东营凹陷岩性油气藏混源相对贡献及石油地质意义

采用地球化学方法,对渤海湾盆地东营凹陷沙三中(E_s3M)岩性型隐蔽油气藏进行了混源相对贡献定量研究。结果表明,牛庄洼陷E_s3M油气藏中沙四段成因原油的贡献约为28%~85%(均值58.5%~67.7%);中央隆起带E_s3M油气藏沙四段成因原油的贡献约为9%~81%(均值32.4%~53.6%)。观察到牛庄洼陷靠近深切断层的原油中沙四段成因原油的贡献量高于远离断层的原油。东营凹陷沙三段砂岩透镜体岩性油气藏中高丰度沙四段"异地源"原油的混源定量结果表明,透镜体岩性油气藏不完全受围岩油源条件控制,隐蔽输导体系与常规运移通道可能联合控制油气运移;透镜体油气藏"自生自储"成藏模式的传统观点有待修正,暗示东营凹陷等断陷盆地生油中心广泛分布的岩性油气藏潜伏着巨大的深部油气勘探潜能。定量结果还表明,牛庄洼陷具备为南斜坡提供足够的沙四段成因成熟油气的条件。东营凹陷沙四段源岩的油气潜能可能需要重新评价。 

Quantitative prediction and significance of mixed oils for lithologic oil pool in the Dongying Depression of the Bohai Bay Basin

Normal geochemical approaches were utilized in quantitative predication of the proportion of the mixed oils derived from Third(E_s3)and Fourth(E_s4) Member of Paleogene Shahejie Formation and accumulated in middle interval of the E_s3(E_s3M) in the Dongying Depression of Bohai Bay Basin,where subtle traps are primarily of lenticular basin-floor turbidite sands encompassed in mudstones mostly developed in the depression.The result shows that about 28%~85% of the mixed oils were derived from the E_s4 interval with averaged level up to 58.5%~67.7% in the Niuzhuang Sag,and about 9%~81% were E_s4 derived oils in the Central Uplift of the depression(the average is up to 32.4%~53.6%).It was observed that there are much more E_s4 derived oils located nearby where deep faults developed.The fact that high concentration of the E_s4 derived oils with long migration distances discovered in the E_s3M subtle lithological traps in the Niuzhuang Sag suggests that surrounding source rocks might be not necessary having a full controlling on hydrocarbons supply of a subtle trap,and subtle migration pathway should play an important role in oil migration.The traditional opinion that hydrocarbons in situ accumulation in lenticular traps with short migration distance from surrounding source rocks should be revised.It is suggested that there is great petroleum potential in the depo-center of rifted basins in Eastern China,and the Niuzhuang Sag is capable to supply normal E_s4 derived oils for the pools in the South Slope,which has been proved by the high proportion of the E_s4 derived oils mixed in the oils of the Wangjiagan Oilfield.The petroleum potential of the E_s4 member in the Dongying Depression should be reevaluated.