| Diagenesis of reservoirs affects pore development, distribution and reservoir quality. Relevant studies on the
Middle Triassic Leikoupo Formation in central Western Sichuan Basin are still blank. In order to reveal the diagenetic
evolution characteristics of dolomite reservoirs in the study area and their influence on reservoir quality, and to provide a
theoretical basis for the exploration of carbonate oil and gas, the study on the dolomite diagenesis of Leikou Formation in
western Sichuan Basin is systematically analyzed on the basis of data analysis such as core and thin section observations,
dolomite order degree analysis, fluid inclusions and carbon-oxygen stable isotope tests. The results show that: (1) The
Leikoupo Formation in central Western Sichuan mainly develops two different types of dolomite: micritic dolomite and
micritic algal clast dolomite. The low degree of ordering and low formation temperature of the dolomite crystals indicate
that they were formed by penecontemporaneous dolomitization. The reservoir spaces mainly consist of dissolved pores
developed along algal frameworks, intergranular pores, and tectonic breccia interstices. (2) The dolomite in the study area
has mainly undergone diagenetic processes such as fracturing, dolomitization, dedolomitization, dissolution, micritization,
cementation, and surface-induced demineralization. Among them, structural fracture and dissolution play an improving
role in the physical properties of the reservoir. Deep dissolution is the fundamental factor for the development of deep
secondary pores. (3) The correlation between the development characteristics of dissolution pores and structural breccia
and structural fractures is confirmed: acidic fluids were injected along the fracture space into the remaining pore
development areas such as sandy shoal and the framework of the algal layer to form secondary dissolution pores in the late
Indosinian stage. Vertical fissures and late structural breccia were formed in the early stage of the Himalayan Movement,
and late dissolution and calcite vein filling occurred. Horizontal fractures formed in the late Himalayan period, further
improving the physical properties of the reservoir. The research has for the first time clarified the diagenetic sequence and
pore evolution model of the dolomite reservoir of the Leikoupo Formation in central Western Sichuan Basin, and proposes
a three-stage reservoir control mechanism of "structural fracture-fluid dissolution-fracture modification", providing new
geological basis for the exploration of the Leikoupo Formation |
