Abstract
Hypothesis
Depending upon the matrix composition near a CO2 injection well, the mineralogy may be acid soluble. This study presents a discussion on the expected changes to the near well bore mineralogy in carbonate formations. A tartaric acid pre-wash is tested to determine if it can prevent dissolution of the matrix in an acidic environment.
Experiments
Calcium carbonate, ground and sieved to about 250μm, was used to study the impact of acidified (pH∼3) brine on carbonate formation material similar to near well bore conditions. The calcite was tested in stirred batch systems (at atmospheric conditions of 1 atm and approximately 25°C) in solutions containing 0.015, 0.08, and 0.15M meso tartaric acid. One experiment also involved gas phase CO2 being sparged in the solution to generate an elevated CO2 content environment. pH was monitored to determine extent of dissolution that occurred; these results were verified by solution composition and SEM images of the calcite grains.
Findings
The results of batch experiments conducted herein show that a meso tartaric acid at 3 pH will form a coating over the calcite in-situ, dramatically reducing the overall dissolution of the carbonate mineral, even at extremely sub-saturated conditions. SEM images and aqueous analysis show the fastest layer formation at the highest tested concentration of 0.15 M meso tartaric acid, with similar but less inhibition observed at 0.08M and 0.015M treatment levels. The calcite saturation index was about SI= −10, while calcium tartrate SI was 0; this confirms that the system was in equilibrium with the precipitated calcium tartrate while highly subsaturated with calcite.
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