SEDIMENTARY MICROFACIES AND SAND-BODY DISTRIBUTION MODEL OF THE XISHANYAO FORMATION IN THE SHIXI AREA OF JUNGGAR BASIN

Core description and laboratory data indicate that the sandstones of the Xishanyao Formation in the Shixi area are very immature. Charcoal and carbonized plant stems as well as parallel and trough like cross beddings are common in sand and gravel deposits. Through the multidisciplinary study of regional geological data, well logs and core description data, we discussed the sedimentary systems of the Xishanyao Formation in the Shixi area. The sequence suggests a facies of meandering river delta, consisting of three sub-facies and 10 microfacies including the deltaic plain, distributary channel, crevasse splay, flood plain, deltaic swamp, subaqueous distributary channel, tributary bay, mouth bar, distal bar, subwater natural levee, and prodelta. The sand-body distribution pattern of the Xishanyao Formation was discussed on the basis of sedimentary facies. Data indicate that the sequence is dominated by the sandstones of subaqueous distributary channel, mouth bar, distributary channel, and deltaic swamp. Logging responses of various sedimentary microfacies were studied in this paper. The results show that the distribution pattern of sand-bodies are obviously controlled by sedimentary facies.