顺德北凹恩平组二段大型辫状河三角洲沉积特征与形成机制

    Sedimentary characteristics and formation mechanisms of large-scale braided river deltas in the second member of the Enping Formation in the Shunde North Sag

    • 摘要: 恩平组二段为顺德北凹最重要的勘探层系,但由于该区勘探起步晚,亟须加强大型储集体特征与形成机制等石油地质基本条件的研究。本文基于钻井岩性、沉积构造、粒度特征、测井曲线及三维地震等资料,开展了顺德北凹恩平组二段辫状河三角洲特征、发育条件、展布规律及发育模式的研究。研究认为,顺德北凹周缘恩平组二段发育以神狐隆起、顺德低凸起供源形成的辫状河三角洲沉积体系,明确多级宽缓的地貌奠定了大型辫状河三角洲发育的地形基础,充足的物源供给控制了大型辫状河三角洲的规模,断裂平面展布与活动性控制了辫状河三角洲注入位置与推进距离,多期的湖平面变化控制了大型辫状河三角洲的纵向演化。受北部神狐隆起和南部顺德低凸起两大物源区控制,顺德北凹形成了北部、南部及西侧3大辫状河三角洲沉积体系,整体具有短轴较长轴方向辫状河三角洲发育、北部较南部辫状河三角洲规模大,纵向上可分为3期,多继承性发育,早期较晚期规模大的特征。基于此建立了恩平组二段北部大物源区断裂聚砂、南部缓坡古沟谷聚砂、凹陷长轴断槽聚砂共3种辫状河三角洲发育模式,指出北部大物源区断裂聚砂与凹陷长轴断槽聚砂为大型辫状河三角洲的有利发育模式,明确来自北部大物源区的辫状河三角洲为顺德北凹勘探突破的最有利方向。

       

      Abstract: The second member of the Enping Formation is the most important exploration sequence in the Shunde North Sag. However, due to the late start of exploration in this area, there is an urgent need to strengthen the research on the basic petroleum geological conditions such as the formation mechanisms of large-scale reservoir bodies. Based on the data of drilling lithology, sedimentary structures, grain size distribution, loggings, and 3D seismic data, we studied the development conditions, distribution patterns, and development models of the braided river delta in the second member of the Enping Formation in the Shunde North Sag. Results show that in the second member of the Enping Formation in the Shunde North Sag, a braided river delta sedimentary system was developed, which was sourced from the Shenhu Uplift and the Shunde Low Uplift. It is clear that the multi-level wide and gentle geomorphology laid the topographic foundation for the development of large-scale braided river deltas. Sufficient provenance supply controlled the scale of large-scale braided river deltas. The planar distribution and fault activity controlled the injection position and advancing distance of the braided river deltas. The multi-stage lake level changes controlled the vertical evolution of large-scale braided river deltas. Controlled by the two major provenance areas, namely the Shenhu Uplift in the north and the Shunde Low Uplift in the south, three braided river delta sedimentary systems, namely the northern, southern and western ones, were formed in the Shunde North Sag. As a whole, the braided river deltas in the short axis direction are more developed than those in the long axis direction, and those in the north are larger than those in the south. Vertically, it can be divided into three stages with multi-inheritance development, and the scale in the early stage is larger than that in the late stage. Based on this, three development models of braided river deltas were established, namely the fault sand accumulation in the large provenance area in the north, the paleo-gully sand accumulation on the gentle slope in the south, and the fault trough sand accumulation along the long axis of the sag. The fault sand accumulation in the large provenance area in the north and the fault trough sand accumulation along the long axis of the sag are favorable for the development of large-scale braided river deltas. The braided river delta sourced from the northern large provenance area represents the most favorable direction for exploration breakthroughs in the Shunde North Sag.

       

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