A fully 3D modeling tool to evaluate and predict acid fracture performance across the wide range of carbonate field properties has been developed. The model simulates acid transport and fracture face dissolution. The acid transport model includes the non-Newtonian characteristics of most acid fracturing fluids, the solution of the 3D velocity and pressure fields, and diffusion of acid toward the fracture surface. The acid reaction algorithm permits live acid to leakoff and react within the rock matrix, forming wormholes that update the leakoff boundary condition for each time step. The acid fracture model utilizes commercial 3D fracture propagation software to define the physical domain of the acid fracture simulation.
The performance of an acid fracturing treatment is quantified with conductivity, which is strongly dependent on the etched width created by the acid. The model numerically solves equations describing 3D acid transport and reaction within a fracture to yield the etched width created by acid along the fracture. This conductivity is calculated with the simulator derived acid-etched width, using correlations recently developed that reflect the small scale heterogeneity of carbonate rock as it creates etching along the fracture surface. A case is presented typical of industry practice that demonstrates the model capabilities.