Abstract:

Through the study of eight well cores from the Upper Permian reefs of Changxing stage in Eastern Sichuan,rocks from Tieshan 5 Well and Tiandong 10 well represent typical sponge reefs;rocks from Bandong 4 Well and Shuanglongchang 15 Well have not only the deposits of reef facies,but also crinoidal or echinoderm banks;rocks from Wolonghe 117 Well,Huanglongchang 1 Well and Yun'anchang 14 Well are mainly composed of carbonate platform deposits;rocks from Dachigan 24 Well consist of two types of reef facies:sponge framework reefs and sponge baffling reefs.Dolomites in the Permian reefs were formed of saline water mixed with fresh water during subaerial exposure of reefs above the sea level,then suffered late dolomitization during deeper burial stage,so they have evident geochemical characteristics of late dolomitization.The original deposits of these dolomites are of framework;not only they could be transformed by reef rocks,but also by those deposits of echinoderm banks,even common carbonate platform depostis.So in finding dolomite reservoirs of reef types,one should pay attention to find dolomite reservoirs formed of bank deposits as well as carbonate platform deposits.

Key words: reefs, Permian, Eastern Sichuan, restudy