渤海湾盆地黄河口东洼优质烃源岩发育控制因素

Controlling factors for the development of high-quality source rocks in Yellow River mouth east sag of Bohai bay basin

通过对黄河口东洼古近系3套烃源岩的岩石热解、抽提物饱和烃、芳烃(GC/MS)分析,研究烃源岩的地球化学特征,指出优质烃源岩发育层段,并对其形成的控制因素进行分析。结果表明:黄河口东洼沙三段、沙一二段和东下段存在有机质丰度高、类型好、生烃能力强的优质烃源岩。其中沙三段烃源岩厚度大,有机质丰度最高,类型最好,主要为Ⅱ1和Ⅰ型,且已进入生烃门限,优质烃源岩最为发育;沙一二段烃源岩次之,有机质丰度较高,类型较好,主要为Ⅱ1型,优质烃源岩较为发育;东下段烃源岩相对较差,有机质丰度主要达到好烃源岩的标准,有机质类型主要为Ⅱ2型,有机质丰度和类型相对前两者差一些。构造和古气候、湖盆古生产力及有机质保存条件控制烃源岩发育,沙三段沉积时期气候炎热湿润,大量的藻类输入形成较高的生产力水平,半深湖—深湖还原环境使有机质的保存条件良好,有机质含量整体较高。沙一二段沉积时期气温有所降低,藻类勃发,具有较高的古生产力,低Pr/Ph、高伽马蜡烷/C30藿烷反映水体盐度较高,沉积环境为缺氧的强还原环境,对有机质的保存极为有利。东下段沉积时期气候温暖半湿润,母质来源构成上以混源为主,但陆源高等植物输入更多,沉积环境主要为淡水还原环境,总体上古生产力水平和有机质保存条件相对前两者较差,整体有机质含量偏低,有机质类型偏差。

Based on rock pyrolysis analysis and Gas Chromatograph-Mass Spectrometry(GC/MS)of saturated and aromatic hydrocarbon on three sets of hydrocarbon source rock samples in Yellow River mouth east sag,the geochemical characteristics of theses source rocks have been studied,the intervals of high-quality source rocks have been identified and the controlling factors have been analyzed.Research shows that there are high-quality source rocks with high abundance of organic matter,good organic types and strong hydrocarbon-generation potential in all E_2s_3,E3s1-2and E3dLin Yellow River mouth east sag.Of these,source rocks in E_2s_3have large thickness,maximum abundance of organic matter and best organic types(mainlyⅡ1andⅠ),what is more,they have reached hydrocarbon generation threshold,thus high-quality source rocks are best developed.Source rocks in E3s1-2come second.They have high abundance of organic matter,good organic types(mainlyⅡ1),thus high-quality source rocks are well developed.Source rocks in E3dL,whose abundance of organic matter has mainly achieved good quality standards and main organic type isⅡ2,are relatively poorly qualified.Compared to the former,their abundance of organic matter and organic matter types are worse.The development of source rocks is controlled by tectonics,paleoclimate,productivity of basin and preservation condition for organic matter.Due to hot and humid climate during sedimentary period,high level of productivity contributed by massive input of algae and good preservation condition for organic matter with semi deep-deep lake reducing environment,source rocks in E_2s_3 have relatively high organic contents on the whole.While E3s1-2 was deposited in a period with lower air temperature and algal blooming,so its source rocks have a high level of paleoproductivity.Low ratios of Pr/Ph and high ratios of gammacerane/C30-hopane reflect high salinity of water,strong oxygen-deficient reducing environments during deposition and favourable preservation conditions for organic matter.During the sedimentary period of source rocks in E3dL,the climate was warm and semihumid,and the mixed source was dominant in the biological source composition with more input from terrestrial higher plants,and the reducing fresh water environment is the main sedimentary environment.In general,its productivity level and preservation condition are relatively worse than the two formers',leading to lower organic content as a whole and worse organic matter types.