The Middle and Lower Ordovician fractured-vuggy reservoirs in the Tahe oilfield experienced multi-stage karstification caused by multi-stage tectonic events from the Middle Caledonian to the Early Hercynian.Based on integration of geological

geophysical and geochemical data

we discuss the development characteristics and main controlling factors of multi-stage karstification of the Ordovician carbonates in the Tahe oilfield.Four main periods of karstification are identified as follows:the 1

st

Phase

2

nd

Phase and 3

rd

Phase of the Middle Caledonian and the Early Hercynian.The origin

evolution and transformation history of the karst reservoirs are also discussed in this paper.According to this study

the major karstification periods are the Early Hercynian

the 1

st

Phase and the 2

nd

Phase of the Middle Caledonian

of which the Early Hercynian is the most important period.The main controlling factors of kastification are paleostructures

karst topography and geological conditions of paleo-drainage-system.