北黄海盆地东部坳陷中生界烃源岩特征及其指示的油气勘探方向

Characteristics of Mesozoic Source Rocks and Exploration Direction of Oil and Gas in the Eastern Depression, North Yellow Sea Basin

为了量化表征北黄海盆地东部坳陷中生界主力烃源岩生、排烃特征,综合利用镜质体反射率(Ro)、残余有机碳含量(TOC)、岩石热解、干酪根镜检及饱和烃色谱等资料,在总结研究区烃源岩地化特征的基础上,通过油源对比明确主力烃源岩层并依托盆地模拟方法量化其生、排烃贡献.结果表明,北黄海盆地东部坳陷中生界的两类原油均来源于区内中侏罗统和上侏罗统两套主力烃源岩层,其中,中侏罗统烃源岩的有机质丰度整体处于"好-最好"级别,上侏罗统烃源岩的有机质丰度则以"中等-好"为主;二者均存在早白垩世末期和早中新世两次生、排烃高峰,但上侏罗统的排烃速率[qe(max)=27.3×106t/Ma]远高于中侏罗统的排烃速率[qe(max)=4.2×106t/Ma],对研究区油气成藏的贡献更大.虽然下白垩统暗色泥岩的生烃潜力有限,但其底部砂岩与紧邻上侏罗统主力烃源岩层构成的"下生上储"式的源储配置关系是区内最重要的勘探目的层,其次为中、上侏罗统内部"自生自储"式的有利成藏组合,同时,中侏罗统下部"上生下储"式的成藏组合也应予以重视.

In order to quantify the characteristics of hydrocarbon generation and expulsion of Mesozoic main source rocks in the eastern depression of the North Yellow Sea Basin,geochemicalcharacteristic of the Mesozoic source rocks in this study area was summarized by comprehensively using vitrinite reflectance(Ro),residual organic carbon(TOC),rock pyrolysis,kerogen microscopic examination and gas chromatographic analysis of saturated hydrocarbons and other geological data.Then on the base of these,this paper has clearly defined the chief source rocks through oil-source correlation and furtherquantified the contribution of hydrocarbongeneration and expulsion.The results show that two types of Mesozoic crude oil in eastern depression of the North Yellow Sea Basin are all originated from the two chief source rocks of the Middle Jurassic and Upper Jurassic.Among them,organic matter abundance of the Middle Jurassic source rocks is in the"good-best"level,while that of the Upper Jurassic source rocks is mainly in the"medium-good"level.The two sets of source rocks all have two peaks of hydrocarbon generation and expulsion in the Early Cretaceous and Early Miocene.However,the hydrocarbon-expulsion rate of the Upper Jurassic source rocks[q(emax)=27.3×106 t/Ma]is much higher than that of the Middle Jurassic source rocks[qe(max)=4.2×106 t/Ma],which has the most important contribution to the hydrocarbon accumulation.Although the hydrocarbon generation potential of dark mudstones in the Lower Cretaceous is limited,the source-reservoir matching relationship between the bottom sandstone of the Lower Cretaceous and the chief source rocks of the Upper Jurassic is"lower generation and upperaccumulation",which is the first exploration target in this study area.The secondary target layer is the reservoir forming combination of"self generation and self accumulation"in the Middle and Upper Jurassic.And the reservoir combination of"upper generation and lower accumulation"in the lower part of the Middle Jurassicis also noteworthy in oil-gas exploration.