Kinetics of Tertiary Reaction of HF on Alumino-Silicates

Abstract

The standard description of HF acidizing chemistry clearly demonstrates a primary and secondary reaction of HF with alumino-silicates. Field experience has taught our industry that possible precipitation during the secondary reaction can adversely affect treatment success. 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. 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 HCl at temperatures above 250°F. These findings were made possible by recently applied experimental techniques including F NMR Spectroscopy, fractional pore volume flow experiments, and an accurate knowledge of the HF stoichiometry.

A Method for Assessing the Impact of Secondary and Tertiary Reactions on Sandstone Acidizing Treatments

“…Note from Figure 10b that the core permeability continued to increase for about three pore volumes during the injection of 8% NH 4 Cl spacer stage after the 9/1 mud acid stage. A 34% increase in permeability during this period was attributed to cleanup of mobile fines and precipitates generated by the 9/1 mud acid.…”

“…Figure 2 shows a sample of data from slurry reactor tests that were used in determining the reaction kinetics in the geochemical simulator. Shown in the figure are the evolutions of aluminum (Al) and silicon (Si) concentrations in the aqueous phase during dissolution of kaolinite clay with 9/1 mud acid (3) and fluoboric acid (4) . Symbols in the figure are the measured concentrations, while the solid lines are model predictions.…”

“…The function used to compute permeability from porosity changes is (4) In this relation, k and k 0 represent final and initial permeabilities (mD), and φ 0 is the original porosity (%). used in the model is similar to the one proposed by Labrid [20].…”

“…In addition to dissolving the fines, it was also desirable to include some form of clay stabilization to extend the production gains over a longer period of time than with the previous treatments. The chemical options available for dissolving fines and simultaneously stabilizing clay are all fluids containing HBF 4 . As these fluids are not compatible with carbonates, an appropriate volume of an acid preflush must be injected to remove the carbonates near the wellbore.…”

“…Les résultats de ces études ont fourni l'information nécessaire à la mise au point des traitements. Due to their importance in determining the outcome of matrix stimulation treatments, secondary and tertiary reactions have been extensively described in the literature [2][3][4]. However, the extent of these reactions under reservoir conditions remains difficult to quantify.…”