银额盆地居延海坳陷原油物理化学特征与油源探讨

居延海坳陷的吉格达、天草、路井等次级凹陷原油物理、化学特征分析表明，原油物理特征以轻质-挥发性原油为主，个别井产凝析油，具有低粘度、中凝固点的特点。原油化学特征具有饱和烃含量高（78.06%~92.95%），全油碳同位素轻（δ13CPDB为-33.7‰~-32.0‰），轻烃/重烃（∑nC21-/∑nC22+）显著大于1（1.28~2.94）等特点。原油物理、化学特征指示其母质以低等水生生物为主，热演化程度为成熟-高成熟。在对钻井揭示的烃源岩及邻区地表剖面烃源岩分析的基础上，以吉格达凹陷蒙额参3井晚石炭世侵入岩和中—下二叠统2个产层为代表，开展了油-源生物标志化合物及碳同位素分布对比。结果表明，原油与上石炭统—下二叠统干泉组上段烃源岩具有良好的亲缘关系，与白垩系烃源岩无关，原油母岩为石炭系—二叠系烃源岩。依据原油指示的母岩演化程度显著高于钻井揭示的烃源岩演化程度，认为区内油气存在深层（干泉组下段）烃源岩的贡献。综合分析认为，居延海坳陷已揭示的油气藏为石炭系—二叠系含油系统，应将其作为主要勘探目的层。

The physical and chemical characteristics of crude oil and oil-source of Juyanhai depression in Yingen-Ejina Basin

An analysis of physical and chemical characteristics of crude oil of Jigeda, Tiancao and Lujing sag in Juyanhai depression shows that the crude oil is mainly light- volatile oil, condensate is produced in individual wells, and the physical characteristics of the crude oil are low viscosity and medium freezing point.The chemical characteristics of crude oil are highly saturated hydrocarbon(78.06%~92.95%), light isotope of the whole oil(δ13CPDB from-33.7‰ to -32.0‰)and the ratio significantly greater than 1 of light hydrocarbon to heavy hydrocarbon(∑nC21-/∑nC22+ from 1.28 to 2.94).The physical and chemical characteristics show that the parent material is mainly low aquatic organism, and the thermal evolution degree is mature-high mature.Based on an analysis of the source rocks of the surface profile of the adjacent area and the source rocks revealed by wells, the authors made a comparative study of the biomarkers of oil and source rocks as well as carbon isotope, represented by two oil production zones of late Carboniferous intrusive rocks and middle-lower Permian of Mengecan 3 well in Jigeda sag.The results indicate that the crude oil has good relationship with Carboniferous-Permian hydrocarbon source rocks, but it is not related to Cretaceous source rocks, and hence the parent rocks of crude oil are surely Carboniferous-Permian source rocks.Then according to the fact that the evolution degree of the parent rocks indicated by crude oil is significantly higher than that of the source rocks revealed by wells, it is believed that there is the contribution of the source rocks in the deep layer(lower Ganquan Formation).The comprehensive analysis shows that the revealed oil and gas reservoir is a Carboniferous-Permian petroliferous system in Juyanhai depression, which should be taken as the main exploration target.