Organic-HF blends have successfully stimulated sandstone formations with corrosion concerns, HCl-sensitive mineralogy, and/or crude oil incompatibilities, three conditions in which the use of typical HCl-based fluids can result in severe damage. Despite the success of such blends, very little work has been published on the reactivity of organic-HF fluids with aluminosilicates. Recent work on the chemistry of HF acidizing focused on HCl-HF systems.1 This paper discusses the chemistry of organic-HF systems as determined by laboratory reactivity tests, 19F nuclear magnetic resonance (NMR) studies, and organic-HF flowback analyses.
Laboratory reactivity testing revealed severe precipitation problems associated with the currently used acetic-HF and formic-HF systems. Flowback analyses after organic-HF field treatments fully supported the laboratory results. A 19F NMR spectroscopic study of the fluoride distribution throughout the primary, secondary, and tertiary reactions helped explain the precipitation and when it might occur. From this work, new organic-HF systems were developed that prevent precipitation while maintaining all the advantages associated with the acetic-HF and formic-HF fluids. The retarded nature of these systems is discussed in this paper.