渤海湾盆地渤中凹陷渤中19-6构造凝析油气特征与形成机制

基于凝析油和天然气组分、生物标志化合物、稳定碳同位素和储层流体包裹体等分析结果,综合运用多种油气地球化学方法,明确了渤海湾盆地渤中凹陷西南部渤中19-6构造中凝析油和天然气的特征及成因,探讨了油气的形成机制。研究结果表明,渤中19-6构造的凝析油具有低密度、低黏度、低胶质+沥青质、高蜡和高凝固点的物性特征,其正构烷烃以中—高碳数为主,轻烃组分以正辛烷、正庚烷和甲基环己烷为主且含量相当,为沙河街组三段烃源岩成熟阶段的产物。天然气组分主要为烃类气,非烃气体含量低,为沙河街组三段偏腐殖型烃源岩裂解气。12 Ma以来,渤中19-6构造经历了重质油、轻质油气、凝析油气和天然气的多幕连续充注。相控混溶为渤中19-6构造中凝析气的主要形成机制,即在含原油的天然气流体中,当地下温度、压力升高时,早期原油溶于晚期充注的天然气中,形成现今的凝析气藏。

The characteristics and formation mechanism of condensate oil and gas in Bozhong19-6 structure,Bozhong sag,Bohai Bay Basin

Based on the analysis results of condensate oil and gas components, biomarkers, stable carbon isotopes and fluid inclusions, compressively using mulitple research methods of petroleum geochemistry, this paper determines the characteristics and genisis of condensate oil and gas and explores the oil-gas formation mechanism in Bozhong19-6 structure, southwestern Bozhong sag, Bohai Bay Basin. The results show that the condensate oil has physical properties of low density, low viscosity, low colloid and asphaltene, high wax and high freezing point. In the condensate oil, n-alkanes are mainly composed of medium and high carbon components, and light hydrocarbon components are dominated by the n-octane, n-heptane and methylcyclohexane with the same contents. The condensate oil is the product of mature source rocks in Member 3 of Shahejie Formation. The natural gas is mainly composed of hydrocarbon gas with low content of non-hydrocarbon gas and derived from the cracking of humic-type source rocks in Member 3 of Shahejie Formation. The Bozhong19-6 structure has experienced multi-stage continuous charging of heavy oil, light oil, condensate oil or gas, and natural gas since 12Ma. The phase-controlled miscibility is the main formation mechanism of condensate gas in Bozhong19-6 structure. In the natural gas fluid containing crude oil, the early crude oil dissolves in the later charging natural gas with the increase of underground temperature and pressure, thus forming the present condensate gas reservoir.