Ordovicion reef in Lunan-Bachu area of Tarim basin have been discovered recently in Middle Ordovicion Yi Jianfang Formation and Upper Ordovicion Sang Tama Formation.The reef-build-up organism are mainly composed of Calathium

Lithistida

Batostoma and Archaeoscyphia etc.The reef body

small in size and variety in type

is generally made up of reef base

reef core and reef cap.Characterized by low-porosity-low permeability or low porosity-middle permeability based on the analysis of porosity and permeability

rocks of reef reservoir are not good in general

but the porosity of reef base and reef cap is higher than that of reef core.The reservoirs

controlled by sedimentary structure and diagenesis

are mainly in types of fracture and pore-fracture.