The standard description of HF-acidizing chemistry clearly demonstrates a primary and secondary reaction of HF with alumino-silicates.1  Field experience has taught our industry that possible precipitation during the secondary reaction can ad-versely affect treatment success,2  especially in formations with high K-feldspar content or temperatures above 300°F. Recent work has also reported the existence of a third, or tertiary reaction of HF with alumino-silicates.3 

This paper reports the determination of the rate law and kinetics for the primary reaction of HF on sand, clay, and feldspar over a broad temperature range. The rate law for the primary reaction of HF with sand had no HC1 dependence and was second-order in HF concentration. The rate law for the primary reaction of HF with clay and feldspar was assumed to also have no HC1 dependence and was adequately described by a first-order in HF concentration. In addition, a mass transfer equation for reactive fluids flowing through porous sandstone media is proposed. These findings were made possible by recently applied experimental techniques including 19F NMR Spectroscopy,3  fractional pore-volume flow experiments4  and an accurate knowledge of the HF stoichiometry.5  Laboratory findings have been verified through detailed analyses of flowback samples from field treatments.6 

You can access this article if you purchase or spend a download.