GB1293440A - Improvements in or relating to scale removal solvents and processes - Google Patents

Abstract

1293440 Scale-removing composition F J QUATTRINI 8 Sept 1970 42893/70 Heading C7E [Also in Division E1] An aqueous composition for dissolving scale deposits comprises a partially neutralised amino polyacetic acid and an alkali metal or ammonium carbonate and/or bicarbonate and has pH 6À5 to 9À5. Mono- or poly-amino polyacetic acids may be used, e.g. EDTA,diethylene triaminepeutaacetic acid, N-hydroxyethyl amino diacetic acid or nitrilo-triacetic acid, preferred concentrations being 10-18 wt%. Partial neutralisation is achieved by adding, to pH 6À5 to 9À5, an inorganic alkali, typically 3-10% of NaOH, KOH, or NH 4 OH, or 2-12% of a hydroxyamine, e.g. mono, di, or triethanolamine, monoisopropanolamine, mixed isomers of isopropanolamine, morpholine, N- amino ethyl morpholine, or short-chain derivatives of these. The carbonate is preferably NH 4 , Na, or K carbonate or bicarbonate in amount 5-15%. The composition may optionally contain 1-6% of an acidulating and reaction-promoting agent such as HCHO, glyoxaldehyde, pyruvic aldehyde, acetaldehyde, propion-aldehyde, ammonium hydroxyacetate and/or ammonium sulphamate; 5-10% solubilising agent, e.g. urea, and 1-3% surfactant, e.g. polyethylene glycol or sodium alkyl or aryl sulphonate. The composition is used e.g. at 50-60‹F to remove scale such as CaSO 4 or sulphates or carbonates of Ca, Mg, or Ba from an oil well, e.g. casing, tubing, and pumps. The composition, applied under pressure, will also dissolve such materials from a rock matrix, thereby establishing new porosity and flow channels within a well.