Implications of Soluble Hydrocarbons in Cold Spring Water on the Formation of Gas Hydrate in Wuli Permafrost,Qinghai Province

Wuli permafrost is located in the Qinhai-Tibetan Plateau,with low latitude and high elevation(4 600-5 300m).This paper describes the study of the gas source conditions for gas hydrate formation in the area.Several cold springs(Reisen)are developed along the fault in the permafrost area.For the study,500 ml fresh water of the cold springs was collected,sealed and sent to the laboratory for gas chromatography analysis.First of all,gas in the dissolved hydrocarbon was extracted in vacuum and 60℃ constant temperature conditions,and CO₂ was absorbed by ρ(NaOH)=300g/L alkali liquor,while the remaining gas was expelled through the lye to the upper airway,and transferred to another place after the volume was measured.Then appropriate volume of prolapse is injected into the dissolved hydrocarbon according to its content,and calibrated chromatography,a single point external standard quantification.It is detected in the result that the CH₄ content in cold spring water is generally around 223.60-1 097.30 μl/L,up 1 113.21 μl/L.The favorable source rocks are mainly Late Permian Nayixiong Group of interactive marine and terrestrial coal-bearing clastics and the Late Triassic clastics of Bagong group.Multiple coal seams and dark carbonaceous shale contained in the former strata are considered to be the important parent materials for the gas hydrate formation.Resultsof this study suggest that the region has potential conditions for the gas hydrate entrapment and accumulation.