High Resolution Sequence Framework And Sedimentary Characteristics Of Donghe Sand Member Of The HLHT Sag In Tabei Uplift

The Donghetang Formation in Halahatang Sag of Tabei uplift has always been considered as a favorable region to find lithologic-stratigraphic traps.The obviously longitudinal heterogeneity of reservoirs has been found at the top of the Donghe Sand member and based on this discovery,it provides a possibility of looking for lithologic stratigraphic traps.Based on the study above,more delicate researches for the sequence stratigraphy and sedimentary facies are urgently needed,which will be helpful to predict favorable zones eventually where lithologic-stratigraphic traps develope in the study area.The high resolution sequence stratigraphy of the Donghetang Formation,types of sedimentary facies,distribution characteristics and controlling factors of the vertical heterogeneity were studied comprehensive guided by the theory and methods of sequence stratigraphy,high resolution sequence stratigraphy,sedimentology,seismic sedimentology and petroleum geology.Based on the integrated study of core logging and seismic data,the unconformity interface between TC and TD is identified,and the Donghetang Formation is divided into a 3rd order sequence which contains a complete transgression-regression cycle structure named SQ-Ddh.Based on the study above,five transgression interfaces including the MFS are distinguished based on the sedimentary cycle recognition marks which are reflected by the particle sizes and clay content variation which are found by the drilling cores.Six high solution sequence stratigraphic units of the Donghetang Formation in the study area are recognized and five main transgression interfaces were recognized including MFS which were used to be 4th order sequence interfaces.Through comparing with this kind of high resolution sequences,local denudation at the top of the Donghe Sand member is confirmed and the distribution range of the denudation pinch-out line in the top sequence is depicted.There are three sedimentary systems including shore facies,delta facies and estuarine facies based on cores,logging and seismic data.With the integrated analysis of single well sedimentary facies,sedimentary resource,paleotopography,cross-section and seismic attributes of the target area,distribution characteristics of sedimentary facies is studied.Estuary sedimentary facies is found within the TST of SQ-Ddh,and delta front deposition is also recognised in the adjacent Donghetang area in the northwest direction in the HST besides the development of a wide range of sub-facies of near-shore,foreshore.On the basis of high-resolution sequence stratigraphy and sedimentary micro-facies analysis in the study area,the influence of the calcareous cementation development on the reservoir's physical property and the control action of high-frequency transgression interface and sedimentary micro-facies to calcareous cementation are preliminarily discussed.Combined with the previous research results and Tarim oilfield exploration achievements,the Ha15-2and ha16-1 well area of is thought to be the favorable region where lithologic-stratigraphic traps develop in the Donghe Sand member.