庙西南凸起馆陶组浅水辫状河三角洲沉积特征及砂体演化

Sedimentary Characteristics and Sand Body Evolution of Shallow Braided River Delta of Guantao Formation in Miaoxi'nan Uplift,Bohai Sea Area

基于大量已有钻井、地球物理、分析化验数据,渤海海域庙西南凸起馆陶组被证实具有稳定的构造环境、平缓的古地形、半干旱—干旱气候条件、充足的物源供给、古水深较浅的背景,因而具备形成浅水辫状河三角洲的条件。受制于特殊的气候环境,形成"大平原,小前缘"的沉积特征,水体面积较小,受河流作用改造为主,平原亚相砂体以具有双段式粒度概率曲线和强水动力沉积构造的分支河道为特征;干旱气候条件下不稳定的水体导致代表氧化环境的紫红色泥岩与代表弱还原环境的灰绿色、杂色泥岩呈交互沉积。依据气候变化、相对湖平面变化和物源供给等方面的耦合关系将研究区馆陶组浅水辫状河三角洲砂体形态分为孤立叠置式、多边叠置式及切叠连片式三种,分别对应馆陶组早中晚三个时期。砂体演化分析证实古地形、气候变化及相对湖平面变化是影响本区砂体样式的关键因素,馆陶组中部多边式砂体储层连通性好、平面分布广而顶部砂体平面分布广储层厚,为本区下一步勘探的重点。

Based on a large number of drilling,geophysical and analytical data,the Guantao Formation of Miaoxi＇nan Uplift in the Bohai sea area was confirmed to have stable tectonic environments with gentle ancient topography,semiarid-arid climate,sufficient source supply,and shallow ancient water depth. All these conditions were suitable for the formation of a shallow braided river delta. For its special climate environment,the great plains and small front of sedimentary characteristics formed,the water area was small and dominated by river actions. The sand bodies of plain subfacies were characterized by branching channels with double section probability curves of grain size and strong power of sedimentary structures. In addition,under arid climatic conditions,unstable water bodies caused purple red mudstone on behalf of the oxidizing environment to interact with grey green and variegated mudstone on behalf of the weak reducing environment. On the basis of climate change,the relatively lake level change and provenance supply,the shallow braided river delta sand body of the Guantao Formation in the study area can be divided into isolated type,multilateral type and fold type,corresponding to each period of the Guantao Formation. Sand body evolution analysis confirmed that the ancient terrain,climate change and relative lake level variation were the key to influence sand body styles. The multilateral type of reservoir sand body of the middle period of Guantao Formation had good connectivity and flat wide distribution. The top part of the sand body reservoir with plane distribution and thickness could be a key target for the next exploration in this area.