High-concentration HF treatment

Little has been published in support of acidizing with high-concentration HF, which opposes conventional guidelines. However, there is some evidence that high-concentration HF treatments can be effective in certain sandstone formations. 

High-concentration HF means a concentration that is high relative to conventional wisdom—not concentrated HF, by any means. For example, high-concentration HF mixtures contain 5%, 6%, or maybe even 9%-10% HF in combination with HCl, HCl-organic mixtures, or other proprietary organic-based acids. 

The only way to determine the benefit of using a high-concentration HF mixture in a conventional procedure is through core flow testing with the actual formation core of interest. At present, the complex combination of formation and mineralogical properties that lend themselves to high-concentration HF treatments cannot be accurately predicted. 

More often than not, higher HF concentrations, in combination with excess HCl, will be damaging to rock competency. This can lead to nearwellbore formation failure, possibly to sloughing in perforations, and 

Low-strength HCl/flexible strength HF (up to 6%) + organophosphonic acid complex, using coiled-tubing/jetting-nozzle placement and/or on-the-fly chemical diversion 

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First, handling of highly concentrated acids, including hydrofluoric acid, especially at elevated temperatures, is very dangerous and requires use of special equipment and appropriate training of personnel. Second, the required amount of fluorine (or HF) is well above the amount needed based on the interaction stoichiometry. This results in large amounts of liquid waste, the treatment of which is very expensive. 

The control shows intense a (peaks 1-1, 1-2, 2-2) class isoenzymes with the p (peaks 3-3, 3-4, 4-4)class at lower intensity. BT and HF treatments altered the profile in such a way that the relative intensity of the a and p isoenzymes has changed. Both compounds induced the p class of isoenzyme, in particular 3-3 and 3-4 at high concentration. It is important to note the relative intensity of these peaks. It appears that the induction of the p class of isoenzyme may be more closely associated with the inhibition of carcinogenesis than that of the a class. 

For determinations in glass, dissolution of the matrix by treatment with HF and subsequent analysis of the trace concentrate is certainly a feasable approach. In high-quality glasses used e.g. for the production of fibers, even very low concentrations of trace elements may be relevant, so hydrofluoric acid of very high purity has to be used for the sample decomposition. This can be obtained by sub-boiling procedures in plastic apparatus. 

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