Kinetics of the Primary Reaction of HF on Alumino-Silicates

Abstract

Abstract 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