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Objective The beach facies dolomite reservoir in the Middle Permian Qixia Formation， central Sichuan Basin， has significant potential for oil and gas exploration， but relatively little systematic study has been reported on its diagenetic sequence and pore evolution. Methods The petrology and pore genesis of the Qixia Formation were investigated by core observation， thin section analysis， cathodoluminescence examination and image recognition techniques， to delineate diagenetic variations and pore evolution in the different lithologies. Results In the Gaoshiti area， four types of rock are identified in the Qixia Formation： micrite limestone， micrite grain limestone， sparite grain limestone， and residual grain dolostone. Four types of reservoir space are observed： intergranular dissolved pores， intragranular dissolved pores， fractures and vugs. Each rock type has undergone distinctive diagenesis： the type and intensity of dissolution vary in the different lithologies. The two kinds of granular limestone are mainly dissolved by meteoric water， and the residual granular dolomite is more strongly dissolved by meteoric water. On this basis， dolomitization and burial period dissolution occur. Recrystallization is more pronounced in the residual grain dolomite， whereas compaction and pressure dissolution is more evident in micrite grain limestone. The key diagenesis and stages influencing pore development vary between the different rock types： the pores in the two types of granular limestone are mainly formed by quasi-syngenetic dissolution， then partially destroyed by compaction and cementation during the burial stage. The dissolution and dolomitization in the parasyngenetic stage result in the formation and preservation of the pores in the residual granular dolomites； dissolution and tectonic fracture at the burial stage are beneficial supplements， but cementation during the shallow burial stage destroys the pores. Conclusions The varied diagenesis has caused different pore evolution， forming four lithologies with a decreasing extent of pore development： residual grain dolostone （plane porosity： 2.10%）， sparite grain limestone （plane porosity： 1.24%）， micrite grain limestone （plane porosity： 0.41%） and micrite limestone （compact）.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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