Abstract: The characteristics and primary controlling factors of high-quality dolomite reservoirs in the Qixia Formation in the northwestern Sichuan Basin were studied based on the diversity of their genesis and distribution. Through field studies, observation and analysis of cores and lamellae, and interpretation of well log images, the lithology and spatial characteristics of the Qixia Formation reservoir were summarized and the patterns of distribution of dolomite reservoirs in the Qixia Formation were analyzed. Finally, the main factors controlling the development of high-quality dolomite reservoirs in the Qixia Formation are discussed. It is believed that (1) the particle size in the Qixia Formation-coarse-grained dolomite and sugary dolomite-reflect a significant increase in the thickness of grain-bearing facies in the uplift near the end of the Carboniferous fully demonstrates that the paleogeomorphology before the Permian deposition controlled the distribution of beach facies in the Qixia Formation. (2) The Qixia Formation in the northwestern Sichuan Basin is a phased dolomite reservoir. The primary reservoir lithology is subhedral-euhedral-coarse grain dolomite, saccharoid-subhedral-intermediate grain dolomite, with obvious residual particle imaging, intergranular development of porosity, replacement of bright-grain limestone with dolomite, and inheritance and adjustment of intergranular pores in the original limestone. (3) The Qixia Formation in northwestern Sichuan experienced multiple hydrothermal activities in deep-buried conditions, and development of intergranular dissolution pores in medium-to-coarse-grained dolomite and dissolution pores in the dolomite crystal face. Beach-phase dolomite superimposed with buried hydrothermal activity and tectonic fracture reconstruction have resulted in large-scale distribution of high-quality dolomite reservoirs.

Key words: northwestern Sichuan, Qixia Formation, dolomite reservoir, beach facies, dissolution