We present 3-D simulations of wormhole formation in carbonate rocks using a two-scale continuum model. We employ the multigrid technique to obtain accurate solution of the model and analyze wormhole patterns in various acidization regimes. We also present a sensitivity analysis of the dissolution process with respect to acid injection rate, dissolution rate constant and rock properties such as initial average permeability, heterogeneity and permeability-porosity relationships. Finally, we determine the wormhole properties such as tip diameter and fractal dimension and compare the simulation results with available experimental data. (C) 2012 Elsevier Ltd. All rights reserved.