基于中期旋回洪泛面的河流相地层等时划分

在高分辨率层序地层学理论的指导下，以中期旋回的洪泛面为基准，根据不同时期河道砂体顶面的高程差异划分地层单元，可以实现河流相地层的等时划分与对比。以渤海Q油田北区明化镇组下段N₂m²油组为例，基于砂体发育频率和高程差异构建了一套河流相地层等时划分方法：首先对地震相、测井相、砂岩发育特征等进行综合分析，识别后期河道的下切位置，"回填"被侵蚀破坏的部分，恢复中期旋回末期的原始洪泛泥岩界面，将其作为等时地层划分的基准；然后根据砂体发育的频率特征以及砂体顶面与中期旋回洪泛面的高程关系，构建等时界面识别曲线，刻画泥岩的集中发育位置，识别短期或超短期旋回的等时界面，实现地层的等时划分。实例分析表明，该方法能够有效识别不同地层单元之间的界面位置，将N₂m²油组划分为6个等时单元，不同时期河道的沉积特征符合中期基准面上升半旋回内的河道沉积演化规律。

Isochronous Stratigraphic Division of Fluvial Facies Based on Mid Term Cycle Flood Surface

This paper focuses on the study of fluvial facies isochronous stratigraphic division based on a medium cycle flood surface. Under the guidance of the high resolution sequence stratigraphy theory, based on the flood surface of a middle period cycle, the stratigraphic division of river facies were divided and contrasted according to the elevation difference on the top of channel sand bodies in different periods. Taking the N₂m² oil group in the lower section of the Minghuazhen Formation in the north part of the Bohai Q oilfield as an example, the authors established a set of methods for fluvial facies isochronous stratigraphic division based on the sand body development frequency and elevation difference. According to the comprehensive analysis of seismic facies, logging facies,and sandstone development characteristics, the downcut position of the later channel was identified. As a basis of isochronous stratigraphic division, the original flooding mudstone interface at the end of the medium-term cycle was restored after backfilling the part that had been eroded. According to the frequency characteristics of sand body development, and elevation relationship between a sand body top surface and a medium cycle flood surface, the equal time interface recognition curves were constructed. These curves are used to characterize the concentrated development positon of mudstone and to identify the isochronous interfaces of short or ultra short cycles. Based on the above work, the isochronous stratigraphic division is realized. A case analysis shows that this method can idendify the interface positions between different stratigraphic elements effectively in dividing the N₂m² oil group into six isochronous units, and the sedimentary characteristics of river courses in six periods conform to the sedimentary evolution pattern of the middle term base level rising semi-cycle.