| dc.description.abstract | Iron precipitation during matrix acidizing treatments is a well-known problem. During matrix acidizing, successful iron control can be critical to the success of the treatment. Extensive literature review highlighted that no systematic study was conducted to determine where this iron precipitates, the factors that affect this precipitation, and the magnitude of the resulting damage.
Iron (III) precipitation occurs when acids are spent and the pH rises above 1, which can cause severe formation damage. Chelating agents are used during these treatments to minimize iron precipitation. Disadvantages of currently used chelating agents include limited solubility in strong acids, low thermal stability, and/or poor biodegradability.
In this study, different factors affecting iron precipitation in Indiana limestone rocks were examined. Two chelating agents, GLDA and HEDTA, were tested at different conditions to assess their iron control ability.
Results show that a significant amount of iron precipitated, producing a minimal or no gain in the final permeability, this indicated severe formation damage. The damage increased with the increase of the amount of iron in solution. When chelating agents were used, the amount of iron recovered depended on both chelate-to-iron mole ratio and the initial permeability of the cores. Calcium is chelated along with iron, which limits the effectiveness of chelating agents to control iron (III) precipitation. Acid solutions should be designed considering this important finding for more successful treatments. | en |
