Abstract: Reefs are essentially in place calcareous deposits created by sessile organisms. Xisha areas developed thick strata of reef that are formed since the Miocene. Using microscopic and macroscopic observation for the Xike1 well that is fullcoring, combing with paleontology and core test results, we found that Miocene and Quaternary were the main reefbuilding stages in the Xike1 well, then formed two sets of reef succession that is respectively masked by the coralline algae and the coral as the main reefbuilding organism, in which accessory reef organisms are benthic foraminifera. However, Pliocene developed a set of bankfacies deposits. The rock type of this reef succession principally include framestone, boundstone and bafflestone, in which framestones are dominated. Nonreef facies rocks included marlstone, grain limestone and bioclastic limestone. Dolomite formation developed extensively in the Late Miocene to Early Pliocene, which was more caused by the penecontemporaneous dolomitization and affected by hydrothermal activity. Deposition analysis of the reef successions can provide the basic data for oil and gas exploration and distribution of reef reservoir in the South China Sea.

Key words: Xisha areas, reef succession, dolomitization, reefbuilding organism, Xike1 well