准南前陆盆地玛纳斯背斜油气动态成藏过程

Dynamic hydrocarbon accumulation process in Manasi anticline in the southern Junggar foreland basin

玛纳斯背斜是准噶尔盆地南缘前陆盆地的典型含油气构造,随着油气勘探开发工作的不断深入,复杂的油气特征及来源问题使其成藏过程亟待准确剖析。为此,应用流体包裹体、储层沥青显微观察、储层定量颗粒荧光测试等技术手段,结合多种油气地化参数分析资料,剖析了该区油气成藏期次与动态成藏过程。结果表明:①玛纳斯背斜主要存在2期成藏,第一期成藏时间在距今11Ma左右,以源自下白垩统吐谷鲁群湖相烃源岩的中低成熟原油充注为主,并形成一定规模的古油藏,第二期成藏时间在距今3Ma左右,以源自中下侏罗统煤系烃源岩的天然气充注为主,伴随下白垩统较高成熟度原油充注;②后期大量高成熟天然气的注入导致原古油藏发生"气侵分馏"作用,并逐渐改造形成现今的凝析油气藏,与此同时,伴随"气侵分馏"作用的进行,古油水界面在保持古油藏布局的基础上经过后期的逐渐向上调整,形成了现今的气水界面。结论认为:玛纳斯背斜油气藏经历了2期成藏,表现出"早油古藏,晚期气侵"、改造调整的动态演化特征。

The Manasi anticline is a typical oil-bearing structure in the southern margin of the Junggar foreland basin. It is urgent to accurately understand the hydrocarbon accumulation process, so as to provide solid foundation for further exploration and development in this study area. Various methods such as fluid inclusion analysis, microscopic observation of reservoir bitumen, and quantitative grain fluorescence tests were used to perform the timing of hydrocarbon accumulation and to determine the dynamic hydrocar bon accumulation process. The hydrocarbons in the Manasi anticline were mainly accumulated in two stages. The first stage was at about 11 Ma when charging of the moderate-low mature crude oil from the lacustrine source rocks in the Lower Cretaceous Tugulu Group was predominant, leading to the formation of ancient oil pools with certain scale. The second stage was at about 3 Ma, when charging of gas from the Middle-Lower Jurassic coal measure source rocks was predominant and accompanied by charging of some highly mature crude oil from the Lower Cretaceous source rocks. The large scale charging of highly mature gas at the late stage caused ＂gas washing fractionation＂ of the preceding ancient oil pools, leading to the formation of present existing condensate gas reservoirs. Meanwhile, the ancient oil water contact moved up progressively in the late stage, resulting in the present gas-water contact. In conclusion, the hydrocarbon reservoirs in the Manasi anticline going through a dynamic evolution process have experienced two stage accumulation of early paleo oil pool and late gas washing.