Characteristics and formation mechanism of talc in Permian Maokou Formation, southwestern Sichuan Basin: a case study of first member of Maokou Formation in well A1

Different forms of talc have been developed in the first member of Permian Maokou Formation (P2m1) in the Sichuan Basin. As a hydrothermal alteration mineral, its formation mechanism and its influence on the P2m1 reservoir need to be further explored. The talc of P2m1 in the southwestern Sichuan Basin was studied by means of core observation, thin section identification, scanning electron microscope, and the homogenization temperature of fluid inclusions. Based on the detailed description of the color, structure and occurrence state of talc, the formation mechanism of talc was discussed. The talc of P2m1 mainly occurs in micrite bioclastic limestone, bioclastic micrite limestone and limestone dolomite, or in micrite limestone as metasomatic bioclastic particles or star points. The genetic mechanism of talc is metasomatism between siliceous hydrothermal fluid and magnesium-rich carbonate rocks under certain conditions, which belongs to hydrothermal metasomatism. There is a positive correlation between the content of talc and the physical properties of reservoir. Large amount of acid gas (CO2) may be generated during the formation process of talc, which was favorable for the dissolution and pore preservation of P2m1 and finally to improve the reservoir capacity. The existence of talc may be indicative for the migration path and distribution of silicon-bearing fluid, and the hydrothermal high energy area is favorable target for further exploration.