A new theoretical model has been developed to describe the chemical reactions of acid in porous carbonate media. For the past 20 years, the three major unanswered questions regarding wormholing when acid is pumped into carbonate formations have been the following: (1) How many dominant wormholes are created? (2) What is the spatial distribution of those dominant wormholes along the wellbore? (3) What is the leakoff profile from the dominant wormholes under radial flow conditions? This paper presents a model that proposes answers to these three basic questions. Once these questions are answered, the reaction of acid in the matrix and the interaction of wormhole development become straightforward. The new model requires a major paradigm shift in the understanding of matrix carbonate acidizing and the variables that control wormhole growth. Parametric studies that were conducted with the new theory are presented. It was found that wormhole length is predominantly controlled by matrix porosity and volume of acid pumped—not by reactivity. It was found that wormhole diameter is predominantly controlled by reactivity and contact time. The new theory confirms classically held guidelines for matrix acidizing of carbonates, and gives insight on how to improve matrix carbonate acidizing treatments. The new model also accommodates the effects of permeability anisotropy caused by natural fracturing or layering effects

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