RESERVOIR CHARACTERISTICS AND SEISMIC IDENTIFICATION IN CARBONIFEROUS BURIED HILL IN SOUTH CHINA SEA

Carboniferous carbonate in the basement of A depression in South China Sea has suffered the weathering and erosion actions for long geological ages during Permian-Cretaceous,hence,a lot of favorable carbonate karst reservoirs are developed there.However,further exploration has always been constrained by the complexity of the karst reservoir development in carbonate buried-hill.Based on the classification and comparison of the karst reservoirs,the paper concluded that the karst reservoirs in this region could be classified into Epikarst zone,vadose karst zone and underflow karst zone.The reservoirs are primarily composed of solution vugs,cavities and structural fractures,among which solution vugs and cavities are the main storage spaces while structural fractures mainly play roles connecting the matrix pores,solution vugs as well as cavities,and improving the infiltration of reservoirs.By using drilling information to calibrate the karst reservoir,it is concluded that Epikarst zone is characterized by weak amplitude,weak connectivity(low coherence)and low impedance while the inner reservoir is characterized by minor phase axis,strong amplitude,high energy and low impedance,therefore,the karst reservoirs can be i-dentified with seismic attributes.