as the favorable blocks of the gas-bearing characteristics,combining the further development conditions, eventually optimizes Xiushan-Huayuan,Sangzhi-Cili, Changde-Linli, Tongren-Songtao, Longshan-Yongshun asfavorable blocks of shale gas exploration. Then give a comprehensive evaluation for the key block, calculated the shale gas resource.