Single step calcium sulfate scale removal at high temperature using tetrapotassium ethylenediaminetetraacetate with potassium carbonate

Abstract

Calcium sulfate (CaSO4) scale has been identified as one of the most common scales contributing to several serious operating problems in oil and gas wells and water injectors. Removing this scale is considered an economically feasible process in most cases as it enhances the productivity of wells and prevents potential severe equipment damage. In this study, a single-step method utilizing potassium carbonate and tetrapotassium ethylenediaminetetraacetate (K4-EDTA) at high temperature (200 °F) has been used to remove CaSO4 scale. The CaSO4 scale was converted to calcium carbonate (CaCO3) and potassium sulfate (K2SO4) using a conversion agent, potassium carbonate (K2CO3), at a high temperature (200 °F) and under various pH conditions. Various parameters were investigated to obtain a dissolver composition at which the optimum dissolution efficiency is achieved including the effect of dissolver pH, soaking time, the concentration of K4-EDTA, the concentration of potassium carbonate (K2CO3), temperature impact and agitation effect. Fourier transform infrared, X-ray crystallography, ion chromatography, stability tests and corrosion tests were carried out to test the end product of the process and showcase the stability of the dissolver at high temperature conditions. A reaction product (K2SO4) was obtained in most of the tests with different quantities and was soluble in both water and HCl. It was observed that the dissolver solution was effective at low pH (7) and resulted in a negligible amount of reaction product with 3 wt% CaSO4 dissolution. The 10.5-pH dissolver was effective in most of the cases and provided highest dissolution efficiency. The reaction product has been characterized and showed it is not corrosive. Both 7-pH and 10.5-pH dissolvers showed high stability at high temperature and minimum corrosion rates. The single step dissolution process showed its effectiveness and could potentially save significant pumping time if implemented in operation.

Molecular structures of 1-hydroxyethane-1,1-diphosphonic acid for removing calcium sulfate scale under different pH conditions

“…The descaling rate was calculated as follows:where R is the descaling rate (unit in %), X and Y are the scale quality before and after adding solutions with different pH, (unit in g), respectively. 8…”

“…7 Unlike calcium carbonate scale, calcium sulfate scale has a hard texture and compact structure and cannot be directly dissolved by conventional inorganic acid, such as hydrochloric acid. 8 Calcium sulfate scale is considered one of the hardest forms of scale and is difficult to remove. It can damage production equipment, such as pumps, pipes, valves, and heat-exchangers.…”

The Roles of Oil–Water Interfaces in Forming Ultrasmall CaSO4 Nanoparticles

“…However, addressing the problem of CaSO 4 formation presents notable complexities owing to the distinctive attributes of CaSO 4 scales, which exhibit exceptional hardness, adhere robustly to surfaces, and are nearly insoluble in conventional solvents and mineral acids . Moreover, mechanically removing CaSO 4 scale is arduous and potentially damages the substrate . Consequently, mitigation strategies for scaling are crucial to optimizing operational efficacy and curtailing the expense of both oil production and oil spill environmental remediation. , …”

“…11 Moreover, mechanically removing CaSO 4 scale is arduous and potentially damages the substrate. 12 Consequently, mitigation strategies for scaling are crucial to optimizing operational efficacy and curtailing the expense of both oil production and oil spill environmental remediation. 13,14 Examining the solid nucleation process, the initial stage of scale formation, is crucial to understanding mineral scaling.…”