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Qualitative study on the potential of lactic and gluconic acids for acidizing operations
Alhamad, Luai
Alhamad, Luai
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2020
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Abstract
Organic acids are commonly used to replace hydrochloric acid (HCl) in high temperature reservoir applications, as they are less corrosive and weaker than HCl. However, organic acids are weaker than HCl and have shown some problems due to acid reaction product solubility. One such organic acid, lactic acid, produces calcium lactate when it reacts with calcite, which has a low solubility in water. Nevertheless, reaction product solubility can be improved by up to five times when gluconate ions coexist with lactate and calcium ions. The objective of this research is to evaluate lactic and gluconic acid mixtures in terms of dissolving calcite, reaction products, corrosion, wettability and generating dominant wormholes.Lactic and gluconic acids were mixed together using both deionized water and seawater to conduct calcite solubility tests. Corrosion tests, between 4 and 12 hours, were also run under reservoir conditions. Zeta potential measurements were performed to determine alterations in rock wettability. A formation response test (FRT) apparatus was used to perform different coreflood tests using different combinations of injection rates, total acid concentrations, and temperatures. These tests were accompanied with analytical results from inductively coupled plasma (ICP) and ion chromatography (IC) to measure calcium, iron and sulfate ions in solution.The results showed that mixing lactic and gluconic acids at a 1:1 molar ratio provided the optimal results as no precipitation occurred at total acids strengths of 10 wt% to 33 wt%. Seawater usage caused calcium sulfate precipitation; therefore, three scale inhibitors were evaluated to determine mitigation rates. Acid calcite dissolving results were satisfactory when calcite was exposed to a 1:1 and 2:1 molar ratio of crushed core-to-acid ratios, as at least 50% of the crushed core was dissolved. However, the two-acid mixture showed a corrosion rate that was higher than the acceptable rates at 200 and 300°F where a trace of iron lactate precipitated at 300°F. Five gpt from a sulfur-based corrosion inhibitor was enough to mitigate the corrosion rate to allow for twelve hours of protection.Wettability alteration was noticeable due to the spent acid and the used additives interaction with calcite particles. The zeta potential study showed the importance of following the common practice of including a mutual solvent in the treatment to lower the negative impact of acids and additives.Coreflood tests showed that the lactic and gluconic acid mixture penetrated the tested core with minimal acid pore volume without any face dissolution or salt precipitation on the core faces. However, maintaining the optimum total acid concentration, injection rate, and temperature was important to deliver the optimum results. These parameters had a direct effect on the produced dissolution pattern and the minimum required pore volume to breakthrough.This research presents a set of diverse experimental data to confirm lactic acid accompanied by gluconic acid can penetrate carbonate formation without any by-product precipitation. The two organic acids are less corrosive and less hazardous than HCl and can provide a safe operation environment, while decreasing replacement and maintenance costs.
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