Sedimentary characteristics and lithofacies paleogeography of the Cambrian in Sichuan basin,Southwest China

Cambrian in Sichuan basin developed thick black shale,varies carbonate and clastic rock,which deposited in different sedimentary environment.Sichuan basin in the upper Yangtze platform contained a record of environment during the Cambrian.Detail facies analyses of Cambrian enable us to discuss the sedimentary environment and palaeogeographic setting.Sedimentation commenced in the Early Cambrian with the deposition of shelf facies(Qiongzhusi Formation and Canglangpu Formation).At this stage,thick shale and clastic rock deposited in Sichuan basin.At the end of the Early Cambrian,a carbonate platform developed in upper Yangtze platform,and Sichuan basin was located in restricted platform(Longwangmiao Formation).In the Middle Cambrian,tidal flat and restricted platform developed in Sichuan basin(Douposi Formation),because of continuous regression.During the Late Cambrian,Sichuan basin was located in carbonate platform again(Xixiangchi Formation).There are three types of sedimentary system in the Cambrian of Sichuan basin:clastic sedimentary system,clastics-carbonate mixed sedimentary system and carbonate sedimentary system.Vertically,the basin shows the evolutionary character of clastic-carbonate sedimentary systems.The three sedimentary systems correspond to three“transgression-regression”cycles of the Cambrian.The transgression in the initial period of the Early Cambrian led to the formation of clastic sedimentary system in the Qiongzhusi Formation of Lower Cambrian.The transgression in the later period of the Early Cambrian led to the formation of clasticcarbonate mixed sedimentary system in the Middle-Lower Cambrian.The transgression in the initial period of the Late Cambrian led to the formation of carbonate sedimentary system in the Xixiangchi Formation of Upper Cambrian.With the end of Late Sinian continental rifting ended,Sichuan basin entered a stable evolutionary stage of the craton basin,while the paleo-land developed in the north and southwest.In Qiongzhusi-Canglangpu period,the basin developed onshore-shelf sedimentary facies from west to east;In Longwangmiao-Xixiangchi period,the basin developed tidal flat-platform-slope sedimentary facies from west to east.

应用多参数划分层内流动单元

大庆油田某井区储集层流动单元采用聚类分析法可划分为E、G和P共3种类型。E类主要对应河道主体带与河口坝砂体,属高孔高渗型储层,综合评分65左右;G类主要对应决口扇与分流间席状砂体,属高孔中渗型储层,综合评分38左右;P类绝大部分对应分流间席状砂体,属中孔低渗型储层,综合评分10左右。3类流动单元的挖潜方向:E类箱型或钟型砂体的顶部易形成剩余油富集区;G类和P类作为二类储层,是下一步挖潜的有利区域。