垦利A油田沙三上段近源辫状河三角洲沉积特征

Sedimentary characteristics of near-source braided river delta of the upper third member of Shahejie Formation in Kenli A oilfield

为了搞清渤海湾盆地莱州湾凹陷古近系沙三上段沉积特征及展布规律,应用岩心、粒度、薄片统计、录井、地震等资料,总结层序格架下的沉积相类型和展布特征。结果表明:垦利A油田发育近源辫状河三角洲沉积体系,识别出辫状河三角洲平原、辫状河三角洲前缘和前辫状河三角洲3种亚相,并进一步划分出辫状河道、冲积平原、水下分流河道、水下分流河道间、河口坝及席状砂等6种沉积微相;应用层序地层学,将沙三上段划分为1套三级层序,低水位体系域(LST)以水下分流河道厚层砂岩为主,水进体系域(TST)和高水位体系域(HST)以薄层砂岩为主。不同体系域砂岩厚度及展布规模,受控于湖平面升降及沉积物供给速率。该认识可为断陷湖盆斜坡带的砂岩储层评价提供依据。

In order to reveal the sedimentary characteristics and distribution regularity of the upper third member of Paleogene Shahejie Formation in Laizhou Bay Sag,Bohai Bay Basin,the sedimentary facies types and distribution characteristics under sequence framework were summarized by using core,grain size,casting thin section,mud logging and seismic data.The results show that a typical near-source braided river delta sedimentary system developed in Kenli A oilfield.Three kinds of subfacies were recognized,including braided river delta plain,braided river delta front and pro-braided river delta,which can be further divided into the following six sedimentary microfacies:braided channel,alluvial plain,underwater distributary channel,underwater distributary interchannel,mouth bar and sheet sand.By using sequence stratigraphy,the upper member of Sha 3 was divided into a set of third-order sequence.The lowstand systems tract(LST)was dominated by thick sandstone in underwater distributary channel,while the transgressive systems tract(TST)and highstand systems tract(HST)were dominated by thin sandstone.Sandstone thickness and distribution scale in different systems tracts were controlled by lake level fluctuation and sediment supply rate.This rule can provide a reference for the evaluation of sandstone reservoir in the gentle-slope zone of faulted lacustrine basin.