Karstification of Ordovician Strata in Western Tazhong Area of Tarim Basin,Xijiang

There exist thick marine carbonate strata of varied lithologic characters in the Lower Ordovician-Upper Ordovician Lianglitage Formation of western Tazhong area. Based on data of drill cores, logs and laboratory tests, the authors recognized three types of karstifications in the study area, namely syn-depositional, weathering-crust, and buried ones. The syn-depositional karstification occurs mainly on the platform margin of Later Ordovician Lianglitage Formation, in which atmospheric lithogenic lens are frequently seen but their sizes are not so big. The weathering-crust karstification is developed in central Kartarke uplift. The buried karstification can be divided into three stages and are distributed in areas where faulted structural belts and igneous rocks are well developed. Lithofacies and sedimentary facies, karstification and structural fissures are main factors controlling the development of Ordovician carbonate reservoirs, which constrain the development of karst reservoir rocks in different layers and positions.