高频湖平面变化下薄砂层高精度层序地层特征及沉积演化——以温宿凸起周缘-英买力隆起地区库姆格列木群底砂岩段为例

High-resolution sequence stratigraphy characteristics and sedimentary facies evolution of thin sands under highfrequency lake level change:A case study of lower sand member of Paleogene Kumugeliemu Group in margin of Wensu Uplift-Yingmaili Uplift area

塔里木盆地塔北隆起西部温宿凸起周缘-英买力隆起地区库姆格列木群底砂岩段是近年来岩性油气藏勘探的热点层位,且玉东1井区已获得了规模的油气产量,但底砂岩段高精度层序地层特征、沉积微相类型及其时空演化规律有待落实。综合利用岩心、钻井、测井和地震资料,识别可以等时追踪对比的标志层、层序界面和湖泛面,构建底砂岩段的高精度层序地层格架,分析各高频层序单元的沉积微相类型和特征,并揭示沉积相的时空演化规律。库姆格列木群底砂岩段为三级层序ESQ1的上升半旋回,可分为4个准层序组,从下到上依次为4砂组、3砂组、2砂组和1砂组。库姆格列木群底砂岩段沉积时期为湖水不断变深、湖盆逐渐扩大的“水进砂退”的沉积背景,发育扇三角洲、辫状河三角洲和湖泊3种沉积相类型,其中4砂组至3砂组沉积时期,为低可容纳空间的低位域体系,物源供给充足,且湖平面上升缓慢,温宿凸起物源区和英买力隆起物源区均发育较大规模的三角洲,英买力隆起物源区还发育规模较大的滨浅湖砂坝。2砂组至1砂组沉积时期,为高可容纳空间的湖侵域体系,湖水迅速变深,温宿凸起物源区沉积物供给迅速减少,扇三角洲迅速向盆地边缘退积迁移,湖水将早期砂体淘洗再沉积形成小型砂坝。英买力隆起物源区三角洲逐渐萎缩,滨浅湖砂坝规模显著变小。

The lower sand member of Paleogene Kumugeliemu Group in the margin of Wensu Uplift-Yingmaili Uplift area in Tarim Basin has become the focus for lithologic reservoir exploration in recent years,and the massive oil and gas has been produced from Well Yudong1 Block.However,the high-resolution sequence stratigraphy characteristics,sedimentary microfacies types,and temporal-spatial evolution laws were not yet clear.Based on core,drilling,logging and 3D seismic data,the markers,sequence interfaces,and flooding surfaces which can be isochronally tracked and compared were identi⁃fied.A high-resolution sequence stratigraphy framework was constructed,under the constraint of which the types and char⁃acteristics of sedimentary microfacies of each high-frequency sequence unit were analyzed and the temporal-spatial evolution laws of sedimentary microfacies were revealed.The results show that the lower sand member of Paleogene Kumuge⁃liemu Group is the ascending half cycle of the third-order sequence ESQ1 and can be divided into four parasequence sets,namely sand member 4,sand member 3,sand member 2,and sand member 1 from bottom to top.The sedimentary period of the lower sand member of Paleogene Kumugeliemu Group is characterized by gradually deeper lake water and bigger lake basin,thus resulting in“water progradation and sand retrogradation”.Three types of sedimentary facies such as fan delta,braided river delta,and lake are developed here,in which the sediment period from sand member 4 to sand member 3 fea⁃tures the lowstand system tract with small accommodation space,adequate source supply,and slowly rising lake level.Large deltas are developed in the source areas of Wensu Uplift and Yingmaili Uplift and large near lakeshore sand bars are developed in Yingmaili Uplift source area.The sediment period from sand member 2 to sand member1 is featured by the transgressive system tract with large accommodation space and fast deeper lake water.Swiftly,the source area supply of Wensu Uplift decreases;the fan delta retrogrades towards the basin edge;the early developed sand is washed by the water and redeposited to be small sand bars.The delta in Yingmaili Uplift source area shrinks gradually and the near lakeshore sand bars apparently shrink.