Reservoir sedimentary characteristics of XII sand group of the 3rd member of Qingshankou formation in the Daqingzijing oilfield

The Qingshankou formation of lower Cretaceous in Songliao Basin is one of the most important Mesozoic basin oil layers,the Ⅻ sand group of the Qingshankou formation developed lots of sand bodies of various types.In order to figure out the sedimentary microfacies of the Ⅻ sand group of the 3rd member of Qingshankou formation,based on the description and observation of the core,combined with the regional geology,seismic,logging,grain size,and lithological characters,the investigation into the sedimentary microfacies of the Ⅻ sand group of the 3rd member of Qingshankou formation have been carried out in detail.The results show that the target area develops the delta sedimentary system under the background of the water back.During the sedimentary period of Ⅻ sand group,the lake basin recession accelerated,the sedimentary sources of water system was not stable,and mainly came from the Southwest and South of Tongyu-Baokang drainage.The delta body migrated massively,finally inherited the characteristic of the delta sedimentary system of the 2nd member of Qingshankou formation.The studied area mainly developed the delta plain and frontdelta,but the prodelta developed slightly.We mainly identified the distributary channel,underwater distributary channel,channel mouth bar,front bar,and offshore bar.It is obvious that the reservoir property is significantly affected by sedimentation,the reservoir property of the distributary channel and channel mouth bar in the research area are the best.