川东二叠纪生物礁的再认识

RESTUDIES ON PERMIAN REEFS IN EASTERN SICHUAN,CHINA

通过川东 8口二叠纪长兴期钻井岩芯剖面的详细研究 ,铁山 5井、天东 10井代表典型的礁相剖面 ;板东 4井、双 15井既有礁相沉积 ,且有棘屑滩沉积 ;卧 117井、黄龙 1井以及云安 14井基本上由碳酸盐台地沉积组成 ;池 2 4井出现两种类型的礁相 :海绵骨架礁和海绵障积礁。川东礁相剖面中的白云岩以海水与淡水混合作用而成的白云石化为主导因素 ,但它们在深埋阶段以后 ,又遭受后期白云石化的叠加 ,因此表现出许多深埋白云石化的地化特征。白云岩的原始沉积既可能是礁骨架岩 ,也可能是棘屑滩 ,甚至是碳酸盐台地沉积。因此在寻找礁型白云岩储层时 。

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.