Abstract: To understand the influences of sedimentary facies on tight sandstone gas reservoirs,this paper studied in-detail the sedimentary facies and their control on tight sandstone gas reservoir distribution of the Penglaizhen Formation in the central western Sichuan Depression by using outcrop,core,logging and seismic data.The Penglaizhen Formation can be stratigraphically divided into 2 long-term,4 middle-term and 29 short-term sedimentary cycles.The deposition of Penglaizhen Formation is controlled primarily by the short-axis provenance in the northwestern Longmen Mountain and secondly by the long-axis provenance in the eastern part.Alluvial fan,alluvial plain,braided river delta and lacustrine depositional systems occur successively from piedmont of Longmen Mountain to Chengdu sag.The eastern area is dominated by a fluvial depositional system.The gas-bearing sand bodies of the Penglaizhen Formation mainly occur in the western delta plain,delta front distributary channels and river mouth bars,as well as the eastern fluvial point bars and mid-channel bars in the forms of discrete sands.The potential gas-bearing traps are jointly controlled by the superposition of sand bodies and slope structural setting.

Key words: sedimentary facies, tight sand gas, Jurassic, Chengdu Sag, western Sichuan Depression