It is recognized that the Yingshan Formation was in eogenetic stage both in depositional and exposure period according to the tectonic evolution history in Tazhong area.Based on a large amount of image logging

cores

thin sections

geochemical data and 2D & 3D seismic data in combination with cathode luminescence

scanning electronic microscope and seismic attributes extraction

we identified two types of eogenetic karst in the Yingshan Fm.in northwestern Tazhong area

namely mixing water karst and meteoric karst

discussed their formation characteristics and built karstification models.The following results were obtained.①The mixing water karst was formed by fabric-selective dissolution and controlled by high-energy sedimentary facies in coastal regions and occurs mainly in Well Shun7 in northern slope break zone;②The meteoric karst was produced by non-fabric-selective dissolution

and is universal in areal distribution.Karst reservoirs are dominated by fractured reservoirs and fractured-vuggy reservoirs.The karst is incomplete in vertical architecture and the reservoirs are insignificant in differential characteristics in respect of paleogeomorphology and are controlled by the NWW-trending fault system.The karstification mode is “fissure-seepage” type in an open system under the control of low relief paleogeomorphology.