Minimizing Calcium Lactate Precipitation Via the Addition of Gluconate Ions for Matrix Acidizing with Lactic Acid

Abstract

Organic acids are commonly used to replace hydrochloric acid (HCl) in high reservoir temperature applications, as they are less corrosive and weaker than HCl. However, organic acids 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. However, 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 term of dissolving calcite, reaction product, corrosion, wettability and generating dominant wormhole. Lactic and gluconic acids were mixed together using deionized water and seawater to conduct calcite solubility tests. Corrosion tests, between 4 and 8 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 run different coreflood tests using different combinations of injection rates and temperatures. These tests were accompanied with analytical results from ICP and 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% and up to 27 wt%. Seawater usage caused calcium sulfate precipitation; therefore, three scale inhibitors were evaluated to determine mitigation rates. Acid calcite-dissolving results were satisfactory when limestone 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 and a trace of iron lactate precipitation occurred at 200 and 300°F. Five gpt from a sulfur-based corrosion inhibitor was enough to mitigate the corrosion rate to allow for eight hours of testing. Wettability alteration was noticeable due to the spent acid interaction with limestone rock and was the highest when high salinity seawater was used. Yet, the addition of corrosion inhibitor showed a reduction in the magnitude of zeta potential change. Coreflood tests showed that the mixture penetrated the tested core with minimal acid pore volume without any face dissolution or salt precipitation on the core faces. 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 which can provide a safe operation environment and can decrease replacement and maintenance costs.

A High Effective Acid System to Stimulate Sandstone Reservoirs

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