Scale dissolution by mixtures of aminocarboxylates and hydroxides Disclosed anonymously_

摘要

Aminocarboxylates in combination with metal hydroxides were shown to exhibit good dissolving power towards scales, such as they can be found in subterranean wells or equipment used in or in relation to such wells. These wells include subterranean oil production wells, gas production wells, and geothermal wells. The scales that were found to dissolve better using the combination of an aminocarboxylate salt and a hydroxide salt are scales such as fluoride scales, sulfate scales, silicate scales, sulfide scales, carbonate scales, hydroxide scales, and oxide scales. Many of these scales are based on an alkaline earth metal cation such as barium, calcium, and/or magnesium or a metal cation such as iron, antimony, or aluminum. More particular scales are calcium carbonate, caldum fluoride, calcium sulfate, caldum oxalate, calcium silicate, caldum phosphates induding hydroxyapatite, barium sulfate, magnesium hydroxide, magnesium oxide, magnesium silicate, aluminum oxide hydroxides, alumosilicates, iron sulfides, iron hydroxides, iron silicate, ferrous carbonate, antimony and arsenic sulfides, strontium sulfate etc. Among tested aminocarboxylates, salts of MGDA, GLDA, EDTA, HEDTA and DTPA in combination with NaOH or KOH gave particularly attractive results for scales such as metal silicate scales and metal sulfide scales. For example, aqueous solutions containing both potassium or sodium salts of these aminocarboxylates and potassium or sodium hydroxide dissolved significant amounts of magnesium silicate and antimony sulfide-based scales. The amount of aminocarboxylate salt is preferably between 1 and 25 wt% in a descaling composition, more preferably between Sand 20 wt%, or between 10 and 15 wt%. The amount of NaOH or KOH is preferably between 1 and 25 wt%, more preferably between 5 and 20 wt%, or between 10 and 15 wt%on the descaling composition. The descaling composition is preferably a solution, even more an aqueous solution of the components to which further additives may be added such as corrosion inhibitors, surfactants, cos olvents, scale inhibiting and dispersing polymers etc. In embodiments it is also possible to mix two or more aminocarboxylates or salts thereof and/or two or more hydroxide salts. The process to dissolve the scale is done at a temperature of between 0 deg C and 200 deg C, even more so between 25 and 100 deg C. If the descaling composition is employed under pressure, it is in embodiments an increased pressure of between 1-200 bar. The descaling process can be done until it can be established by (visually) monitoring a well or equipment during the descaling process, inspecting them after the descaling process has been finalized, or by analyzing the outlet flow from a well that the scale has substantially dissolved. In many embodiments the descaling process takes between 10 minutes and 8 days, even more between 4 hours and 6days. In embodiments it is possible to soak the scale In the descaling composition containing the aminocarboxylate salt and the hydroxide salt, which means that the flow of such composition is decreased and in embodiments next increased.