东营凹陷沙三段下亚段细粒沉积岩岩相特征及其分布模式

Lithofacies characteristics and distribution model of fine-grained sedimentary rock in the lower E_(s_3) member,Dongying sag

综合运用岩心观察、薄片鉴定、X衍射和扫描电镜等分析方法,对东营凹陷沙三段下亚段细粒沉积岩矿物组成、沉积构造和纹层类型及成因进行精细刻画,在此基础上建立细粒沉积岩岩相划分方案,并以樊页1井沙三段下亚段为例分析其岩相垂向演化特征。东营凹陷沙三段下亚段细粒沉积岩具有矿物组成复杂多变、受底流微弱改造作用频繁及纹层类型丰富的特点。参考矿物组成和沉积构造,研究区发育11种岩相类型,其中平直纹层粘土岩相、夹层灰岩相、平直纹层灰岩相、不平直纹层灰岩相、平直纹层混合岩相、不平直纹层混合岩相和块状混合岩相是最为发育的7种岩相类型,不同岩相发育环境差异性明显。细粒沉积岩岩相分布模式受古水深和古气候综合控制,在气候干冷、深水还原环境下主要发育平直纹层粘土岩相;气候由干冷向暖湿转变时形成夹层灰岩相;在气候半暖湿的广阔深湖环境下发育平直纹层灰岩相;在气候最为暖湿时期,底流发育,形成不平直纹层灰岩相;随着水深减小,水体分层不稳定,加之气候逐渐干冷,形成平直纹层混合岩相,若底流发育,则形成不平直纹层混合岩相;在半氧化—半还原的浅湖环境下发育块状混合岩相。

Combining core description,thin sections analysis,whole-rock X-ray diffraction and scanning electron microscopy technologies,the characteristics of mineral composition of fine-grained sedimentary rocks,sedimentary structure and laminations in the lower E_(s_3) member in the Dongying sag were described in detail,by which lithofacies of fine-grained rocks were classified and their vertical evolution characteristics were analyzed using a case from the lower E_(s_3) member drilled by Well FY1. The results show that the fine-grained rocks in the lower E_(s_3) member is characterized by complex and variable mineral composition,frequent and weak bottom current reworking and abundant laminations. Based on the mineral composition and sedimentary structure,there are eleven types of lithofacies in the study area,and seven of them are mainly developed,which are parallel-laminated clay stone,interbedded calcareous limestone,parallel-laminated limestone,nonparallel-laminated limestone,parallel-laminated mixed sedimentary rock,nonparallel-laminated mixed sedimentary rockand massive mixed sedimentary rock. Their development environment are different obviously. The distribution of fine sedimentary facies is controlled by paleo-water depth and paleoclimate. The parallel-laminated clay stone are developed mainly in deep water in dry and cold reducing environment. Interbedded limestone develops when the paleoclimate changes from dry and cold to warm and wet. Parallel-laminated limestone develops in wide and deep water when the paleoclimate is semi-warm and wet. Nonparallel-laminated limestone develops when the paleoclimate becomes the warmest and wettest and the bottom current develops. Parallel-laminated mixed sedimentary rock develops when the water becomes shallower with unstable water delimitation and the paleoclimate becomes drier and colder. And the nonparallel-laminated mixed sedimentary rock will develop if there are bottom current. The massive mixed sedimentary rock develops in semi oxidation and reduction environment.