Abstract:

The huge reef-bank complexes developed in the Upper Ordovician along the Tazhong Ⅰ slope-break zone feature in large areas of shoals and small size of reefs,and vertical multistage accretion and overriding of multicycle reef-bank and lateral connection as a whole.Static and dynamic data indicate low matrix porosity of the complex,suggesting a reservoir with super low permeability.The reef-bank complex also developed cavityfracture reservoirs,cavern reservoirs and cavity reservoirs.The secondary dissolution cavities and structural fractures are the most effective reservoir and flow space.The researches show that the favorable sedimentary facies belt is the foundation for the formation of reef-bank reservoirs,high-quality reservoirs mainly distribute along the reef-bank facies belt on the edge of platform,karstification and tectonism are essential for improving the poroperm characteristics of the ancient carbonate reservoirs,and the large fracture-rug systems formed by these factors contribute most to the high and stable production of oil and gas.

Key words: fracture, reservoir characteristic, karstification, reef-bank complex, Tazhong Ⅰ slope-break zone