湖平面频繁变化环境下的扇三角洲沉积——以黄骅坳陷枣园油田孔一段沉积为例

研究湖平面频繁变化的环境下形成的扇三角洲的特点 ,阐述了其沉积微相、相带展布和砂体分布方面的特征 ,为该区储层的预测提供了指导模型 .认为枣园油田 (黄骅坳陷 )孔一段枣 、枣 油组发育时期 ,水体不稳定 ,湖平面升降频繁 ,无固定湖岸线 .因此 ,在这种环境下形成的扇三角洲特征缺乏完整的垂向层序 ,水下沉积与水上沉积垂向上频繁叠置 ,形成多层楼式的垂向层序 ,表现为红色碎屑岩与薄层暗色泥岩频繁互层 .由于沉积物以氧化色为主 ,其特征类似冲积扇 .但该环境下沉积的砂体分布模式与冲积扇环境的砂体的分布模式有很大的差别 .红色泥夹的砂岩是席状 ,暗色泥岩所夹砂岩是指状 ,与湖岸垂直 .在平面上 ,由于湖水的周期性淹没和湖浪改造形成沿岸分布的席状砂体 .在垂向上 ,由于湖平面的频繁变化 ,使该区缺少稳定的沉积环境 ,因此砂体相对较薄 .最后建立了该区扇三角洲洪水期沉积模式和枯水期沉积模式 .洪水期和枯水期的交替发育 ,导致在同一剖面上席状砂体和透镜状 (树枝状 )砂体的交替出现

Fan-delta Sedimentation Formed Under the Environment of Lake Level Frequently Varying ——Taking the First Member of Kongdian Formation, Huanghua Depression as an Example

The characteristics of the fan delta sedimentation formed under the environment of frequent lake level variation are studied, and the sedimentary models of this kind of fan-delta are established. The microfacies and the sandbody distribution of the sedimentation are discussed. The models can be used for predicting the distribution of reservoir. By studying the lithology, color, grain size, sedimentary structure and vertical sequence of the first member of Kongdian Formation, Zaoyuan oilfield of Huanghua Depression, it is held that during the sedimentation of para-sequence set 4, para-sequence set 5 of the member, the water body is not stable, the lake level frequently changes and there is no fixed shoreline. So a complete vertical sequence can not be found in the fan delta sedimentation, and the deposits under water and on land are interbeded each other. A multi story style vertical sequence is developed, and it is made of red clastic rock and black shale with thin layers. Because the sedimentation is mainly red, its character is somewhat similar to fluvial fan. In fact there is a great difference between their sandbody distribution patterns. The sandbody in red mud is sheeted, and the sandbody in black mud is finger shaped. Because of the cyclic flooding of lake water and the reform of lake wave, the sheeted sandbody is formed along the lakeshore. In vertical direction, there is no stable sedimentary environment because of the frequent lake level variation. So the layers of sandbody are very thin. Two kinds of fan delta sedimentary models are established in lower water stage and overflow stage. During the lower water stage, distributary channels are developed, the sandbody formed is dendritic, and its lateral connectivity is poor. During the overflow stage, fan-delta front sheeted sandbody is developed and its connectivity is very good. Because of the alternation of overflow water and lower water stages, the sheeted sandbody and dendritic sandbody appear alternatively.