Calcium Sulfate Dissolution Using Lactic Acid

Abstract

Abstract There has been a global surge in scale challenges across the oilfield industry, surpassing other flow assurance challenges. In principle, scale refers to the deposition of mineral solids (primarily inorganic), such as calcium carbonate, calcium sulfate, or barium sulfate, that can accumulate and obstruct flow pathways in various industries, including oil and gas production, water treatment, and other industrial processes. Scale formation can lead to reduced production rates, increased energy consumption, equipment damage, and operational disturbances. Hence, the mitigation and prevention of scale deposition have become pivotal for maintaining high-performing production processes. In this regard, among the known scales, the calcium sulfate scale, in the form of gypsum (CaSO2.2H2O), is deemed challenging for many applications. This type of scale is usually caused by mixing incompatible waters. CaSO2.2H2O is an acid-insoluble scale; thus, it requires an effective scale dissolving recipe. Herein, we demonstrate the use of lactic acid (C3H6O3) as an emerging green chemical to remove gypsum deposits in the presence of different bases, including potassium and sodium carbonates and hydroxides. Different scale removal recipes were developed comprising mixtures of lactic acid with individual bases or a mixture of two bases. We show that, generally, hydroxide bases have exhibited lower performance, particularly potassium hydroxide, compared to their carbonate counterparts. Nonetheless, potassium carbonate, in particular, has offered a better performance compared to sodium carbonate. Incorporating lactic acid with the experimented bases has further improved the performance of the developed recipes, thanks to the induced synergistic effect, specifically with potassium carbonate. The latter has also demonstrated the ability to polymerize lactic acid when coupled with another base, such as sodium hydroxide or potassium hydroxide. Noteworthy, using sodium carbonate has resulted in much lower performances when coupled with the other hydroxide bases. Therefore, mixing two bases when dissolving calcium sulfate is not always the optimum choice as it brings other negative consequences.