桑塔木地区三叠系曲流河三角洲存在证据与沉积特征

Evidences and sedimentary characteristics of triassic meandering river delta in Sangtamu area

为了厘清桑塔木地区三叠系砂体成因类型,指导油气勘探,利用岩心、钻测井、分析化验及高精度三维地震资料,研究碎屑岩的粒度、结构、沉积构造、砂体的空间展布、地震反射特征等.结果表明:三叠系TⅡ油组具有粒度细、分选磨圆好、发育小型交错层理、波状层理及水平层理,呈指状产出,地震剖面上具有前积反射构型,典型相干体地层切片见曲流特征的特点,是典型的曲流河三角洲沉积;同时,研究区曲流河三角洲发育2种亚相6种微相,其中平原亚相发育天然堤、水上分流河道及河漫沼泽微相,前缘亚相发育水下分流河道、河口坝和支流间湾3种微相;区内TⅡ油组以发育北部和西南部2个主要方向的曲流河三角洲为主,其中北部三角洲规模大,平原和前缘亚相较发育,西南部三角洲以前缘亚相为主,平原亚相以分流河道沉积为主,前缘亚相主要发育分流河道和河口坝微相.该三角洲的形成与地形坡度及气候的变化密切相关.

In order to identify the origin of Triassic sandstone of Sangtamu area to direct petroleum prospecting effectively,this paper recognized it through the comprehensive analysis of cores,logging,analysis assay as well as high resolution three dimension seismic data,by the grain size,the texture,sedimentary structure,distribution characteristics of sandstone,as well as seismic reflection and strata slice characteristics.The results show that the TⅡ oil-member is meandering river delta,which has characteristics of fine grain size,well sorted and roundness,developing small-scale cross beddings and wavy bedding,showing finger shape,as well as prograding reflection architecture and plain meandering features.Based on a synthetic study of its sedimentary characteristics of Triassic TⅡ oil-member,we identified 2 subfacis and 6 microfacies in the study area,including the meandering river delta plain distributary channel,levee,flood swamp,meandering river delta front subaqueous distributary channel,mouth bar and tributary bay.The meandering river delta mainly distributed in the north and southwest of study area,the north is more huge,developing delta plain and front subfacies,while the southwest only developed delta front subfacies.The delta plain primarily developed distributary channel,and the delta front mainly developed subaqueous distributary channel and mouth bar.The formation of meandering river delta is closely related to the topographic slope and climate change.