Development pattern of palaeokarsts in three ordovician structural belts in the Tazhong Uplift

Aim To discuss the development of paleokarsts and their controlling factors in the central burial hill,slope and platform-edge slope break belts in the Tazhong Uplift.Methods This study is conducted using drilling,core and geophysic data to systematically summarize development of the paleokarst reservoirs in the three structural belts,and to analyze their controlling factors in terms of tectonic evolution,deposition and karst origin.Results The study indicates that the central burial hill belt was tectonically intensive and subjected to intensive karstification.During Ordovician,the central burial hill belt was subjected to the combination of the Caledonian and Hercynian karstifications,but the later filling was also intensive.In the slope belt,tectonic movement was weaker,with stratigraphis sequence well preserved and weaker karstification,the karstification reservoirs occur near the regional unconformities T74 and T72.In the platform-edge slope break belt,upper Ordovician reef bank complex deposition was predominant,providing a sedimentary basis for forming excellent karst reservoirs.The karsts can be classified as weathering and syngenetic karsts,forming karst reservoirs extensively developed along the reef bank strata.The combination of tectonics and deposition controls the development of the karsts in the study area.Conclusion The central burial hill belt is moderately favorable for development of karst reservoirs,which is prevalent over the slope belt with weak karstification and inferior to the platform-edge slope break belt with reef bank karst reservoirs.