三塘湖盆地二叠系干酪根热模拟气体产物的地球化学特征

Geochemical characterization of gaseous pyrolysates from a Permian kerogen of Santanghu Basin

针对三塘湖盆地的主力烃源岩二叠系芦草沟组泥质烃源岩开展封闭体系和半开放体系热模拟实验，前者将干酪根密封在金管中开展实验、后者直接对烃源岩样品进行压机半开放体系热解模拟，对实验中生成气体的组分和稳定碳同位素进行分析。实验结果显示，两种热解方法以无机气体生成为主，包括CO2、H2、H2S 和 N2等，其中 CO2含量最丰富，这与样品干酪根中丰富的氧含量一致。半开放体系模拟实验温度达到480℃时，气态烃的含量达40.64%，其中甲烷含量达到26.10%，封闭体系中随着模拟温度升高烃类气体产物的碳同位素呈现先变轻后变重的趋势，但同位素分馏程度不大， CH4气体的δ13C 值分布在-40.2‰~-46.6‰之间， C2H6分布在-34.3‰~-38.0‰之间， C3H8分布在-33.6‰~-36.0‰之间，而CO2气体δ13C值分布在-32.8‰~-28.8‰之间。三塘湖盆地针对气藏的勘探已经有所发现，但有关气藏的地球化学特征报道较少，该工作中的模拟实验结果可为三塘湖盆地深入的气藏地球化学勘探提供基础数据。

This work was carried out to study the geochemical characteristics of gaseous pyrolysates from Permian argillaceous source rocks of Santanghu Basin, from the closed and semi-open systems, respectively. Kerogens prepared from the source rocks were sealed into golden tubes for the closed-pyrolysis, while the source rocks were used directly for the semi-open system. The composition and stable carbon isotope of the gas generated were analyzed. The results show that, for both pyrolysis systems, inorganic gas were the main products including CO2, H2, H2S, N2. The proportion of CO2 was the highest due to the abundant oxygen content in the kerogens; for the semi-open system, the relative percentage of gaseous hydrocarbons can be up to 40.64%, and the relative percentage of methane is as high as 26.10% when the temperature reaches 480 ℃. With the increasing temperature, the stable carbon isotope ratios of gaseous hydrocarbons from closed system first become lighter and then heavier, with the δ13C of CH4 ranging from -40.2‰ to -46.6‰, C2H6 -34.3‰--38.0‰, C3H8 -33.6‰--36.0‰ and CO2-32.8‰--28.8‰. Gas reservoir has been found in the Santanghu Basin, NW China, but little have been reported on the geochemical characteristics of the gas. Basic data are provided in this work for further petroleum exploration of the Santanghu Basin.