前陆盆地系统中隆后盆地沉积特征——以准噶尔盆地腹部侏罗系三工河组为例

Sedimentary characteristics of post⁃uplift basins in foreland basin system:a case study of Jurassic Sangonghe Formation in hinterland of Junggar Basin

前陆盆地油气资源丰富,但主要集中在前渊带,随着隆后盆地油气勘探取得突破,该类盆地逐渐成为研究热点。准噶尔盆地腹部属于隆后盆地,该区侏罗系三工河组是重要的油气产层,但是目前对于其沉积相的类型存在较大争议。随着勘探的深入推进和各种地质资料的不断丰富,三工河组的沉积相类型及演化逐渐变得清晰。为明确前陆盆地系统中隆后盆地沉积相类型、分布及与前渊带沉积特征的差异性,在扎实的野外地质剖面、岩心、测井、地震和分析测试资料分析的基础上,详细剖析了三工河组的沉积相类型、展布特征及其控制因素。准噶尔盆地腹部隆后盆地三工河组沉积相类型包括辫状河三角洲相、湖底扇相和湖泊相等。其中,辫状河三角洲相进一步划分为平原和前缘亚相,主要分布在石西和莫北地区;湖底扇相主要分布在盆1井西凹陷中,发育鲍马序列,多见“A”、“B”段,其物源来自研究区东部的辫状河三角洲。三工河组沉积期,研究区存在3个物源,而非前人认为的西北部和东北部2个物源。稳定重矿物等资料分析表明,W36湖底扇受到东北部物源影响,而W46湖底扇受到东南物源影响。前陆盆地前渊带沉积物粒度较粗,沉积相类型简单,且以构造油气藏为主;而隆后盆地沉积物粒度较细,沉积相类型多,且以构造—岩性、岩性油气藏为主。

Foreland basins are rich in oil and gas resources,with most being concentrated in the foredeep zone.However,as breakthroughs in oil and gas exploration in post-uplift basins have been made,these types of basins gradually become a research hotspot.The hinterland of the Junggar Basin is a post-uplift basin,and the Jurassic Sangonghe Formation is an important oil and gas-bearing layer in this area.However,there is still a significant debate about the types of sedimentary facies in this formation.With the progress of exploration and the continuous enrichment of geological data,the types and evolution of the sedimentary facies in the Sangonghe Formation have gradually become clearer.To clarify the sedimentary facies types,distribution,and the differences from the foredeep zone in the post-uplift basins of the foreland basin system,the study analyzed geological profiles,cores,well logging,seismic data,and analytical test results.It provided a detailed analysis of the sedimentary facies types,distribu-tion characteristics,and controlling factors of the Sangonghe Formation.The sedimentary facies types of the Sangonghe Formation include braided river delta facies,sublacustrine fan facies,and lacustrine facies.The braided river delta facies are further subdivided into the plain and front subfacies,which are mainly distributed in the Shixi and Mobei areas.The sublacustrine fan facies are mainly distributed in the west sag of well 1 in the basin,characterized by Bouma sequences,with“A”and“B”segments being mostly common.The sediment source for these fans came from the braided river delta in the eastern part of the study area.During the sedimentary period of the Sangonghe Formation,there were three sources in the study area,instead of only two sources from the northwest and northeast as previously believed.Stable heavy mineral analysis showed that the W36 sublacustrine fan was affected by the northeastern sediment source,while the W46 sublacustrine fan was affected by the south-eastern source.Sediments in the foredeep zone of the foreland basin were coarse,with simple sedimentary facies types and structural oil and gas reservoirs as the primary trap types.However,sediments in the post-uplift basin had finer grain sizes,with more varied sedimentary facies types,and were dominated by tectonic-lithologic and lithologic oil and gas reservoirs.