The 3D Unified Pipe-Network Method (UPM) is applied to simulate the acidizing process in fractured carbonate rock. Fractures and porous media are represented by their equivalent connected fracture pipes and matrix pipes, respectively. The UPM combined with a two-scale continuum model is a numerical approach to wormhole development. Benchmark tests are attempted against commercial software and a sensitivity analysis is carried out with respect to the rock porosity heterogeneity magnitude and injection rates. The influences of the geometric properties and permeability of a fracture on wormhole propagation and the amount of reaction fluid per pore volume required to reach a breakthrough (PVBT) are analysed.