歧口凹陷中部沙一下亚段异重流沉积识别特征与控制因素分析

分析陆相断陷湖盆异重流沉积的识别特征、异重流水下扇沉积体系的横向、垂向沉积序列、以及不同物源碎屑成因的异重流的沉积差异性, 从而探讨陆相断陷湖盆中异重流沉积的控制因素。以歧口凹陷沙一下异重流沉积为研究对象, 对研究区钻井岩心、测录井、地震属性以及粒度分析资料进行综合分析。结果表明, 研究区异重流具有3种典型沉积识别特征: ①两类沉积序列, 分别为下部逆粒序、上部正粒序的纺锤状二元结构沉积序列以及厚度较大且粒度特征变化不明显的均一结构沉积序列; ②粒度分析特征以递变悬浮载荷为主, 累计概率曲线类型以复杂多段式、上拱曲线式、低斜率两段式为特征; ③岩相特征为侵蚀充填沉积、广泛发育且类型多样的层理构造, 其次为陆源褐红色泥质层、褐红色泥砾以及大量的植物茎干碎片和炭质碎屑。研究区异重流沉积接受多支物源供给表现出水道化特征, 葛沽物源为最主要物源, 总体具有长距离搬运、多个朵体发育、大范围沿路沉积等特征。建立了研究区扇三角洲和辫状河三角洲物源重力流沉积模式。断陷湖盆背景下异重流沉积的控制因素为古物源、古地貌、古气候3个方面, 异重流沉积是断陷湖盆中广泛发育的沉积类型, 其中异重流水道砂岩具有良好的储集物性, 是陆相断陷湖盆油气勘探的重要方向与突破点。 

Sedimentary characteristics and controlling factors of hyperpycnal flow in the Lower Shahejie Formation of Qikou Sag,Bohai Bay Basin

This study clarified the sedimentary characteristics of hyperpycnal flow sediments, investigated the plane and vertical characteristics and the differences in hyperpycnal flow sedimentary systems from different provenances, and finally discussed the controlling factors of hyperpycnal flow in rift basins. The sedimentary characteristics of hyperpycnal flow in the Lower Shahejie Formation of the Qikou Sag, Bohai Bay Basin have been studied through the comprehensive analysis of drilling core, logging, seismic attribute, and grain data.The results show that there are three typical recognition features for the hyperpycnal flow deposits in the study area: ① The vertical sedimentary sequence is composed of a reverse grain grading in the lower part, a normal grain grading in the upper part and a relatively thick layer with no obvious change in grain size; ② The sediment is dominated by a gradual suspension. The types of cumulative probability curves include a complex multistage style, an upper arch style and a low slope two-stage style; ③ The lithofacies is characterized by erosional filling deposition and various bedding structures with the development of maroon argillaceous layers, maroon gravels, abundant plant debris and carbonaceous debris. The channelized hyperpycnal flow sediments have multiple sources. The most significant source is the Gegu source, which is characterized by a long-distance transportation path, multiple flower bodies and widespread deposits along the transportation path.Two types of sedimentary models are established in this study, and the controlling factors of hyperpycnal flow include paleogeomorphology, paleoprovenance and paleoclimate. Considering that hyperpycnal flow widely exists in rift lacustrine basins with its channel sandstone bodies being good reservoir properties, our study suggests that hyperpycnal flow is a breakthrough point for oil and gas exploration in continental rift lacustrine basins.