Acid fracture stimulation generates higher well production but requires engineering design for treatment optimization. To quantify the cost and benefit of a particular acid fracture treatment an engineer must predict the resulting fracture's conductivity distribution. Current practice is to estimate conductivity distribution utilizing two-dimensional models. Unfortunately, these models can misrepresent the amount of acid etching upon which the conductivity estimation is based.A new modeling tool has been developed to estimate fracture conductivity and is used to evaluate different acid fracture treatment designs. The tool uses three-dimensional flow simulation to resolve acid transport in a fracture. This approach includes resolution of the three-dimensional fluid velocity throughout the fracture, fluid pressure, the acid concentration profile, and the acid-etched width. By using a fine grid in the direction of transport to the fracture surfaces, convective and diffusive transport of acid to the fracture surfaces are modeled. The acid-etched width distribution and other formation information are used to calculate the resulting conductivity distributions for different treatment designs.The output acid-etched width and conductivity distributions for different acid fluid systems, fracture geometries, geologies, and completion designs are calculated. The industry lacks a reliable tool for acid fracture treatment design. The modeling tool presented in this paper attempts to address this problem with rigorous simulation of acid transport and etching in a fracture. The parametric study illustrates the benefits and drawbacks to this approach.