准噶尔盆地腹部上二叠统-下三叠统浅水辫状河三角洲沉积特征与模式

Sedimentary characteristics and sedimentary model of the Upper Permian-Lower Triassic shallow braided river delta in the hinterland of the Junggar Basin

准噶尔盆地下组合油气资源规模巨大,是最重要的战略接替领域;腹部四大凹陷二叠系—三叠系发育规模三角洲砂体,并在其中连获油气新发现。为了揭示腹部凹陷区沉积特征、沉积模式和砂体展布规律,基于大量新钻井岩心、测录井和地球物理资料,系统开展了盆地原型、层序格架、古地貌恢复和沉积体系研究。准噶尔盆地腹部上二叠统—下三叠统浅水辫状河三角洲发育期具有大型坳陷湖盆发育背景,沉积时期地形平缓,坡度小,物源供给充足,水体极浅且频繁动荡,氧化和还原环境交替出现,且整体以氧化环境为主;浅水辫状河三角洲具有粒度较粗、低杂基含量、中等结构成熟度、较长距离搬运、强水动力淘洗、发育交错层理和平行层理等沉积特征;腹部地区上乌尔禾组—百口泉组沉积时期优势水系主要来自西北和东北方向,整体自北向南延伸,发育乌尔禾、克拉玛依及克拉美丽3大物源体系。盆内地形分带性明显,形成扇三角洲区、辫状河三角洲平原区、前缘区和湖区4个相带,由此在腹部地区形成了“大平原、小前缘”的浅水辫状河三角洲沉积格局,其中平原区和前缘区均为有利砂体发育地带。

The lower play of the Junggar Basin has huge oil and gas potential,which is the most important strategic succession field for oil and gas exploration.Large⁃scale delta sand bodies are developed in Permian and Triassic in the four sags in the hinterland,in which new discoveries of oil and gas have been made in succession.In order to reveal the sedimentary characteristics,sedimentary model,and distribution patterns of sand bodies in the hinterland,the studies on basin prototype,sequence framework,paleogeomorphic restoration and sedimentary system were systemati⁃cally carried out based on a large number of newly drilled cores,logging and geophysical data.The results show that:the development background of large depression lake basin can be identified in the development period of the Upper Permian-Lower Triassic shallow water braided river delta in the hinterland of the basin,and the study area has the characteristics of flat terrain,small slope,sufficient material supply,extremely shallow and frequently turbulent water bodies,alternating oxidation and reduction environments,and overall oxidation environment during the sedimentation period.The shallow braided river delta is characterized by coarse grain size,low impurity content,medium texture maturity,long distance transportation,strong hydrodynamic scouring,cross bedding and parallel bedding.The advan⁃tageous water system in the sedimentation period of the Upper Wuerhe and Baikouquan formations in the hinterland mainly comes from the northwest and northeast,and extends from north to south as a whole,with three provenance systems developed,namely Wuerhe provenance,Karamay provenance and Kelameily provenance.The terrain within the basin has obvious zoning characteristics,forming four facies belts namely fan delta area,braided river delta plain area,front area and lake area,thus forming a shallow water braided river delta sedimentary pattern of“large plain,small front”in the hinterland,where plain area and front area are favorable sand body development zones.