11 / 2021-05-30 16:29:55

Sedimentary characteristics and model of deep-seated glutenite under the condition of high-frequency base-level cycle（高频基准面旋回条件下深层砂砾岩扇体沉积特征及沉积模式）

岩相 砂砾岩 基准面旋回 盐家地区 东营凹陷

摘要 深层油气已成为国内外油气勘探的焦点，进一步加强深层区域沉积特征及储层展布规律研究是油气高效勘探的关键。基于岩心观察、FMI成像测井资料、钻测录井资料、地震资料及微量元素分析等，指出东营凹陷北部陡坡带盐家地区沙四下亚段沉积期以强蒸发干热环境为主，水体相对较浅，主要发育近岸水下扇和湖底扇沉积。通过对岩性、粒度及层理构造等精细剖析，共识别出9大类岩相，4大类岩相组合类型，18种组合特征。并指出这些岩相及组合类型多受控于基准面旋回变化，且在短期-超短期旋回顶底界面尤为发育。在基准面下降半旋回（A/S减小）阶段，以颗粒支撑中-粗砾岩相、颗粒支撑细砾岩相和颗粒支撑含砾砂岩相为主，砂体厚度大、粒度粗且多期扇体相互切割叠置，平面上呈连片分布；在基准面上升半旋回（A/S增大）阶段，可见杂基支撑中-细砾岩相、含砾中-细砂岩相及泥质粉砂岩相，且多与泥岩隔层相间发育，砂体在空间上多呈孤立式或离散式。分析表明阵发性洪水造成的物源供给量差异、古冲沟形态特征（宽深比，地层坡度）及湖平面变化是区域超短期基准面旋回变化下扇体发育及空间展布的主控因素。结合岩相及其组合关系特征分析，在基准面上升时期共识别出2种砂砾岩沉积模式即高能洪水进积式和低能/间歇洪水退积式。高能洪水进积式沉积过程中扇体多成帚状分布，搬运距离较远，单期扇体平均厚度约8m，多发育于古坡度为30°～43°区域；低能/间歇洪水退积式沉积过程中扇体多呈朵状分布，搬运距离相对较近，在其前端易发生滑塌形成湖底扇沉积，单期扇体平均厚度约6.5m，多发育于古坡度为22°～38°区域。明确不同沉积模式下扇体发育特征及展布对区域优质储层分布及成岩演化差异分析，进而对油气的高效勘探具有重要意义。

关键词  岩相  砂砾岩  基准面旋回  盐家地区  东营凹陷

第一作者简介 茆书巍，男，博士，助理研究员，主要从事沉积、储层地质学及油藏精细描述等方面的研究工作。E-mail：maow100@163.com



Abstract Deep-seated oil and gas have become the focus of hydrocarbon exploration at home and abroad. To further strengthen the research on the sedimentary characteristics and reservoir distribution are the key to hydrocarbon efficient exploration. Based on core observation, FMI imaging logging data, drilling and logging data, seismic data and trace element analysis, indicating that the paleoenvironment was characterized by strong evaporation and dry-hot environment. The water was relatively shallow, and the nearshore subaqueous fan and sublacustrine fan deposition developed during the deposition period of the lower section of the fourth member of Shahejie Formation (E₂S₄²) in Yanjia area of the steep slope belt in Dongying Sag. Based on the analyses of lithology, grain size and bedding structure, 9 kinds of lithofacies are identified, which are further classified into 4 types of lithofacies combination and 18 kinds of combination characteristics. Research results proved that these lithofacies and combinations type are controlled by base level cycle changes, and developed well in the top-bottom interface of the short-term and super-short-term sedimentary cycle. In the sedimentary semi-cycle descending (A/S decreasing) stage, the lithofacies are mainly composed of medium-coarse glutenite facies, fine conglomerate facies, and pebbled sandstone facies supported by grains, which are characterized by the thick layer, coarse in size, and multistage fan bodies with cutting and superimposed on each other, showing the continuous distribution on the plane. While in the sedimentary semi-cycle (A/S increasing) rising stage, the medium-fine glutenite facies, medium-fine pebbled sandstone facies and argillaceous siltstone lithofacies, which are characterized by the interbedded development with mudstone, and dominated by the isolated or discreted distribution in space. Further analysis shows that the difference in provenance supply caused by paroxysmal floods and the morphological characteristics of ancient gullies（wide/depth ratio, paleoslope） are the main controlling factors to the variation of regional ultra-short-term base level cycle, and have important controlling effects on the vertical thickness and transverse distribution range of the fan sandbodies. Meanwhile, two types of sedimentary models are identified, named high energy flood progradation model and low energy/interval flood retrogradation model. In the process of high energy flood progradation, the fan body was mainly distributed in broom shape and transported at a long distance. And the average thickness of the single fan is about 8.5m, developed in the paleoslope of 30°～43° area. While, in the process of low energy/interval retrogradation, the fan body was distributed in shape of lobes, which is transported at a relatively short distance, and is prone to collapse and from sublacustrine fan at the front. The average thickness of the single fan is about 6.5m, and mostly developed in the region with a paleoslope of 22°～33°. It is of great significance to clarify the development characteristics and distribution of fan body under different sedimentary modes for regional high-quality reservoir distribution and diagenetic evolution difference analysis, and then for efficient oil and gas exploration.

Key words   lithofacies, glutenite, base level cycle, Yanjia area, Dongying Sag

About the first author   Mao Shu-wei, male, research assistant, is mainly engaged in research on sedimentology, reservoir geology and hydrocarbon reservoir characterization.  E-mail: maow100@163.com.