雅布赖盆地小湖次凹新河组下段层序及沉积相特征

目前雅布赖盆地小湖次凹中侏罗统新河组下段是玉门油田的主力勘探层位,其中YT6井已取得工业油流,显示出良好的勘探前景,而在层序格架下明确同期次砂体展布,将有利于油气的进一步勘探开发。基于岩心、测井、录井及地震资料的分析,依据经典层序地层学理论,对小湖次凹中侏罗统新河组下段的层序特征、沉积相类型、沉积演化规律及平面展布进行了系统研究,进而讨论了有利沉积相带的展布。研究表明,新河组下段具有完整的三级层序;主要发育扇三角洲相、辫状河三角洲相、湖泊相3种沉积相类型;次凹沉积相带发育具有南北分异、隆凹成带的特征,其中小湖次凹南部陡坡带发育扇三角洲前缘亚相,北部及西北部缓坡带发育辫状河三角洲前缘亚相,次凹中心则主要发育湖泊相;从低位期到高位期,不同时期的沉积相展布各异,总体表现出水体由浅变深,再变浅,沉积范围逐渐扩大,扇三角洲和辫状河三角洲先进积、后退积、再进积的特点;经分析认为分布于YT6井西北部新河组下段的高位域水下分流河道微相是最有利的储油相带。 

Characteristics of Sequence Stratigraphy and Sedimentary Facies in the Lower Xinhe Formation of Xiaohu Sub-sag,Yabulai Basin

The Lower Xinhe Formation of Xiaohu sub-sag,Yabulai Basin is the key exploration horizon in Yumen Oilfield.Commercial oil flows found in well YT6,show a good exploration prospect.So,under the sequence framework,well understanding the distribution of contemporaneous sand bodies is favorable to the further exploration and exploitation.This paper aims to employ the classic sequence stratigraphy,to elaborately analyze the sequence characteristics,sedimentary facies types,and sediment evolution and distribution,and discusses the distribution of favorable sedimentary reservoir,based on the data of drilling cores,loggings and seismic data.The results show that the Lower Xinhe Formation develops a complete third-order sequence.Fan delta,braided river delta and lacustrine facies are developed in the Lower Xinhe Formation.The palaeogeography of the Lower Xinhe Formation is characterized by a clear difference between the southern part and its counterpart of the basin.Fan delta front is located along the south steep fault belt and braided river-delta front is developed in the northern and northwestern gentle slope,with lacustrine sediments in the central lake.From the period of lowstand system tract to highstand system tract,sedimentary characteristics and the sedimentary facies distribution are both correspondingly different in different stages.Overall,the changes of the depth of water from shallow to deep,and then to shallow cause the sedimentary area gradually to enlarge,and fan delta,braided river delta first to progradate,then retrogradate,and finally progradate.The analysis indicates that the distributary channels of highstand system tract in the northwest of YT6 well as favorable reservoir are the future exploration targets in the study area.