The overall sedimentary environment of the Mid-Triassic Leikoupo Formation in the Northeastern Sichuan Basin is dominated by evaporite platforms where a set of thick and wide-spreading evaporites predominantly of gypsums and dolomites were deposited.The Leikoupo Formation can be subdivided into four members.The seismic responses of the fourth member feature in weak amplitude

low frequency and relatively continuous reflection configuration.Most reservoir rocks within the fourth member are type-III of low permeability

some of them show characters of type-II.Their pore spaces are dominated by caverns

dissolution-widened fractures and structural fissures.The development and distribution of the reservoir rocks in the member were controlled by both sedimentary facies and weathered crust.Dolomites of platform evaporate facies and lagoon facies in the study area were exposed and eroded into weathered crust during the last period of the Leikoupo Formation deposition.In addition

the dolomites also experienced leaching and corrosion of meteoric water along unconformities and fractures

resulting in a set of high-quality reservoir rocks.