Some breakthroughs have been made in the exploration of the Middle Permian Qixia and Maokou Formations in the Sichuan Basin in recent years

indicating great prospects for gas explorationin the Middle Permian of this area.Previous studies focused on sedimentary facies and reservoirs of the Middle Permian in this area

but there are many differences in terms of the types and model of sedimentary facies of the Middle Permian Qixia and Maokou Formations.This has restricted the prediction of favorable reservoir distribution.Therefore

we carried out facies marker analysis including petrologic feature

sedimentary structure and biological fossil

based on the comprehensive study of some latest drilling and seismic data.The results show that the major sedimentary facies of the Middle Permian Qixia and Maokou Formations include platform margin

open-platform and intra-platform sag

among which the carbonate platform is dominant in the lower Qixia Formation of the Middle Permian

while rimmed platform and isolated intra-platform sag dominate the middle and upper Qixia Formation as well as in the Maokou Formation.The reservoirs of the study area are mainly marginal-platform and intra-platform shoals

concentrating in highstand system tracts.The marginal-platform shoal reservoirs mainly occur in areas including Ya'an-Mianzhu and Jiange-Guangyuan during the Sq1-HST period

and Ya'an-Mianzhu-Guangyuan area during the Sq2-HST period;the intra-platform shoal reservoirs are mainly distributed in the Gaoshiti-Moxi block in the central Sichuan Basin during the Sq1-HST and Sq2-HST periods

and Weiyuan-Zigong area during the Sq2-HST period.The intra-platform shoal reservoirs in Gaishiti-Moxi block during the Sq2-HST period are distributed in the form of strips due to the joint influences of paleokarst and tectonic hydrothermal fluids.The marginal-platform and intra-platform shoals are widely distributed in the Middle Permian of Sichuan Basin

and have bright prospects for hydrocarbon exploration.