In matrix-acidizing long intervals, diversion is essential to obtain good placement of the reactive fluids. Over the years, several diversion techniques have been applied, resulting in improved zonal coverage. These diversion methods can be divided in mechanical methods such as the use of balls to seal the perforations and chemical methods such as gelled fluids.

In the design of matrix acid treatments, placement models that predict the zonal coverage of the fluids are of great help. These models improve the understanding of the complex processes and will help to improve the design of matrix-acid treatments. For studying diversion effects, correct modeling of the diversion methods in a placement simulator is essential. We have developed such a fluid placement simulator (FPS) that contains models for the different diversion methods.

In this paper, we will give an overview of the different diversion methods and their application. Further, we will discuss the implementation of the models in a comprehensive FPS. We will show how this simulator can be used to optimize placement and diversion. Validation of the models will be presented based on the analysis of two case histories.

In an acid treatment, the fluid diversion design is often based on guidelines, rules-of-thumb, and an intuitive idea on how diversion "works." Simulators are not used, usually because they are not available. However, the use of a diversion simulator will show that many of the guidelines and intuitive ideas are wrong, or at least incomplete; this will be illustrated with example calculations.

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