湖相盆地细粒混合沉积岩形成机理及油气地质意义研究

Along with the deep exploration of unconventional hydrocarbon reservoirs, fine-grained sedimentary rocks attracted increasing attention in sedimentology. Fine-grained sedimentary rocks in lacustrine basin are mixed deposits. They are shown as uniform or clutter mixing, ordered assemble and lamina overlay by two or more mineral compositions. The mineral category and content, hybrid mode, depositional model immediately affected the characters of lithology, physical property, oil bearing and brittleness. Therefore, the studies on sedimentary characteristics and formation mechanism of fine-grained mixed sedimentary rocks are beneficial to the further exploration and development of fine-grained unconventional hydrocarbon reservoir. The second member of Kongdian formation in Cangdong depression is the promising exploration field of fine-grained unconventional hydrocarbon. Based on the study of fine-grained mixed sedimentary rocks in Cangdong depression, this project will analyze the mineral composition, classify rock types and summarize the characteristics of fine-grained mixed sedimentary rocks. Combined with sedimentary background of the basin and sedimentary characteristics of the peripheral-skeletal sand bodies, the microfacies system of fine-grained mixed sedimentary rocks will be studied, then to establish the general sedimentary models and research the formation mechanism and sedimentary dynamic mechanism of fine-grained mixed sedimentary rocks in lacustrine basin. At last, this project will study the characteristics of reservoir quality, source rocks quality and engineering quality to evaluate the oil and gas geological significance of fine-grained mixed sedimentary rocks in lacustrine basin. The work of this project will provide the scientific basis for predicting oil and gas sweet zone of fine-grained mixed sedimentary rocks.

随着页岩油气等非常规油气藏勘探程度的不断深入，细粒沉积岩逐渐成为沉积学研究的热点。湖相盆地中的细粒沉积岩以“混合”沉积为主，表现为两种或两种以上矿物成分的均匀或杂乱混合、有序排列和纹层叠置，其矿物类型及含量、混合方式、沉积模式等直接影响了细粒沉积岩的岩性、物性、含油性及脆性特征。因此，对细粒混合沉积岩沉积特征及形成机理的研究，有利于细粒非常规油气藏的深入勘探开发。沧东凹陷孔二段为细粒非常规油气前景勘探领域，本项目将以沧东凹陷孔二段为研究对象，分析细粒混和沉积岩矿物组成，划分岩石类型，总结岩石特征；结合湖盆沉积背景及周缘骨架砂体沉积特征，分析细粒混和沉积相区沉积微环境体系，建立沉积模式，探讨细粒混和沉积岩形成机理及沉积动力学机制；研究细粒混和沉积岩储层品质、烃源岩品质和工程品质特征，综合评价湖相盆地细粒混和沉积岩的油气地质意义，为细粒混和沉积岩油气“甜点”预测提供科学依据。

细粒混合沉积岩具有矿物组成复杂、岩石类型丰富、垂向演化快的特征，对其分布规律和形成机理的认识不足制约了页岩油的勘探与开发。本项目以渤海湾盆地沧东凹陷孔二段细粒混合沉积岩为研究对象，分析了岩相及岩相组合特征，明确了细粒混合沉积岩的空间展布规律，探讨了湖泊沉积环境和岩石形成机理，并根据生烃能力、储集性能以及源储配置关系等预测了细粒混合沉积岩甜点，将为沧东凹陷孔二段页岩油的勘探与开发提供依据。. 研究表明，沧东凹陷孔二段细粒混合沉积岩颜色多样、沉积构造丰富，主要由碳酸盐矿物、黏土矿物和长英质矿物组成，以三端元矿物含量50%为界将其划分为正细粒混积岩、云（灰）质细粒混积岩和长英质细粒混积岩。依据发生混合的矿物类型和混合沉积方式，研究区细粒混合沉积岩包括组分混合与组构混合2大类，进一步划分为5种混积样式。依据岩石类型、沉积构造和混积样式，识别出5种岩相类型和4种典型岩相组合。利用声波时差和密度测井数据建立识别岩性岩相的“绿模式”法，分析了Ek23SQ③时期到Ek21SQ⑨时期研究区内岩相组合的展布特征。. 孔二段沉积期沧东凹陷整体上属于潮湿-半干旱气候下的半咸水环境，不同岩相类型受陆源供应强弱以及气候变化特征双重因素控制，依此建立了4种岩相组合对应的混合沉积模式和成因环境特征。此外，通过开展有机质丰度、类型和成熟度测试，结合储集空间类型、孔隙结构特征和储集空间连通性分析，优选有利生烃岩相和有利储集岩相，综合源储配置关系等特征，预测了细粒混合沉积岩甜点类型与分布。总体来说，岩相组合2和岩相组合3有机质丰度高、生烃能力强，为有利生烃岩相组合；岩相组合1和岩相组合4储集空间发育、孔隙体积和比表面积大、储集空间连通性好，为有利储集岩相组合。基于页岩油“源-储共控”的原则，预测SQ④时期、SQ⑤时期和SQ⑨时期细粒混合沉积岩甜点发育。