Corrosion Inhibition of Hydrochloric - Hydrofluoric Acid/Mutual Solvent Mixtures at Elevated Temperatures
Authors: Woodroof Robert A. , Baker James R. , Jenkins Robert A. 
Published: December 2007

This paper was prepared at the 50th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Dallas, Texas, on Sept. 28-Oct. 1, 1975. Permission to publish is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon requested to the Editor of the appropriate journal, provided agreement to give proper credit is made.
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Abstract
The use of hydrochloric-hydrofluoric acid mixtures for the matrix treatment of sandstone reservoirs has been a successful stimulation technique for over a decade. A more recent development has been the addition of mutual solvents, such as ethylene glycol monobutyl ether, to these binary acid mixtures. While improving the downhole acid treatment performance, the mutual solvents also rendered the commercially available acid corrosion inhibitors much less effective at elevated temperatures.
The mutual solvent have been observed to alter the dispersibility and inhibitor film deposition properties of commercially available acid corrosion inhibitors, thus creating a need for new or modified corrosion inhibitors for these HC1-HF mutual solvent systems. The development of such an inhibitor is described as are the effects of varying test temperatures, types of mutual solvents employed, HC1-HF ratios, binary acid-mutual solvent ratios, and grade of tubular goods tested. Knowledge gained from these laboratory studies will not only help insure the more efficient use of this and similar acid corrosion inhibitors, but will also provide insights for the future development of even more effective high temperature corrosion inhibitors for these HC1-HF/mutual solvent systems.

Introduction
The use of hydrochloric acid to increase oil production from limestone formations was described production from limestone formations was described by Herman Frasch as early as 1896. It was not however, until early 1930's when suitable hydrochloric acid corrosion inhibitors were developed, that commercial acidizing of limestone formations was offered to the oil industry.
The success of acid stimulation of limestones raised interest as to the effectiveness of similar treatments in sandstone stimulation with hydrochloric-Hydrofluoric acid mixtures proved unsuccessful. Reintroduced in 1939 as "Mud Acid", designed for removing residual drilling mud solids and restoring natural permeability through restoration of undamaged flow channels in the vicinity of the wellbore, the hydrochloric-hydrofluoric acid mixtures experienced only limited application due to numerous unsuccessful field tests and insufficient understanding of the chemistry of hydrofluoric acid reactions in sandstone.