济阳坳陷博兴洼陷西部沙三段层序地层

ANALYSIS OF SEQUENCE STRATIGRAPHY OF THE 3RDMEMBER OF SHAHEJIE FORMATION IN THE BOXING SUB-DEPRESSION,JIYANG DEPRESSION

选取以基准面为参照面的高分辨率层序地层学的理论与分析技术,对博兴洼陷西部沙三段开展层序地层分析工作。在博兴洼陷沙三段识别出5个层序界面和4个较大规模的洪泛面,由此将研究层段划分为4个长期基准面旋回(相当于3级层序),并通过长期旋回内部次级转换面的识别,细分出8个中期旋回(大致相当于4级层序)。通过对比建立了研究区的高分辨率层序地层格架,并分析了各层序的地层发育特征。以层序格架为基础,探讨了研究区各层序的沉积演化特征,建立了辫状三角洲—浊积扇层序发育模式,认为研究区辫状三角洲和浊积扇均具有加积作用特点;斜坡区为辫状三角洲发育区,而洼陷区为浊积扇发育区;中期基准面旋回下降期辫状三角洲发育,上升期浊积扇发育;浊积扇体的发育规模与湖泛规模相关。综合分析认为,浊积扇是形成岩性圈闭的主要储集砂体类型,其发育的有利层位是MSC8、MSC7、MSC6、MSC5旋回的上升半旋回,岩性圈闭发育的有利区是博兴南部斜坡坡折带之下的洼陷区。

The authors carried out the analysis of sequence stratigraphy of the 3rd member of Shahejie Formation in western Boxing sub-depression with high-resolution sequence stratigraphy with base level as the reference surface. Five sequence boundaries and four flooding surfaces are recognized in the 3rd member of Shahejie Formation. According to these surfaces,the member is divided into four long-term base level cy cles. Moreover,there are eight medium-scale base level cycles through recognizing inner turnaround surfaces of the long-term base level cycles. High-resolution sequence stratigraphic framework is constructed through correlations among wells and seismic profiles. Characters and depositional evolutions of each se quence are analyzed in the sequence framework. Based on the above analysis, sequence stratigraphic models for braided river delta to turbidite fan are constructed. Braided river deltas and turbidite fans have the upgrading characters; the former are distributed in slope areas and the latter are generally distributed in depression areas. Braided river deltas are concentrated in the falling hemi-cycles of base level and turbidite fans in the rising hemi-cycles. The scales of turbidite fans are relative to lake flooding surfaces. We draw a conclusion that turbidite fan is the main type of reservoir to lithologic traps. The favorite members to lithologic traps are the rising hemi-cycles of MSC5,MSC6,MSC7 and MSC8;and the favorite areas to lithologic traps are the depressions at the break of the south slope of Boxing sub-depression.