Abstract: Lunnan area in Tarim basin was ever been risen and denudated under the effects of early Hercynian movement in Late Devonian and late Hercynian movement in Late Permian. Its Ordovician carbonate strata underwent leaching and solution by meteoric water, and formed buried hill. Karst system very developed in Lunnan area, most of wells met strata with fissure-cavity system like Yijianfang formation and Yingshan formation. Therefore, the karstification and the tectonic movement are the key factors controlling the distribution of Ordovician reservoirs. The study shows that the reservoir bed is mainly distributed within 300 meters apart from weathering crust in vertical direction. The karstification mainly occurs in central and west part of Lunnan area, and the reservoir space is dominated by fracture/fissure, solution pore and solution cavity in lateral direction; in the east part, the reservoir space is dominated by fracture or fissure because of the effects of tectonic movements.

Key words: Tarim basin, Lunnan oil field, Ordovician, buried hill, carbonate rock