| The diagenesis of the eyeball-shaped limestone traditionally interpreted as source rock has been discussed controversially. Based on field outcrops observation, thin sections identification and physical property analysis, the petrology and reservoir property of the eyeball-shaped limestone of the Middle Permian Maokou Formation are studied in East Sichuan Basin, South China, and the formation mechanism is also discussed. The macro-and micro-scopic characteristics of “eyeball” and “eyelid” are quite different. The porosity and permeability of “eyelid” are relatively good. The reservoir space of “eyelid” is mainly composed of various secondary dissolution pores. In particular, positive correlation between porosity and permeability is found within the “eyelid”, as such, this type of composition may incorporate into a conventional porous reservoir with low-porosity and low-permeability. In general, this eyeball-shaped limestone, extensively found in the whole Sichuan Basin, can be served as a relatively tight limestone reservoir for future hydrocarbon exploration. Combined the macro- and micro-features of eyeball-shaped limestone with previous research results, this study suggests that the formation of eyeball-shaped limestone reservoir is closely related to its diagenetic process. The stratified fabric differences formed in the early diagenesis stage lay a material foundation for the later exposed karstification. Moreover, the karstification after deposition is the key to the formation of reservoir. |
