Sedimentary System and Sand Bodies Distribution of the 2nd Member of Xujiahe Formation in Xinchang Area, Western Sichuan Depression, China

The Xujiahe Formation of Late Triassic in the Western Sichuan Depression contains abundant gas reservoirs. Influenced by the thrust tectonic movement of foreland basin, the fluvial-delta sedimentary system supplied by multiple provenances formed the Xu2 Formation of the Xinchang area. We used detailed description of drilling wells and cores to define the sequence stratigraphic framework and sand body types. We used stratal slices through the seismic volume to map the evolution of the sedimentary system and the sand body distribution. The results show that the Xu2 Formation exhibits a complete long-term base-level cycle, and there are six sand body deposit types: distributary channel, inter-channel, subaqueous distributary channel, inter-distributary bay, mouth bar and sheet sand. Stratal slices through the seismic volume at different levels map the spatial variation of sand and mudstone, which we use to construct a sedimentary filling evolution model. This model indicates that during the time of deposition of the Lower Sub-member the main provenance supply came from the NW direction, resulting in the sand bodies mainly deposited in the west. During the time of depositon of the Central Sub-member, sediment supply was large and came from both the NW and NE directions, resulting in large, laterally extensive, thick sands. During the time of deposition of the Upper Sub-member, sediment supply was from the NE direction, with the sand bodies more developed in the east. The flow direction of the channels indicate that they migrated from northwest to northeast. There are differences in channel energy, sedimentary characteristics and reservoir physical properties in the three Sub-members, which cause differences in natural gas productivity of Xu2 Formation. We believe that detailed mapping the spatial distribution of sedimentary systems can provide critical guidance to not only explore, but also to develop in high-quality oil and gas reservoirs like Xu2 Foramtion.