Abstract:

In order to understand the reservoir distribution and therefore to promote exploration, carbonate reservoir characteristics and diagenetic features of the Middle Ordovician Yijianfang Formation in Shunnan area and its influence on reservoir formation were studied based on the core and casting thin section observation and cathodo?luminescence spectroscope analysis coupled with core?measured porosity and permeability data. The results show that the carbonate reservoir of Yijanfang Formation in the study area is mainly composed of grain limestone, microcry?stalline limestone and algal bindstone. The main reservoir spaces are dissolved pores and fractures, which formed two types of reservoirs: fractured reservoir and fractured?cavity reservoir. The porosity of the reservoir ranges from 0.20% to 3.90% with an average value of 1.52%, and the permeability ranges from 0.003 mD to 5.84 mD with an average value of 0.62 mD. The reservoir is dominated by type Ⅲ with poor physical properties. The carbonate rocks underwent complex diagenesis including cementation, compaction/pressure dissolution, corrosion （karstification） and fracturing, of which cementation （including filling of dissolved pores by crystals） has strongly damaged the reservoir while corrosion （karstification） and fracturing were major mechanisms of reservoir formation in the Yijianfang carbonate rocks.

Key words: shale gas, controlling factors for enrichment, Dongyuemiao member, Lower Jurassic, northern Sichuan Basin