辽中凹陷JZ20-A构造油气成藏特征

辽中凹陷分布有4套烃源岩,东营组二段下亚段、东营组三段、沙河街组一段与沙河街组三段,除东营组二段下亚段多处于未-低熟阶段外均为有效烃源岩。辽中凹陷北洼和自身的沙河街组三段烃源岩为JZ20-A油气田的主要供油区和油气来源。沙河街组三段烃源岩生烃潜力大,有机质丰度和成熟度较高。通过JZ20-A井主要产层段的包裹体分析,确定了JZ20-A油气田的油气成藏期次,建立了JZ20-A油气田的油气成藏模式。研究结果表明,包裹体均一温度分布于120～140℃。油气的主要充注期在距今5 Ma以来明化镇组沉积末期,在东营组沉积时期(约27 Ma)也有少量的油气充注。JZ20-A各油气藏充注程度高,包裹体GOI值(含油流体包裹体丰度指标)均大于5%。油气成藏表现为接力供烃,高压泥岩双重封堵,油气叠层式成藏的特征。

Characteristics of hydrocarbon accumulation in JZ20-A structure in Liaozhong Sag

The lower 2nd member and 3rd member of the Dongying Formation,the 1st and 3rd member of the Shahejie Formation are four source rocks in Liaozhong Sag.The latter three are active source rocks,but the lower 2nd member of the Dongying Formation is immature to lowly mature.The 3rd member of the Shahejie Formation in the northern subsag of the Liaozhong Sag is the main source rocks for the JZ20-A oilfield.The source rocks in the 3rd member of the Shahejie Formation are of high organic content and maturity,thus have great potential for hydrocarbon generation.By analyzing the inclusion of the major pay zones in the well JZ20-A,we performed the timing of the hydrocarbon generation and established the hydrocarbon accumulation model in the JZ20-A oilfield.The results indicate that the homogenization temperature of the inclusion is 120-140 ℃.The hydrocarbon charging mainly occurred at 5 Ma ago when the Minghuazhen Formtion was deposited.Hydrocarbon charging also happened at 27 Ma ago when the Dongying Formation deposited.All the reservoirs of JZ20-A oilfield are high in hydrocarbon abundance.The GOI value of the inclusion is above 5%.The characteristics of the hydrocarbon accumulation are relay-type multiple stage hydrocarbon charging,over-pressured shale sealing on both sides and oil/gas accumulation in superimposed multiple layers.