青海木里冻土区煤系烃源岩饱和烃地球化学特征

摘要

随着天然气水合物的发现，祁连山冻土区成为勘探研究重点区块。通过系统的野外露头采样，在进行有机碳测试、镜质体反射率等常规地球化学分析的基础上，运用气相色谱-质谱分析技术，探讨了研究区烃源岩有机质的母质来源、沉积环境以及热演化程度。研究结果表明：研究区样品热演化程度均较高，主要处于高成熟阶段，且C25四环萜烷可能是研究区潜在的有机质高演化阶段特征性标志物。样品母质来源为陆源高等植物与低等水生生物的双重贡献。泥岩姥植比小于1.0、伽马蜡烷值小于0.2，形成于淡水还原环境；而煤样姥植比大于1.0，主要形成于偏氧化环境，以高等植物贡献为主。结合研究地区的沉积相，石炭系、二叠系主要为海陆交互相，侏罗系为湖沼相沉积，煤样可溶烃的生物标志物同样反映这一变化特征。%Qilian Mountain permafrost has been the main exploration region since samples of gas hydrate have been drilled.Based on the analysis of organic carbon content and vitrinite reflectance measurement, combined with GC-MS, the organic source, depositional environment and thermal maturity of hydrocarbon source rocks were sys-tematically discussed.The results show that samples of the study area stay in a high mature stage during the thermal evolution.The C25 tetracyclic terpane may be an indicator which reflects organic matters with high maturity in the study area.Lower aquatic organisms mixed with higher terrigenous plants are proven to be the organic material of hydrocarbon source rocks.The Pr/Ph value ( <1 ) and gammacerane/C30 hopane value ( <0.2 ) of coal-measure mudstones indicate that source rocks are developed in a fresh water-reductive environment.High Pr/Ph ratio illus-trates these coals, derived from higher terrigenous plants, formed in oxygenated conditions.The coals in the Car-boniferous and Permian are deposited in a marine-terrestrial environment.However, coal in the Jurassic mainly formed in lacustrine-swamp facies.Biomark analysis of soluble hydrocarbon in coals, combined with the sedimenta-ry facies of study area, was illustrated the same characteristics.