1. A method for estimating a porosity of a subterranean region, the method comprising: accessing a nuclear magnetic resonance (NMR) relaxation distribution corresponding to NMR measurements of a subterranean region, the NMR relaxation distribution comprising a plurality of peaks; using a data processing apparatus to fit a plurality of Gaussian functions to the NMR relaxation distribution to establish values for fitting parameters for each of the Gaussian functions; determining the porosity of the subterranean region based on the values of the fitting parameters of the Gaussian functions; and categorizing the porosity based on a relationship between the fitting parameters of the Gaussian functions and a distribution of pore sizes.