Study on Sedimentary Microfacies of No.3 Sand Group of Gaotaizi Reservoir in West Slope in Northern Songliao Basin

The analysis result of abundant cores,logging,and well logging data reveals lacustrine facies and delta facies are main sedimentary facies types of No.3 sand group of Gaotaizi reservoir in north and west slope of Songliao Basin.Lacustrine facies are composed of shore-shallow lacustrine subfacies,which are subdivided into 3 sedimentary mircorfacies: sandy beach-bars,mixed beaches and muddy beaches.Delta facies are mainly composed of delta frontal edge esuarine bars and distal end bars.During its sediment,No.3 sand bed formation of Gaotaizi reservoir forms five delta lobe bodies,under the influence of Qiqihaer,north,west and southwest material sources.The deltas formed by Qiqihaer,north and southwest material sources are larger than that formed by west material source.The deltas developed into frontal edge subfacies,which are composed of estuarine bars and distal end bars microfacies.No.3 sand bed formation of Gaotaizi reservoir developes shore-shallow lacustrine sandy beach bars microfacies in the area of Fu 62 well-Fu13 well,Du 408 well-Du 405 well and Du 431 well-Ta 4 well.The distribution of zonary shore-shallow lacustine sandy beach-bars along the maximum lacustine bank line in the area of Fu 62 well-Fu 13 well is bigger.In other areas,shore-shallow lacustrine mixing beaches microfacies mainly developed with rich muddy sediments.Near Jiang 36 well and Lai 54 well shore-shallow lacustrine muddy beaches microfacies developed.Sandstone-mudstone rate is sensitive to sedimentary microfacies.In the area where estuarine bars and sandy beack-bars micorfacies developed,sandstone-mudstone rate is generally above 0.4.!In the area where distal end bars micorfacies developed,sandstone-mudstone rate is nearly 0.3.In the area where shore-shallow lacustrine mixing beaches micorfacies developed,sandstone-mudstone rate is nearly 0.2.In the area where shore-shallow lacustrine muddy beaches micorfacies developed,sandstone-mudstone rate is generally under 0.1.