Geologicl Conditions Of Shale Gas Formingof Niutitang Formation In Northwest Hunan

China has a large number of unconventional oil and gas resources,according to preliminary estimates,the total amount of shale gas resources in China is similar to the UnitedStates,which has a well potential of exploration and development.The geological forming conditions of shale gas in northwestern of Hunan Province is good.On the basis of predecessors,guided by sedimentology and reservoir geology,taking the organic shale layer of Niutitang Formation in the Lower Cambrian as the research object and the route geological survey and the profile measurements as the main means,a series of indoor test analysis were carried out.Combined with the drilling and logging data,fully absorb the experience of exploration and development to determine shale position,buried depth,thickness and distribution,and through geochemical test and analysis,the organic geochemical,rock mineralogical characteristics,reservoir properties and accumulation conditions in the Lower Cambrian Niutitang Formation can be available.On this basis,the reservoir distribution pattern in the study area is generalized,so as to analyze the potential of shale gasand find out the favorable exploration area.Basin-deep shelf shallow-continental shelf sedimentary system was developed in Niutitang Formation in the study area.The dark shale mainly developed in the basin-deep shelf environment and it is mainly composed of black siliceous rocks,siliceous shale and carbonaceous shale.The distribution for the black shale of Niutitang Formation in Northwest Hunan is wide,and it has stable thickness in the region.The thickness of the two high value area is respectively Laifeng-Longshan area and Linli-Changde area.Depth of shale in Niutitang Formation in the region varies greatly,which is generally 500 to 4500 meters,in most areas more than 2000 meters.The average content TOC for the black shale of NiutitangFormation in Northwestern Hunan is 3.08%.Vertical,high-quality shale concentrated in the middle and lower section.Xianfeng and Yuanling area has two TOC high value at plane,which is over 6.0%.The type of organic matter is I type organic matter.Organic matter is in the stage of over mature evolution of organic matter,Ro is over 2.5%.The black Shale of Niutitang Formation in Northwestern Hunan has the characteristics of low porosity and ultra low permeability.The types of shale reservoirs in the study area can be divided into 3 types: Organic pores,inorganic pores and micro fractures.The mineral composition is mainly composed of quartz and clay minerals,followed by calcite,Containing a small amount of feldspar,dolomite,pyrite,etc.The average content of quartz is 62%,and the higher brittle mineral is beneficial to later fracturing.The main component of clay minerals are illite,illite smectite mixed layers,chlorite,and kaolinite,not containing smectite.The characteristics of clay minerals indicate the high degree of shale evolution in this area.According to the shale gas definition standards released by the Ministry of land and resources,and the Department of energy,combined with the gas-bearing shale's size,thickness,maturity,depth,content,surface and preservation conditions,a plurality of favorable zones of shale gas are selected according to the horizon.MainlyCili-Yongshun-Zhangjiajie panhandle region,Longshan area and northwestern Shimen.