The Shaximiao Formation of Middle Jurassic in the southwestern Sichuan Basin is advantageous in hydrocarbon sources and hydrocarbon migration conditions, but no significant breakthrough has been achieved in natural gas exploration here for many years. In order to define the high-quality reservoirs and favorable exploration areas of Shaximiao Formation in the southwestern Sichuan Basin and guide the natural gas exploration deployment in the following step, this paper systematically analyzes the provenance characteristics, distribution of sedimentary facies zones, reservoir rock types, reservoir performance, and diagenesis effect on reservoirs in the Shaximiao Formation of this area. And based on this, the formation conditions and controlling factors of high-quality reservoirs of Shaximiao Formation tight sandstone gas are clarified, and the favorable distribution areas of Shaximiao Formation reservoirs are defined. And the following research results are obtained. First, the reservoir rock types of Shaximiao Formation in this area are primarily feldspathic sandstone and lithic feldspathic sandstone and secondarily lithic sandstone and feldspathic lithic sandstone, and their sedimentation is controlled by double provenances with lithic sandstones from the Longmen Mountain on the west and feldspathic sandstones from Micang-Daba Mountain on the northeast. Second, the reservoir performance of feldspathic sandstones is much better than that of lithic sandstones. Feldspathic sandstones are mainly vertically distributed in the first and second sub-members of the second Member of Shaximiao Formation and laterally the most developed in the eastern area. Third, the high-quality reservoirs in this area are obviously controlled by sedimentation, and the fine-medium grained feldspathic sandstones deposited in the mouth bar and underwater distributary channel are the best in physical properties. Fourth, compaction and cementation are the main factors resulting in reservoir densification and porosity reduction in the Shaximiao Formation;chlorite cementation has a certain protective effect on primary pores; and dissolution is the main factor of porosity increase. In conclusion, the feldspathic sandstone development areas of delta plain channel, delta front underwater distributary channel and mouth bar facies in the Shaximiao Formation of the southwestern Sichuan Basin are favorable distribution areas of high-quality reservoirs, and the area to the east of Xiongpo fault is an important direction of tight sandstone gas exploration in the following step. © 2022 Natural Gas Industry Journal Agency. All rights reserved.
