During the past few years, concentrated hydrochloric acid has proved to be superior to less concentrated acid in providing improved etch patterns and deeper live acid penetration. In deeper, hotter wells (300 penetration. In deeper, hotter wells (300 degrees F) adequate inhibition of the acid becomes a problem. Various organic acids and HCl-organic acid mixtures have been used effectively, but results are comparable to those expected from 15-per cent HCl.
Recent laboratory studies have been conducted to determine the properties of the commonly used "retarded" acid systems required for treating high-temperature formations. Results indicate the boost in acid concentration from adding an organic acid to HCl is largely offset by a kinetic limitation of reaction whereby carbon dioxide formed by the primary reaction of the acid with limestone prevents complete reaction of the organic acid. Thus, addition of 5 per cent organic acid will result in a reaction of only 2 per cent to 3 per cent of this acid until the carbon dioxide is removed from solution by pressure release.
Concentrated HCl provides the distinct advantage of improved etch pattern and deeper live acid penetration. The world's record producing gas well (Hunton Lime) was acidized producing gas well (Hunton Lime) was acidized with 28 per cent HCl. BHT was in excess of 300 degrees F. The problem with 28 per cent HCl is adequate inhibition. Arsenic inhibitors are ineffective in HCl above 17 per cent concentration. Organic inhibitors give two hours protection so their use with concentrated HCl requires the use of a water pad to cool the pipe. No corrosion pad to cool the pipe. No corrosion problems have been encountered with this problems have been encountered with this technique, but the use of concentrated acid with its limited inhibition leaves small room for error.