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.

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