东濮凹陷古近系沙河街组沙三段沉积期湖岸线的变化及岩相古地理特征

东濮凹陷沙三段地层为深水相暗色泥岩与砂岩频繁互层及深水相暗色泥岩与盐膏岩频繁互层.这种砂体是东濮凹陷很重要的含油气储层。过去这种砂体往往按照静态的模式被解释为重力流成因，随着勘探的不断深入，越来越多的证据表明这些砂体中存在着牵引流和暴露地表的标志，其成因和沉积模式需要重新认识。东濮凹陷沙三段沉积时期，湖平面变化频繁，有长周期，也有短周期。根据录井、电性及岩心等资料识别出湖平面变化的5级周期,其变化频率约为1000次/Ma。根据计算，东濮凹陷沙三段沉积时期湖水最大深度为30 m。高水位沉积期,湖岸线距盆地中心较远，盆地沉积中心发育暗色泥岩夹薄层碳酸盐岩,盆地边缘发育粗碎屑岩沉积；水位下降期,边缘相砂体不断向盆地中心进积；低水位期湖岸线向盆地中心退缩了1030 km，盆地沉积中心发育盐膏岩沉积,盐膏岩的周围发育低水位三角洲、扇三角洲和滨湖滩坝相的粗碎屑岩体。正是由于湖平面的变化引起的湖岸线迁移，导致高水位沉积期和低水位期湖盆的岩相古地理面貌发生很大的变化，根据这种动态的模式来预测砂体的分布，在指导油气勘探中产生了明显的效果。

Shifting of lake shoreline and lithofacies palaeogeographic characters during sedimentary period of the Member 3 of Shahejie Formation of Paleogene in Dongpu Sag

In Dongpu Sag, the sediments of the Member 3 of shahejie Formation consisted of dark-colored mudstone of deep water facies interlayered with sandstone and salty-gypsum, and this kind of sandstone is the important oil-bearing reservoir in Dongpu Sag and its origin was explained to be deep water gravity flow sediments according to the static sedimentary model. During the process of exploration, more and more evidences are found to indicate that there are traction flow and exposure to air markers in the sandstone. So, it is needed to reunderstand its origin and sedimentary models. In Dongpu Sag, during the sedimentation of Member 3 of Shahejie Formation, the lake 1evel fluctuated frequently with long scale cycle and short scale cycle. According to the data of well log, response of resistivity and core, cycles of 5 scales were recognized, and the frequency of the fifth scale cycle is 1000 times/Ma. The minimum extent of lake level fluctuation is calculated according to the thickness of single halite bed or single gypsum bed, and the maximum water depth is 30 meters. Combining with the palaeotopography character, the reason of large transference of lake shoreline in landscape orientation has been explained. On the basis of the study, a dynamic sedimentary model is established, as it is revealed in this model, delta and beach sandbody was deposited along the shoreline and black mud with thin layer carbonate rock was deposited in the deposition center during the high stand time, and during the low stand time, the shoreline shifted about 10~30 km toward the basin center. The sand body early deposited along the shoreline was eroded and was prograded toward the sedimentation center of the basin. Because of the fluctuation and lake level and the shifting of shoreline, the paleogeograhy of highstand time and lowstand time are very different. According to this dynamic sedimentary model to predict the distribution of sand body, there will be more clear result in the petroleum exploration.