陆相断陷咸化湖盆有机质差异富集因素探讨——以东濮凹陷古近系沙三段泥页岩为例

Factors Controlling Differential Enrichment of Organic Matter in Saline Lacustrine Rift Basin:A case study of third member Shahejie Fm in Dongpu Depression

我国中、新生代陆相断陷咸化湖盆广泛发育含盐泥页岩,蕴藏着大量页岩油资源。页岩油“甜点”发育与有机质富集密切相关,但含盐泥页岩有机质差异富集主控因素研究相对较少,且存在争议。以渤海湾盆地东濮凹陷为例,针对古近系沙三段泥页岩取芯,开展总有机碳(TOC)、扫描电镜、能谱分析以及主量、微量和稀土元素分析,探讨泥页岩的有机质丰度与古气候、古盐度、沉积速率、古生产力和氧化还原条件的关系。结果表明:沙三段泥页岩的有机质富集主要受控于古生产力、古盐度和沉积速率。古生产力越大,有机质富集程度越高;随古盐度和沉积速率升高,有机质富集程度先增大后减小。氧化还原条件对有机质富集的影响不大,这与泥页岩整体发育于缺氧的还原条件有关。只有在高的古生产力、适当的古盐度和适当的沉积速率背景下,方才利于沉积有机质富集。泥页岩的有机质差异富集是非常规油气沉积学研究的重要内容之一,揭示有机质差异富集主控因素,对我国陆相页岩油勘探开发具有重要意义。

Saline shales are widely developed in the Mesozoic and Cenozoic continental saline lacustrine rift basins in China,containing abundant shale oil resources.The development of"sweet spots"in shale oil plays is closely related to the organic matter richness,but the key factors controlling differential enrichment of organic matter in saline shales are still unclear few and controversial.Taking the Dongpu Depression in the Bohai Bay Basin as an example,this study conducted the TOC,FE-SEM,energy spectrum,major,trace,and rare earth elements analyses on the Es3(Third member of the Paleogene Shahejie Fm)Shales,exploring the correlations among the organic matter richness with paleoclimate,paleo-salinity,sedimentation rate,paleo-productivity,and redox condition.Results show that the organic matter enrichment degree is jointly controlled by paleo-productivity,paleo-salinity and sedimentation rate.The greater the paleo-productivity is,the greater the organic matter enrichment degree is.With the increasing paleo-salinity and sedimentation rate,the organic matter enrichment degree increases first and then decreases.Redox conditions have little effect on the enrichment of organic matter,which is mainly related to the generally strong reduction condition of the shale cores.The combination of high paleo-productivity,proper paleo-salinity and proper sedimentation rate is most favorable for the organic matter enrichment.Differential enrichment of organic matter within shales is one of the important contents for Unconventional Petroleum Sedimentology studies.Revealing the key factors controlling differential enrichment of organic matter is of great significance to the exploration and development of lacustrine shale oil in China.