SEDIMENTARY FACIES AND FAVORABLE SAND BODY DISTRIBUTION OF JIUFOTANG FORMATION IN LUDONG DEPRESSION, KAILU BASIN

To study the sedimentary characteristics and distribution of favorable sand bodies in the sequence stratigraphic framework of Jiufotang Formation in Jiaolige area of Ludong depression, Kailu Basin, the paper adopts grey correlation analysis method to calculate the comprehensive evaluation factor of reservoir quality index (RQI) and predict the favorable reservoir facies belt, and defines the dynamic changes of different sedimentary systems and sedimentary facies distribution during the sedimentary evolution process of Jiufotang Formation. The strata can be divided into lowstand system tract, lake-flooding system domain and highstand system tract through the identification of sequence interface and system tract interface. Two sedimentary systems of nearshore accumulation-semi deep lake and fan delta-shore shallow lake are alternately developed in the system tract. The front facies belt is mainly developed in the fan delta during the late lowstand system tract and lake-flooding system domain periods. Eight sedimentary microfacies are identified based on the lithofacies, seismic facies characteristics and fine characterization of single well. Through the detailed characterization of sedimentary facies distribution characteristics, the reservoirs are divided into three categories, among which the reservoir formed by traction flow depositional sand bodies in fan delta front is the best, while those formed by nearshore accumulation, debris flow and torrent originated sand bodies in the front root are the worst. The results may provide a basis for further exploration and development of the study area.