准噶尔盆地陆南地区油气成因

陆南地区侏罗系和白垩系油气勘探获得重大突破，但其油气成因及来源存在争议。采用全烃地球化学方法，对天然气、原油轻烃和生物标志物特征进行分析，并与周缘构造油气特征进行对比，明确了陆南地区油气成因及来源。该区原油碳同位素较轻，轻烃庚烷值和异庚烷值较小，甲基环己烷含量较高，C₂₈甾烷丰度较低，与莫北凸起原油明显不同，与滴南凸起南分支原油和东道3井白垩系储层抽提物特征基本一致；天然气组分和甲、乙烷碳同位素特征与莫北凸起天然气以及典型的石炭系来源天然气均不同。结合区域构造和烃源岩分布特征，指出陆南地区浅层原油和天然气源区均为东道海子凹陷，原油主要为二叠系平地泉组成熟阶段产物，并存在侏罗系源岩成熟阶段产物的混合；天然气主要为石炭系高-过成熟阶段产物，存在二叠系来源的成熟阶段产物的混合。该区下步勘探应往东道海子凹陷延伸，凹陷北斜坡迎烃面大量发育的岩性圈闭和构造-岩性圈闭具有巨大勘探潜力。

Origin and source of oil and gas in Lunan area of Junggar Basin

The origin and source of oil and gas in Jurassic and Cretaceous reservoirs in Lunan area of Junggar Basin remain controversial, despite that great achievements have been made in oil and gas exploration in this area. In this study, the characteristics of natural gas, light hydrocarbons in crude oil, and relevant biomarkers were analyzed by using the method of whole-hydrocarbon geochemistry, and then compared with hydrocarbon characteristics of peripheral structures in order to clarify the origin and source of oil and gas in Lunan area. The crude oil in Lunan area is characterized by light isotopes of carbon, small heptane and isoheptane values of light hydrocarbons, high content of methyl cyclohexane, and low abundance of C28 sterane, which is signifiacntly different from crude oil in Mobei uplift but generally identical with that in the southern branch of Dinan uplift and the Cretaceous reservoir extract in Well Dongdao-3. Additionally, natural gas composition and methane-ethane carbon isotope characteristics of Lunan area are different from those of Mobei uplift and typical Carboniferous reservoirs. Combined with regional structure and source rock distribution characteristics, we propose that shallow crude oil and gas in Lunan area are both derived from Dongdaohaizi sag. Specifically, the crude oil mainly comprises products of mature Permain Pingdiquan Formation, mixed with products of mature Jurassic source rocks; the natural gas mainly comprises products of high-over mature Carboniferous source rocks, mixed with products of mature Permain source rocks. Future exploration in Lunan area should be extended to Dongdaohaizi sag, where there is great exploration potential in the north slope associated with substantial development of lithologic and structural-lithologic traps.