Methods and systems method for determining core permeability of a subsurface formation. The method includes connecting an upstream reservoir to one end of a sample holder comprising a core sample of a subsurface formation, connecting a downstream reservoir to another end of the sample holder, providing a constant confining pressure within the sample holder, saturating the sample holder and the core sample with nitrogen at a saturation pressure, applying a pressure pulse to one end of the sample holder, and determining core permeability using the porosity of the mobile continuum when the pressure in the upstream reservoir, the downstream reservoir, and the mobile continuum is in equilibrium.