Method for calculating porosity of shale gas reservoir by element logging

The invention provides a method for calculating the porosity of a shale gas reservoir by element logging, which comprises the following steps of: inversely calculating the mass fraction of each mineral according to the mass fraction of reservoir elements measured by element logging and the molecular formula of the mineral in the reservoir; calculating the total organic carbon content in the reservoir according to a nickel element content fitting curve measured by element logging; and calculating the porosity of the shale gas reservoir on the basis of quartz, calcite, dolomite and clay in reservoir minerals according to different total organic carbon contents. According to the method, the content of each mineral component is calculated through inversion of the element content measured by element logging, the porosity of the shale gas reservoir is calculated by calculating the total organic carbon content and taking the related mineral components as the basis, the calculation result error is small, the evaluati