Kinetics of the Primary Reaction of HF on Alumino-Silicates

Abstract

SummaryThe standard description of HF acidizing chemistry clearly demonstrates a primary and secondary reaction of HF with alumino-silicates.1–6 Field experience has taught our industry that possible precipitation during the secondary reaction can adversely affect treatment success,7,8 especially in formations with high K-feldspar content9 or temperatures above 300°F. Recent work has also been reported on the existence of a third, or tertiary reaction of HF with alumino-silicates.10In this paper determination of the rate law and kinetics for the primary reaction of HF on sand, clay, and feldspar over a broad temperature range is reported. The rate law for the primary reaction of HF with sand had no HCl 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 HCl 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 nuclear magnetic resonance (NMR) spectroscopy,10 fractional pore-volume flow experiments,11 and an accurate knowledge of the HF stoichiometry.12 Laboratory findings have been verified through detailed analyses of flowback samples from field treatments.13