Shale reservoir fracturing method based on methane multistage burning and explosion

The invention discloses a shale reservoir fracturing method based on methane multistage burning and explosion. Air and supercritical CO2 are used as working fluid, shale reservoir methane is used as fuel, and a reservoir is fractured by utilizing the high pressure effect generated by burning and explosion of a mixture of the air, the supercritical CO2 and the methane so as to realize yield increase transformation of a low-permeability shale reservoir. According to the shale reservoir fracturing method based on methane multistage burning and explosion, a conventional shale reservoir hydraulic fracturing transformation operation mode is expanded to an air pressure fracturing mode, a supercritical CO2 replacement mode and a methane multi-stage burning and explosion multi-fracturing mode, an initial fracture is formed in the shale reservoir through pressing by means of air-supercritical CO2 mixed fluid, and the air distribution concentration in the fracture is adjusted by adjusting the injection flow of supercrit