Keywords: 
• Northeast Sichuan Basin /
• Feixianguan Formation /
• Platform marginal shoal /
• Depositional evolution /
• Favorable reservoir zone

Abstract: [Objective]The Lower Triassic Feixianguan Formation in Sichuan basin develops thick oolitic beach reservoirs, which is the key layer of current oil and gas exploration. As the reserve strategic replacement field of Sichuan Basin, the sedimentary system, reservoir characteristics and favorable zone distribution of Feixianguan Formation in Tieshanpo and Qilibei areas are not clear, which restricts the deployment of oil and gas exploration in this area. [Methods]Based on the comprehensive analysis of core, rock slice, logging and seismic data, the sedimentary facies types, evolution rules and favorable reservoir zones of the Lower Triassic Feixianguan Formation in Tieshanpo and Qilibei areas were studied. [Results]The Feixianguan Formation in the study area develops a rimmed platform model, which can be subdivided into five sedimentary facies:restricted platform, open platform, platform edge, slope and basin. The platform margin is the favorable facies belt for the development of oolitic beach. The development of oolitic shoals in the area has obvious aggradation-lateral accretion characteristics, which are mostly superimposed in 2 to 3 periods vertically, and are distributed in ssq2 to ssq4 periods, with the largest scale in ssq2 period. Horizontally, the beach body is unstable and has a tendency to migrate into the basin; The reservoir rock types are mainly (residual) oolitic limestone, (residual) oolitic dolomite and powder crystal-fine crystal dolomite. [Conclusions]The platform margin oolitic beach is a favorable microfacies for reservoir development in Feixianguan Formation, and the porosity and permeability conditions are good. The area of wells Po5-Poxi1-Po2-Po1 in the Tieshanpo area is a favorable reservoir development zone, and the area of wells Qilibei1-Qibei102 in Qilibei area is a potential favorable reservoir development zone.The spatial and temporal distribution and migration law of beach bodies in different areas of the fourth-order sequence framework and the prediction results of favorable reservoir zones can provide a basis for deepening the exploration and development of oolitic beach reservoirs in this area.