塔里木盆地下志留统柯坪塔格组沉积和层序地层特征OA北大核心CSTPCD

Objectives:The third-order sequence division of the Lower Silurian Kepingtage Formation in the Tarim Basin was different based on different research locations or areas,which restricted the understanding of the regional tectonic—sedimentary evolution and the direction of oil and gas exploration of these strata.So it is necessary to analysis the sedimentary characteristics and divide the third-order sequence of these strata again. Methods:In order to reasonably divide its third-order sequence,we have combined with all data of outcrops,published wells and seismic,existing research results,the detailed analysis of the sedimentary and sequence characteristics of the outcrop of the Kepingtage Formation in Aqia area,Keping County. Results:① The Kepingtage Formation in Aqa area is mainly a delta sedimentary system controlled by mixed hydrodynamics dominated.From bottom to top,the lower member is a sedimentary cycle from fining-up to coarsing-up,and the middle and upper members form a coarse-up sedimentary cycle as a whole.② The unconformity surfaces at the top,bottom and inside of the Kepingtage Formation can divide it into two third-order sequences.The lower member constitutes SQ1,with LST,TST and HST.The middle and upper members constitute SQ2,with only TST and HST.③ The boundary between the middle and the lower members of the Kepingtage Formation may correspond to the unconformity formed by the sea level decline during the glacial period in the Late Ordovician Hernantian.④ As the hydrodynamic conditions of different system tracts are different,the LST is dominated by river effect,while the wave and tide effect is greater than the river effect in HST.⑤ TST in SQ2 is a regional high-quality cap rock,which can form a good cap-reservoir combination with HST in SQ1.Therefore,HST of SQ1 in the western Awati sag can be the primary exploration target in this strata. Conclusions:In Aqia area,the Kepingtage Formation belongs to a delta sedimentary system formed with the mixed hydrodynamics,and it can be divided into two third-order sequences.The study has a new significance for oil and gas exploration about these strata.