Experimental dissolution and karst strata association of Middle Permian Maokou carbonate rocks in the northern part of Sichuan Basin

Kart reservoir is important for the Middle Permian Maokou Formation in the northern part of Sichuan Basin. Based on field outcrops and drilling core data, combining both macro and micro methods, the characteristics of karst strata association of the Maokou Formation in this area was studied by the means of thin section observation, scanning electron microscope, major and trace elements and experimental dissolution. The first member of the Maokou Formation is dominated by marl and bioclastic micritic limestone, and the content of acid insoluble matter is high. The second and third members of the Maokou Formation are dominated by micritic bioclastic limestone and bright crystal bioclastic limestone, and the content of acid insoluble matter is low. The results of dissolution experiments show that the mineral type and chemical composition of carbonate rock are the main factors affecting the solubility of rock. The change characteristics of the dissolution rate of samples, solution ion concentration and micro dissolution are as follows: bioclastic limestone>micrite limestone>dolomite>argillaceous limestone. The karst strata association types of the Maokou Formation can be divided into 2 groups, 3 types and 9 subtypes. The karstification conditions and rock dissolution degree of different karst formation types are different, and the development scale of fracture cave karst reservoir is also different.