Abstract: The fourth member of Xujiahe Formation in Jianyang Block of Tianfu Gas Field is an emerging area for increasing reserves and production of near-source tight gas in Sichuan Basin, and the study of its reservoir characteristics and main controlling factors is very important. In this study, the basic characteristics and classification of reservoirs are discussed in detail by means of casting thin slice, particle size analysis, whole rock, scanning electron microscope and high-pressure mercury intrusion, and the main controlling factors of reservoir development and evolution are systematically analyzed in many aspects. The delta-lake sedimentary system is mainly developed in Xu 4 member of Jianyang Block, and the high-quality reservoirs are mainly concentrated in the microfacies of underwater diversion channel at the delta front. The reservoir lithology is mainly lithic feldspar sandstone and feldspar lithic sandstone, among which intragranular and intergranular dissolved pores develop frequently. The porosity of the reservoir is mainly distributed between 6 and 8%, and the permeability is between 0.05 mD and 0.3 mD. Based on the comprehensive sedimentary facies belt, reservoir characteristics and fracture development degree, the classification evaluation standard of Class Ⅰ-Ⅳ tight sandstone reservoirs in the fourth member of Xu Formation is established, and the study area is dominated by Class Ⅱ fracture-pore reservoirs. The microfacies of underwater diversion channel and estuary dam lay the foundation for reservoir development, and the intragranular (intergranular) dissolved pores formed by feldspar and cuttings during hydrocarbon generation and acid drainage period are the key to the development of high-quality reservoirs, and structural fractures are an important supplement to reservoirs. The main exploration direction of tight gas is the underwater diversion channel and estuary bar sand body in the delta front with good source-reservoir configuration, developed structural faults and improved fault activity in the foreland slope zone.

Key words: Sichuan Basin, Jianyang block, Near-source tight gas, Tight sandstone, Reservoir characteristics, Reservoir classification, Main controlling factor