Iron scales can also be removed using HCl and a sequestering agent. Other acid-soluble scales are iron carbonate, iron sulfide and iron oxide (Fe 2O 3). Calcium carbonate can be removed using hydrochloric acid, acetic acid, formic acid or sulfamic acid. Calcium carbonate, for example, is a soluble acid scale. Acid soluble scales are the most common type of scale. Sodium chloride is an example of a water-soluble scale that does not recommend dissolved using acid. Chemically reactive scales are classed according to their solubility in water, acid, or chemicals other than water or acid. Due to the insoluble nature of chemically inert scales in other chemicals, mechanical means must be utilized to remove this type of deposit. Scales are categorized according to their mechanism of removal. Scales caused by calcium carbonate, calcium sulfate, iron sulfide, strontium sulfate and barium sulfate are the most common scales in the oil and gas industry 5. Scale formation in oil and gas fields is a costly problem due mainly to causing lower oil and gas production and requiring frequent down-hole equipment replacement, re-perforation of productive intervals, re-drilling of plugged oil wells and other remedial workovers needed to avoid its consequences. Also, it is a significant cause of formation damage in both injection and production wells 3, 4. Scale causes blockage of wellbore perforations, pipelines and valves, leading to equipment wear, corrosion and flow restriction, reducing oil and gas output 2. Scale deposits around the wellbore clog the porous formation medium, making the formation impervious to fluids. Scale formation is a critical operational issue in surface and subsurface oil and gas equipment as it could occur at all stages during oil and gas production. Scale is a common term used in the oil and gas industry to describe solid deposits that grow over time, blocking and hindering fluid flow 1. The single step dissolution process showed its effectiveness and could potentially save significant pumping time if implemented in operation. Both 7-pH and 10.5-pH dissolvers showed high stability at high temperature and minimum corrosion rates. The reaction product has been characterized and showed it is not corrosive. The 10.5-pH dissolver was effective in most of the cases and provided highest dissolution efficiency. 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% CaSO 4 dissolution. A reaction product (K 2SO 4) was obtained in most of the tests with different quantities and was soluble in both water and HCl. 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. 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 (K 2CO 3), temperature impact and agitation effect. The CaSO 4 scale was converted to calcium carbonate (CaCO 3) and potassium sulfate (K 2SO 4) using a conversion agent, potassium carbonate (K 2CO 3), at a high temperature (200 ☏) and under various pH conditions. In this study, a single-step method utilizing potassium carbonate and tetrapotassium ethylenediaminetetraacetate (K4-EDTA) at high temperature (200 ☏) has been used to remove CaSO 4 scale. 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. Calcium sulfate (CaSO 4) 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.
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