Accumulation Characteristics Of Natural Gas Hydrate In Tucuo Area Of Qiangtang Basin

Qiangtang Basin in China has lower temperature,lower geothermal gradient and better hydrocarbon accumulation conditions than Qilian Mountains.From the point of view of hydrocarbon accumulation,combined with relevant geological survey data and previous research results,this study studied the gas source conditions,structural characteristics,mud volcanoes,permafrost and other conditions and characteristics closely related to gas hydrate reservoir formation through field geological survey;By collecting samples and testing,the reservoir-forming conditions of natural gas hydrate in this area are evaluated through hydrogeochemistry,hydrocarbon gas content and fluid inclusion characteristics,and the reservoir-forming characteristics of natural gas hydrate are analyzed based on the existing data of gas hydrate exploration and research.The Triassic and Jurassic strata in the study area are studied in this paper.The strata involved are:Upper Triassic Tumengla Formation,Upper Jurassic Xueshan Formation,Suowa Formation,Middle Jurassic Xiali Formation,Buqu Formation and Jurassic-Lower Jurassic Quemocuo Formation,among which Tumengla Formation,Suowa Formation and Buqu Formation are possible gas source rocks;Through the observation of inclusion transmission light,fluorescence,cathode light and the determination of homogeneous temperature and salinity,it is considered that there are two stages of fault activity accompanied by one stage of oil and gas filling process in the study area.The fault in the study area has strong conductivity to oil and gas migration and is an effective carrier for oil and gas migration and filling;Based on the spatial distribution of potential gas source rocks and the comprehensive evaluation of organic matter abundance,types and maturity of gas source rocks,it is considered that the upper Triassic Tumengla Formation shale in the study area is a potential gas source rock for gas hydrate in the study area;Through permafrost investigation,permafrost is a good capping layer;Two mud volcanic groups were found in the study area,which may be related to basement structure,anticline structure and Quaternary sediment type;The hydrochemical and water isotope geochemical characteristics ofspring water and mud volcanic lake water reflect the good sealing ability of groundwater in the south of Chibuzhangcuo and west of Jiejie river,and the content of ammonium ion also reflects the relatively rich organic matter in the area of Jiejie river and south of Tucuo.