黄河口凹陷南部缓坡带馆陶组河流相层序特征

Characteristics of Fluvial Sedimentary Sequences of Guantao Formation in the Southern Gentle Slope Belt, Huanghekou Sag

黄河口凹陷馆陶组主要为辫状河沉积,泥岩盖层缺乏,勘探未予重视。通过岩心、测井、地震资料综合分析,认为黄河口凹陷南部斜坡带发育辫状河和曲流河两种沉积体系。利用河流相层序地层学分析方法,建立了研究区馆陶组的层序地层格架,划分出了2个三级层序(SQG2和SQG1),每个三级层序都包含一个高可容纳空间体系域和一个低可容纳空间体系域。在此基础上,总结了该区馆陶组沉积层序演化特征,在SQG2层序低可容纳空间体系域发育期,研究区为辫状河沉积,主要发育多期复合的辫状河道砂体,在SQG2层序高可容纳空间体系域发育期,研究区为曲流河沉积,主要发育孤立的点砂坝砂体和高比例的泛滥平原泥。SQG1层序演化特征与馆陶组下段类似,由于SQG1层序发育时期,可容纳空间处于较高水平,因此SQG1段砂体的粒度和砂岩百分含量比馆陶组下段整体偏小。黄河口凹陷南部缓坡带馆陶组的两套曲流河沉积可以作为良好的盖层,为油气聚集创造条件。在本次研究的指导下,研究区相继获得了一定的油气发现。

Guantao formation in Huanghekou sag is dominated by braided?river deposits and is lack of mudstone cap rocks,enough attention has not been paid to the exploration in the formation.Based on the comprehensive analysis on the data of core,logging and seismic,it is considered that the braided?river deposits and meandering river deposits are developed in the southern slope belt of Huanghekou sag.Using the sequence stratigraphy analysis method,the paper establishes a sequence stratigraphic framework for the Guantao formation in the study area,and classifies two 3?order sequences,namely SQG2 and SQG1,each of which contains a high accommodation system tract(HAST)and a low accommodation system tract(LAST).Based on which,the paper summarizes the characteristics of the sedimentary se?quence evolution of Guantao formation in the study area.The study area was dominated by braided river deposits which mainly contained multi?period composite braided river sandbodies during the development of the low accommodation system tract of SQG2;during the devel-opment of the high accommodation system tract of SQG2,the study area was dominated by meandering river deposits which mainly con?tained isolated pointbar sandbodies and a high proportion of flood plain mud.The evolution characteristics of SQG1 sequence was similar to that of the lower Guantao formation.During the development of SQG1 sequence,the accommodation maintained a high level,so the grain size and sandstone percentage of the sandbodies in SQG1 were lower than those of Guantao formation.The 2 sets of meandering river depos?its in Guantao formation of the southern gentle slope belt in Huanghekou sag can be the good cap rocks and provide good conditions for oil and gas accumulation.Guided by the study,oil and gas have been discovered successively in the study area.