Sedimentary facies of Carboniferous carbonate rock in Bashitop Oil Field, Tarim Basin

In Bashitop area of the Tarim Basin,from bottom to top,Carboniferous can be divided into 3 formations:Bachu,Kalashayi and Xiaohaizi.Sedimentary facies of the study area are carbonate platform,which may be further divided into 3 subfacies including evaporated,restricted and open ones.Carbonate rocks are very common,interbedded with clastic and gypsum rocks.During the late Bachu period,terrigenous detrital supplies decreased and a set of carbonate rock rich in biodetritus was formed,and the restricted platform subfacies was deposited.During the early and middle Kalashayi period,the study area was dominated by evaporated and restricted platform subfacies while in the late Kalashayi period,it turned to restricted platform.In the Xiaohaizi period,open platform spread in most of the study area.Due to the cyclicity of sea level change,all microfacies lie in rule and form reservoir-seal assemblages.3 above-mentioned assemblages have been found in Carboniferous,2 in the Xiaohaizi Formation and 1 in the Bachu Formation.Petroleum in the Xiaohaizi Formation mainly locates around well BK4H,M4 and M6.Petroleum in the Bachu Formation mainly locates around well M10,BK4H and M6.