渤海湾盆地东营凹陷异常压力分布和演化特征及与油气成藏关系

运用数值模拟方法对渤海湾盆地济阳坳陷东营凹陷新生界地层异常压力的分布和演化特征进行研究,结果表明,古近系沙河街组三段和四段地层中广泛发育异常压力,且以超压为主。自沙河街组沉积以来,超压系统开始发育;东营组沉积末期,超压系统逐渐增大。渐新世末喜山运动II幕时期,地层抬升剥蚀,发育负压系统;中新统馆陶组沉积时期,超压系统再次迅速增大;直至明化镇组—第四系沉积时期达到最大范围和最高值。现今凹陷2 200 m以上地层基本为常压,2 200 m以下开始出现明显压力异常。沙河街组高沉积速率导致的欠压实,引发了该时期超压系统的形成,而粘土矿物脱水和烃类大量生成造成了晚期超压系统的发育。结合油气成藏期次研究表明,东营组末期、馆陶组末期及明化镇组—第四系沉积时期,超压系统与凹陷的3期成藏期次具有很好的匹配关系,暗示生烃作用是超压的重要成因,超压又是油气运移的良好动力。

DISTRIBUTION AND EVOLUTION CHARACIERISTICS OF ABNORMAL PRESSURE AND ITS RELATIONSHIP WITH HYDROCARBON ACCUMULATION IN THE DONGYING SAG OF BOHAI BAY BASIN

Numerical simulation method is applied to analyze distribution and evolution characteristics of abnormal pressure system in the Cenozoic Dongying Sag of the Jiyang Depression,the Bohai Bay Basin.The results show that there are extensive abnormal pressure systems in the 3rd and 4th members of Paleocene Shahejie Formation in the Dongying Sag,and they are mainly overpressure ones.Overpressure system has begun to develop since the Shahejie Formation deposits,and increases gradually until the terminal of Dongying episode.In the late Oligocene strata,uplifting and denudation which result from the 2nd episode of Himalaya Movement change the overpressure system into minus-pressure system.After this,fluid pressure of overpressure system increases once more along with the sedimentary period of Guantao Formation in Miocene,and achieves maximal area and maximum in the period of Minghuazhen Formation and Quaternary.At present the normal pressure system locates at the formation above 2 200 m in depth,and the overpressure system is formed at the formation below 2 200 m.High sedimentary rate of the Shahejie Formation makes the development of overpressure system during the early stage,whereas both clay mineral dehydration and hydrocarbon generation result in dramatically rising of fluid pressure of overpressure system since the Late Oligocene.Combined with research conclusion of hydrocarbon accumulation stages,overpressure systems which develop in the terminal of Dongying period,the terminal of Guantao period,and the Minghuazhen-Quaternary period have good relationship with the 3 hydrocarbon accumulation stages of the Dongying Sag.It suggests that hydrocarbon generation is an important reason for overpressure development;meanwhile,overpressure is a favorable power for hydrocarbon migration.