陆相湖盆富有机质页岩微相特征及对页岩油富集的指示意义——以渤海湾盆地济阳坳陷为例

Characteristics and implications of micro-lithofacies in lacustrine-basin organic-rich shale:a case study of Jiyang depression,Bohai Bay Basin

页岩油作为非常规油气资源的重要组成部分是石油地质学研究的热点之一。中国的页岩油资源大量赋存于陆相湖盆中,由于其储集、封盖、圈闭和运移等与常规油气不同,岩相对于页岩油的控制尤为显著。岩石学、全岩X衍射(XRD)、总有机碳(TOC)含量和油气显示等资料的分析表明,渤海湾盆地济阳坳陷沙河街组三段下亚段—沙河街组四段上亚段富有机质泥页岩的微相构成主要为薄透镜状晶粒灰岩微相(LF1)、纹层状泥晶灰岩微相(LF2)、厚层块状灰质泥岩微相(LF3)、块状泥岩微相(LF4)和黑色页岩微相(LF5)。其中,页岩油发育的有利微相和微相组合为黑色页岩微相(LF5)、块状泥岩微相(LF4)以及薄透镜状晶粒灰岩与黑色页岩的微相组合(LF1+LF5)。济阳坳陷有2种页岩油富集模式:(1)以块状泥岩微相(LF4)和黑色页岩微相(LF5)为主的“自生自储”模式;(2)以薄透镜状晶粒灰岩与黑色页岩微相组合(LF1+LF5)为主的“晶粒灰岩储层”模式。晶粒灰岩更有利于页岩油富集和开发生产,薄透镜状晶粒灰岩与黑色页岩的微相组合(LF1+LF5)是济阳坳陷陆相页岩油勘探开发的“甜点”岩相组合。

Shale oil is an important component of unconventional hydrocarbon resources, and is also a hot spot in research of petroleum geology. In China, shale oil resources massively occur in the continental lacustrine basin. Due to the differences between shale oil and conventional oil in reserving, sealing, trapping and migration, the lithofacies have a significant controlling effect on shale oil accumulation. This study focuses on organic-rich shale in the lower sub-member of Member 3 to upper sub-member of Member 4 of Shahejie Formation in Jiyang depression, Bohai Bay Basin. Based on the petrology, whole-rock X-ray diffraction (XRD), total organic carbon (TOC) content and direct hydrocarbon indication (DHI) of the study layers, it is indicated that the micro-lithofacies of shale layers are dominated by thin lenticle crystalline limestone micro-lithofacies (LF1), lamellar micritic limestone micro-lithofacies (LF2), thick massive lime mudstone micro-lithofacies (LF3), massive mudstone micro-lithofacies (LF4)and black shale micro-lithofacies (LF5). Among them, the favorable micro-lithofacies (or combination)for shale oil accumulation are LF5, LF4 and LF1+LF5. There are two shale oil accumulation models in Jiyang depression:one is the "self-generation and self-reservoir" model dominated by LF4 and LF5;the other is the "crystalline limestone reservoir" model dominated by LF1+LF5. The crystalline limestones are more beneficial to shale oil accumulation, development and production, and the LF1+LF5 is the "sweet spot" micro-lithofacies combination for continental shale oil exploration and development in Jiyang depression.