Understanding Wormholing Mechanisms Can Improve Acid Treatments in Carbonate Formations

Summary In this paper, acid wormholing in carbonate formations is studied. The wormhole growth rate and the geometry of the final worm-hole pattern depend on the combined effect of acid spending and fluid flow. Acid spending is studied by modeling the wormhole as a cylindrical pore and numerically solving the convection-diffusion equations. A finite acid-rock reaction rate is assumed, allowing calculation and study of spending profiles in both the diffusion-controlled and the reaction-controlled regime. Flow properties such as fluid loss from wormhole to formation and fluid distribution in a multiple wormhole geometry are studied through numerical simulations. It is shown how wormhole growth properties are affected by the length and distance of neighboring worm-holes. The effect of injection rate and diffusion is studied with a simple model. This model explains several experimentally observed phenomena, such as the existence of an optimum injection rate and a reduced wormhole efficiency at higher rates.