Kinetics of Tertiary Reaction of HF on Alumino-Silicates Available to Purchase

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 adversely affect treatment success.²  This statement has been particularly true in formations with high K-feldspar content or formations having 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 how the rate law and kinetics for this tertiary reaction are determined on kaolinite and feldspar over a broad temperature range. This document also discusses the discovery of how most clays were thermally unstable to HC1 at temperatures above 250°F. These findings were made possible by recently applied experimental techniques including ^l9FNMR Spectroscopy,³  fractional pore volume flow experiments,⁴  and an accurate knowledge of the HF stoichiometry.⁵ 

The tertiary reaction of aluminum fluorides, AlF_x (where x is the average F/Al ratio), with clay was slow below 200°F and was dominated by HC1 decomposition of the clay above 250°F. The tertiary reaction required the presence and consumption of acid to proceed. Feldspars were very stable in HC1 at all temperatures while every clay tested had a temperature above which it was easily decomposed by HC1. Ion-exchanging clays tended to be the least stable of the clays, while kaolinite was the most stable clay.