准噶尔盆地中央坳陷西部风城组岩相古地理及油气勘探

Lithofacies Paleogeography and Petroleum Exploration of Fengcheng Formation in Western Central Depression of Junggar Basin

为评估准噶尔盆地中央坳陷西部风城组油气勘探前景,利用微量元素、岩心、岩石薄片、古地貌、测井相、地震相等的综合分析,开展了研究区风城组岩性组合和沉积相研究。结果表明,研究区风城组是在前陆构造背景、干旱—半干旱气候、水体盐度与水深呈周期性变化的环境下的扇三角洲—碱湖沉积。从坳陷边缘至中心,依次形成盆缘扇三角洲碎屑岩类、斜坡外前缘白云质岩类、斜坡高地火山岩类、低隆带白云质灰质滩坝混积岩类和中心湖盆碱层岩类。根据沉积特征,建立了风城组扇三角洲—碱湖沉积及演化模式。结合沉积相、岩相和油气勘探现状,研究区风城组可划分为盆缘超削带常规油气区、斜坡外前缘致密油气区、湖盆页岩油气区、低凸起周缘常规油气区和高地火山岩常规油气区,7000 m以浅的勘探有利面积达1.2×10^(4)km^(2),油气储量达十亿吨级,展现了研究区风城组全油气系统内巨大的勘探潜力。

In order to evaluate the petroleum exploration prospects of the Fengcheng formation in the western Central depression of the Junggar basin,the lithology assemblage and sedimentary facies of the Fengcheng formation were studied by means of analyzing the trace element,core,rock thin section,paleomorphology,logging facies and seismic facies of the formation.The results show that the Fengcheng formation in the study area is fan delta-alkaline lake deposition which formed in an arid-semiarid climate,foreland tectonic setting and geological environment with periodic changes in water salinity and water depth.From the edge to the center of the Central depression,basinmarginal fandelta clastic rocks,outerslope front dolomites,slope-highland volcanic rocks,lowuplift dolomitic calcareous beachbar peperites,and the central lakebasin alkali rocks are found in sequence.According to the sedimentary characteristics,an evolution model for the fan delta-alkali lake deposition was established for the Fengcheng formation.Based on the sedimentary facies,lithofacies and petroleum exploration status,the Fengcheng formation in the study area can be divided into 5 areas such as conventional hydrocarbon area in basinmargin ultradenudation belt,tight hydrocarbon area in outerslope front,shale oil/gas area in lake basin,conventional hydrocarbon area in lowuplift dolomitic calcareous beachbar and conventional hydrocarbon area in highland volcanic rocks.The favorable exploration area with the depth less than 7000 m reaches 1.2×10^(4)km^(2),with hydrocarbon reserves of more than one billion tons,which demonstrates huge exploration potential of the total petroleum system of the Fengcheng formation in the study area.