The first submember of the fifth member of the Lower Ordovician Majiagou Formation in Xingkian

Shanxi Province is located at the top of a paleo-weathered crust and consists mainly of micrite and small amount of micritic dolomite. The intercalations in it contain some amountes of argillaceous rocks. The reservoir spaces are pores

caves and fractures. The primary POres are dominantly intercrystal pores; the secondary pores include intercrystal pores

solution pores and caves

bird’s eye pores

intergtavel pores; the fractures consist of structural fratures

diagenetic fractures

karst fractures and suture fractures. It is suggested that the reservoir should belong to low Permeable solution fracture-cave reservoir. The fundamental factor to effect the reservoir property is karstification.