Abstract: The fourth member of Xujiahe Formation (Xu 4 member) in Jianyang block of Tianfu Gas Field is an emerging field for increasing
reserves of continental facies near-source tight gas in Sichuan Basin, and the study of its reservoir characteristics and main controlling factors is very crucial. Using casting thin section, grain size, bulk rock, scanning electron microscope and high-pressure mercury injection data, the basic characteristics and classification of reservoirs are discussed in detail, and the main controlling factors for reservoir development and evolution are systematically analyzed in multiple aspects. The delta–lake sedimentary system was mainly developed in Xu 4 member in Jianyang block, and the high-quality reservoirs were mainly concentrated in delta front underwater distributary channel microfacies. The reservoir lithology is mainly composed of lithic feldspar sandstone and feldspar lithic sandstone, with intragranular and intergranular dissolution pores commonly observed. The reservoir porosity generally ranges from 6% to 8%, and the permeability is in the range of 0.05–0.3 mD. Based on the comprehensive study of sedimentary facies zone, reservoir characteristics and fracture development degree, the classification evaluation standard for Class Ⅰ– Ⅳ tight sandstone reservoirs in Xu 4 member is established, and Class Ⅱ fractured-porosity type reservoir is dominant in the study area. The delta front underwater distributary channel and mouth bar microfacies laid the foundation for reservoir development. The intragranular (intergranular) dissolution pores of feldspar and lithics formed by hydrocarbon generation and acid drainage are the key to the development of high-quality reservoirs, and tectonic fractures are important supplement to reservoir space. In the foreland slope zone, source rock–reservoir configuration is superior, and tectonic faults are well developed, in which delta front underwater distributary channel and mouth bar sand bodies improved by late fault activity are the main orientation for tight gas exploration.

Key words: Sichuan Basin, Jianyang block, near-source tight gas, tight sandstone, reservoir characteristics, reservoir classification, main controlling factor