SEDIMENTARY FACIES OF UPPER TRIASSIC XUJIAHE FORMATION IN SOUTHWEST SICHUAN BASIN

Sequence stratigraphic division and correlation and study of favorable depositional facies are of important significances for petroleum exploration and development in the southwestern Sichuan Basin. Based on comprehensive study of core, seismic and logging data, the Upper Triassic Xujiahe Formation in the study area is divided into 4 third-order sequences, 12 system tracts, 4 types of sedimentary facies including bay, lake, braided river and normal delta, and over 20 sedimentary microfacies. Favorable reservoir sandbodies include delta (underwater) distributary channels and mouth bars. The distribution of sandbodies is characterized by both inheritance and differentiation, and they have migrated along with the change of major sources of sediments at different periods. The development of sandbodies is mainly controlled by structures, source of sediment and paleogeomorphology.