冀中坳陷束鹿凹陷湖相富碳酸盐矿物细粒沉积岩成因机制及其对储层孔隙的影响和制约

Currently, fine-grained sedimentary rock is a hot issue in international sedimentology field. Lacustrine carbonate-rich fine-grained rocks are wildly developed in the Paleogene in Eastern Basins of China. Nevertheless, the origin mechanism of the rocks and the factors affecting the reservoir porosity are still unclear. This study focuses on lacustrine carbonate-rich fine-grained rocks in the Shulu Sag, southern of the Jizhong Depression. Based on petrology, sedimentology, geochemistry, and high-precision instruments, the lithofacies and sedimentary environments of the fine-grained rock and the origins of major components of the fine-grained rock, such as calcite, dolomite, quartz, organic matter, will be investigated in detail. The origin mechanisms of different types of the fine-grained rocks will be analyzed synthetically. In addition, the types, size, distribution, and abundance of various pores in the reservoir will be quantitatively analyzed. By comparing the differences of porosity characteristics from different origins and different types of fine-grained rocks, the forming mechanism and main control factors of the fine-grained reservoir properties will be identified. The influence degree of each factor on the reservoir porosity will be discussed. The control mode of genesis and diagenesis of lacustrine carbonate-rich fine-grained rock on its porosity will be established. This study will be helpful to improve the theory of origin mechanism of lacustrine fine-grained rock and guide the unconventional oil and gas exploration and development in the Eastern China. Thus, this project has important scientific and practical significance.

细粒沉积岩是当前国际沉积学研究的热点，我国东部盆地古近系广泛的发育湖相富碳酸盐矿物细粒沉积岩，但对其成因机制以及储层孔隙的制约因素等尚不明确。本项目以冀中坳陷南部束鹿凹陷为研究对象，综合岩石学、沉积学、地球化学等，并运用高精度测试手段，对该区各种类型的富碳酸盐矿物细粒沉积岩的岩相、沉积环境、及细粒岩中方解石、白云石、石英、有机质等主要组分的成因进行详细研究，综合分析该区不同类型湖相富碳酸盐矿物细粒岩的成因机制。通过对该储层中孔隙类型、各类孔隙的大小、分布、丰度等进行定量表征，对比分析不同成因、不同类型细粒岩的孔隙特征差异，确立研究区细粒岩储层形成机理及主控因素，查明细粒岩各组分及成熟度等因素对细粒岩储层孔隙的影响及制约程度，建立该区湖相富碳酸盐矿物细粒岩成因-成岩作用对储层孔隙的控制模式。该研究有助于完善湖相细粒岩成因机制及指导我国东部湖相非常规油气勘探开发，具有重要的理论意义及现实价值。

细粒沉积岩是当前国际沉积学研究的热点。冀中坳陷西南部束鹿凹陷沙三下亚段发育以泥灰岩为主的富含碳酸盐矿物的岩层，具有较好的油气显示，为华北油田重要的致密油勘探领域。但目前对该细粒岩的成因机制以及储层孔隙的制约因素尚不明确。项目综合岩石学、沉积学、地球化学等，对该富碳酸盐矿物细粒沉积岩成因机制及其对储层孔隙的影响进行研究。.研究区岩石所含矿物主要有方解石、白云石、粘土矿物、石英长石、黄铁矿，其中方解石为最主要矿物。研究认为该区方解石有四种成因，1)机械成因；2)生物化学成因；3)后期成岩形成；4)生物碎屑。根据成分、颗粒大小、及构造等，将研究区岩相分为8类：颗粒支撑陆源砾岩、杂基支撑陆源砾岩、混源砾岩、碳酸盐岩岩屑砂岩、碳酸盐岩岩屑粉砂岩、纹层状泥灰岩、块状泥灰岩、灰质泥岩。其中纹层状泥灰岩发育两种类型，一种具有规则的纹层，为季节性变化所形成的季节性纹层，沉积于深湖、缺氧还原环境；另一种具有不规则的纹层，纹层内部发育粒序构造，为泥质浊流成因。块状泥灰岩为浊积云沉淀而成，形成于相对动荡的环境。. 束鹿凹陷沙三下富有机质泥灰岩厚度大，分布面积广，有机质丰度高，类型好（主要为II型和I型干酪根），处于热成熟阶段，有很大的原始生烃潜力。油源对比结果指示束鹿凹陷沙三下原油源自沙三下富有机质泥灰岩，表明束鹿凹陷沙三下岩层是一种特殊的自生自储、近源成藏、连续聚集的非常规油气藏。.该致密储层的主要发育微米-纳米级孔隙。储集空间类型包括：砾内孔缝、贴砾缝、粒间孔隙、晶间孔隙、粒内孔隙、溶蚀孔隙、有机质孔隙、裂缝等。其中砾内孔缝，贴砾缝，溶蚀孔隙，白云石晶间孔，有机质孔隙及裂缝是较优质的储集空间类型。储集性能主要受有机相、岩相、及裂缝发育的控制。有机质不仅控制着生烃能力，也决定着有机质孔隙、溶蚀孔隙、异常压力缝等储集空间的发育。在不同的岩相中，颗粒支撑陆源砾岩及高有机质纹层状泥灰岩物性最好。