Dissolving barium sulfate scale with aqueous solutions of salts of phosphomethyl and amino-substituted macrocyclic polyethers

A process for dissolving solid barium sulfate in or around a well in a location into which fluid can be flowed, which process comprises:

• flowing into said well and into contact with the barium sulfate an aqueous solution consisting essentially of water, a phosphomethyl and amino-substituted macrocyclic polyether and sufficient dissolved alkaline, inorganic, alkali metal or ammonium compound to provide a pH of at least about 8;
• and,
• using as said polyether a compound of the formula ##STR10## wherein each A.sup.1, which may be the same or different, represents a hydrocarbon radical of up to 12 carbon atoms and each D, which may be the same or different, represents an oxygen or sulphur atom or a hydrocarbon radical having up to 6 carbon atoms or a group N-R, representing a hydrogen atom or a hydrocarbon radical having up to 12 carbon atoms, a hydrocarbon sulphonyl radical having up to 12 carbon atoms, an alkoxycarbonylmethylene radical having up to 4 carbon atoms or a carboxymethylene radical, at least two of said D members representing an oxygen or a sulphur atom or a group N-R, and each R.sup.1, which may be the same or different, represents a hydrogen atom, an alkyl group having up to 6 carbon atoms or a carboxy group, m and n are whole numbers from 0 to 5 inclusive and Z represents a group ##STR11## wherein y is 0 or 1 and R.sup.2 and R.sup.3, which may be the same or different, represent a hydrogen atom or an alkyl group or a lithium, sodium, potassium or ammonium ion.