Comment on: From pore scale to wellbore scale: Impact of geometry on wormhole growth in carbonate acidization

During the dissolution of porous rock, positive feedback between fluid transport and mineral dissolution leads to the spontaneous formation of pronounced wormhole-like channels. In a recent paper, Cohen et al. (2008) analyzed wormhole growth and competition in a dissolving porous rock, using a Darcy-scale numerical model developed by Golfier et al. (2002). In particular, they analyzed the competition between wormholes, which hinders the growth of shorter channels and leads to the emergence of a hierarchical structure, with many short wormholes, and only a few long ones. By analyzing the distribution of wormhole lengths (reproduced in Fig. 1) they found evidence for the existence of a characteristic length d ≈ 5cm, at which a change in slope occurs. They concluded that the wormhole competition process is not completely scale invariant. The length scale d was interpreted as marking a transition to a regime where the interplay of diffusion and convection of reactant within a wormhole plays a decisive role in its growth.