Abstract: The discovery of Ordovician carbonate reservoir in Tahe oilfield foreshowed that Tarim basin has bright prospect of searching for giant oil-gas pools. This paper comprehensively studied various data such as drilling, geology, lab analysis and experiment or testing, and pointed out that the basic petroleum geologic conditions for forming Tahe oilfield include: source rocks around three sides indicates abundant hydrocarbon supply; pores, caves and fissures are good places of reservoir network; cap rocks superposition each other shows good sealing and screened conditions; the trapping condition is good; faulting and reservoir are channels for oil-gas migration; and reconstruction and damage in late period are smaller, conservative conditions are better, etc.

Key words: Tarim basin, Tahe oilfield, Ordovician, carbonate rock, oil-gas reservoir formation, geologic characteristics