Kinetics of the primary reaction of HF on alumino-silicates

The standard description of HF acidizing chemistry clearly demonstrates pri mary and secondary reaction of HF with alumino-silicates.(1-6) Field experi ence has taught our industry that possible precipitation during the seconda ry reaction can adversely affect treatment success,(7,8) especially in form ations with high K-feldspar content(9) or temperatures above 300 degreesF. Recent work has also been reported on the existence of a third, or tertiary reaction of HF with alumino-silicates.(10) In this paper determination of the rate law and kinetics for the primary re action 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 p rimary reaction of HF with clay and feldspar was assumed to also have no HC l dependence and was adequately described by a first order in HF concentrat ion. In addition, a mass transfer equation for reactive fluids flowing thro ugh porous sandstone media is proposed. These findings were made possible b y recently applied experimental techniques including F-19 nuclear magnetic resonance (NMR) (10) fractional pore-volume flow experiments,(11) and an sp ectroscopy, accurate knowledge of the HF stoichiometry.(12) Laboratory find ings have been verified through detailed analyses of flowback samples from field treatments.(13)