石钱滩凹陷二叠系平地泉组层序沉积特征及石油地质意义

Sequence sedimentary characteristics and petroleum geological significance of Permian Pingdiquan Formation in Shiqiantan Sag

二叠系平地泉组为准噶尔盆地东部隆起区的重要勘探层系,隆起区西侧的帐北断褶带已在该层系发现石油地质储量丰富的火烧山油田,而东侧的石钱滩凹陷仅见到油气显示,下一步有利勘探方向不明确。通过系统分析地震、钻井、测井以及露头等资料,划分平地泉组层序地层单元,明确层序地层格架内沉积特征,建立层序沉积充填模式,分析石油地质特征。研究结果表明:石钱滩凹陷平地泉组自下而上划分为2个三级层序,层序1发育低位域、湖侵域和高位域,层序2发育低位域和湖侵域,高位域缺失。层序1沉积时期,石钱滩凹陷南北两侧分别发育三角洲、扇三角洲沉积,湖侵域发育半深湖-深湖亚相暗色泥页岩,为一套较好的烃源岩。层序2沉积时期,石钱滩凹陷自北向南发育扇三角洲、滨浅湖沉积。层序1湖侵域扇三角洲前缘、灰坪与高位域扇三角洲前缘、三角洲前缘、灰坪紧邻烃源岩,为研究区最有利的沉积相带,其中高位域三角洲前缘前积砂体是寻找岩性油气藏的有利勘探方向。

The Permian Pingdiquan Formation is an important exploration stratum in the eastern uplift area of Junggar Ba⁃sin.On the west side of the uplift area,Huoshaoshan Oilfield with abundant petroleum geological reserves has been found in Zhangbei fault-fold belt,while in Shiqiantan Sag on the east side,only oil and gas shows are observed,with an unclear future direction for favorable exploration.Through systematic analysis of seismic survey,outcrops,as well as drilling and logging data,the sequence stratigraphic units of Pingdiquan Formation were divided,and the sedimentary characteristics within the sequence stratigraphic framework were clarified.In addition,a sequence sedimentary filling model was construct⁃ed.Accordingly,the petroleum geological characteristics in Shiqiantan Sag were analyzed.The results indicate that Pingdi⁃quan Formation in Shiqiantan Sag is divided into two third-order sequences from bottom to top.Sequence1 developed the lowstand system tract,the transgressive system tract and the highstand system tract,while Sequence 2 developed the low⁃stand system tract and the transgressive system tract,without the highstand system tract.During the sedimentary period of Sequence1,deltas and fan deltas developed in the north and south of Shiqiantan Sag,and the dark shale of semi-deep deep lacustrine facies developed in the transgressive system tract,becoming a set of good source rocks.In the sedimentary period of Sequence 2,fan deltas and shore-shallow lacustrine sediment developed in Shiqiantan Sag from north to south.In Sequence 1,the fan delta front and grey flat in the transgressive system tract and the fan delta front,delta front,and grey flat in the highstand system tract are adjacent to source rocks,which are the most favorable sedimentary facies belts in the study area.The progradational sandbody at the delta front of the highstand system tract represents a favorable exploration direction for lithologic reservoirs.