A model to estimate the permeability of a porous sample based on a 3D Image of its pore space, obtained by X-ray computed tomography (CT) and applying a threshold algorithm on the CT image, is developed Computational fluid dynamics (CFD) can be used to directly compute the saturated fluid flow in a sample This is called the direct method The direct method is relatively accurate, but computationally very expensive Therefore, a new pore network approach is presented Pore networks simplify the pore space to a network of nodes that are hydraulically connected by links A finite difference CFD method is then applied to simulate the fluid flow inside the links and to compute the local permeability values of the links in the network according to Darcy's law As these links are relatively small, this demands less computational resources than a CFD simulation on the whole sample Once the local permeabilities in the network are known, the permeability of the entire network can be calculated