青海乌丽冻土区冷泉水溶烃对形成天然气水合物的指示意义

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

针对深处青藏高原腹地中低纬度高海拔（4 600~5 300m）永冻土地带的青海乌丽地区,开展了该地区天然气水合物形成的气源条件研究。冻土区地表沿断层发育若干冷泉,野外采集冷泉新鲜水500mL密封送实验室进行气相色谱分析。首先对水中溶解的烃在真空和60℃恒温条件下脱出气体,将脱出气体经ρ（NaOH）=300g/L的碱液吸收CO2,余下气体经碱液驱赶至量气管上端,计量脱出气体的体积,并转移至另处;然后根据溶解烃含量注入适当体积的脱出气体进行色谱标定、单点外标定量。结果在冷泉中检测出CH4体积分数一般在223.60~1 097.30μL/L之间,最高达1 113.21μL/L。野外工作查明烃源岩主要为上二叠统那益雄组含煤碎屑岩建造,次为上三叠统巴贡组碎屑岩。前者中赋存的煤层及炭质泥岩为天然气水合物气源供给的重要母质。此研究成果揭示该地区具备形成天然气水合物藏的良好气源条件及成藏潜力。

Wuli permafrost is located in the Qinhai-Tibetan Plateau, with low latitude and high elevation （4 600--5 300 m）. 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 chromatogra- phy 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）=300 g/L alkali liquor, while the remaining gas was expelled through the lye to the upper airway, ana transIerrea to anomer place altcl tile 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. 30μ/L, up 1 113.21 μl/L. The favorable source rocks are mainly Late Permian Nayixiong Group of interactive marine and terrestrial coal-bearing elastics and the Late Triassic elastics 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. Results of this study suggest that the region has potential conditions for the gas hydrate entrapment and accumulation.