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(δ¹³C_PDB from-33.7‰ to -32.0‰)and the ratio significantly greater than 1 of light hydrocarbon to heavy hydrocarbon(∑nC_21-/∑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.