W.C. David Fry, C.L. Boney, J.W. Atchley, & F.T. Whitsett, Dowell Division of Dow Chemical Co.
Hydrochloric acid has been used for more than 40 years to improve production in oil and gas wells. Many techniques have been used to improve results of hydrochloric-acid treatments. One of the most important advances has been recognition that fracturing occurred during the majority of acidizing treatments. This enables the use of fracturing principles to increase live acid penetration. Unfortunately, actual results did not correlate with predicted results. This prompted the use of many techniques to improve results. Some of these are listed below. 1. Acid retardation 2. Increased acid concentration 3. Increased injection rates 4. Increased fracture width to decrease area-to- volume ratio 5. Improved matrix leakoff control 6. Increased pad volumes 7. Improved computer programs. All of these approaches had the purpose of increasing live acid penetration, and thus improving conductivity to the wellbore. Although each action helped either separately or when used in various combination, still a large gap remained between predicted and actual results. The problem has been that the work was based on the assumption that leak off was due to matrix permeability.