Method and device for optimizing well closing time after shale gas well fracturing

The invention discloses a method and a device for optimizing well closing time after shale gas well fracturing. The method comprises the following steps: according to a numerical simulation result, through a pressure distribution calculation model caused by fracturing fluid injection, determining a first relationship of a pressure boundary line movement rate along with the change of well closing time; according to the numerical simulation result, on the basis of the gas diffusion theory, a second relation that the gas-water ratio change rate generated in the shaft after the shale gas well is fractured and the fracturing fluid is injected changes along with the well closing time is determined; determining the optimized well closing time after the shale gas well is fractured according to the first relation and the second relation, specifically, determining the first well closing time when the pressure boundary line movement rate begins to be lower than a set rate threshold value according to the first relation,