Paleokarst features and reservoir distribution in the Huanglong Formation of eastern Sichuan

The identification markers of paleokarst have been described in detail and include a combination of surface geology, drilling data and the isotopic characteristics of carbon, oxygen and strontium. The relationships between the vertical zoning, plane distribution and karstification degree of paleokarst and the reservoir development were further analyzed. The study shows that karstic breccias are the most direct sign of paleokarst features. Karsts of different genetic types and the intensity of dissolution have different stable isotopic characteristics from the surrounding cements, and their formation and evolution are significantly influenced by fluid sources, fluid nature and isotopic fractionation. The identification markers of small scale pinholes are quite different from that of large scale holes. The development and evolution of palaeokarsts are mainly controlled by structure, palaeoclimate and lithology. The best lithology for the development of reservoirs is dolomite in the C2hl2 formation. The best zones for the development of the reservoir is located in the upper and lower dissolution intervals of the C2hl2 formation and the best position for the development of reservoir is located in the karst highlands, remnant hills and sloping fields in the karst slope.