A method is disclosed for determining the connectivity architecture of a hydrocarbon reservoir in terms of locally optimal paths between selected source points, e.g. wells. In one embodiment of the invention, a fast-marching method (133) is used to compute the distance field (or the time of arrival field) from N selected source points in a heterogeneous media, i.e. in a non-uniform velocity field. This is done by propagating N labeled (132) fronts simultaneously from N objects. Then, a method (134) is disclosed for detecting Voronoi curves or Voronoi surfaces, where fronts of differing labels meet each other. Then, saddle points are found on the Voronoi curves or surfaces (135), and each saddle point is used to determine a locally optimal path (136) between a pair of equidistant (from the saddle point), closest (to the saddle point) source points.