A method includes screening heterogeneity of a rock sample using nuclear magnetic resonance testing to determine a composition of the rock sample, drilling at least one smaller rock sample representative of the determined composition, and testing the at least one smaller rock sample with mercury- injection capillary pressure to obtain a. capillary pressure distribution (52) of the at least one smaller rock sample. The method further includes decomposing a T2 distribution (54) from the nuclear magnetic resonance testing and the capillary pressure distribution (52) using Gaussian fitting to identify multiple pore systems (58, 50, 59), where the small ends (51, 53) of the Gaussian fitted T2 distribution (54) and the Gaussian fitted, capillary pressure distribution (52) are overlapped for at least one of the identified pore systems (50).