Sedimentary facies and sedimentary model for the Chang 6₂ oil measures of the Triassic Yanchang Formation in the Qilicun Oil Field, Ordos Basin

Sedimentary facies and sedimentary model are constructed according to well logs and section examination of the Chang-6₂ oil measures of the Triassic Yanchang Formation in the Qilicun Oil Field, Ordos Basin. The delta front subfacies deposits predominate in the target beds in the study area, and has the "blanket" structure instead of the three-layer structure of topsets, foresets and bottom sets indicated by the Gilbert-type delta model. Sedimentary microfacies consists of the subaqueous distributary channel and interdistributary bay microfacies in the delta front subfacies. The controlling factors include tectonic evolution, palaeoclimates, lake-level changes and sediment supply systems. During the deposition of the Chang-6₂ oil measures of the Triassic Yanchang Formation, the broad channels facilitated the wide spreading of water-carried fine-grained sediments and progradation toward the center of the basin, and resulted in the formation of the "blanket" structure composed of the sandstone-mudstone couplets in the subaqueous distributary channel facies.