Method for stimulation of oil and gas wells

A method for the removal of scale from the interior of producing oil and gas wells comprising the steps of:

• (a) preparing a first mixture of an alkyl or aralkyl polyoxylene phosphate ester and a mutual solvent obtained by blending of a water soluble alcohol selected from the group consisting of methanol, ethanol, propanol and isopropanol, and an aromatic hydrocarbon, the phosphate ester having the formula ##STR7## wherein:
• R.sub.1 represents an alkyl radical having 10 to 18 carbon atoms;
• R.sub.2 represents an alkyl of about 5 to 27 carbon atoms, cycloalkyl, and radicals derived from mineral oils containing alkyl, cycloalkyl and mixed alkylcycloalkyl radicals having from about 12 to 27 carbon atoms;
• R.sub.3 and R.sub.4 represent hydrogen, alkyl having from about 1 to 22 carbon atoms, cycloalkyl, and radicals derived from mineral oils containing alkyl, cycloalkyl and mixed alkylcycloalkyl radicals having from about 12 to 27 carbon atoms;
• A represents the residue of ethylene oxide, ethylene oxide and tetrahydrofuran, or mixed lower alkylene oxides selected from the group consisting of ethylene oxide, propylene oxide, and butylene oxide alone or including tetrahydrofuran;
• and wherein the total molecular weight of the ester is about 500 to about 1,500, and A is heteric or block in molecular configuration;
• and wherein
• the degree of oxyalkylation is represented by n;
• x and y are 1 or 2;
• the sum of x and y is 3;
• z is an integer from 0 to 5;
• and
• X is hydrogen or a monovalent cation selected from the group consisting of an alkali metals;
• alkyl amines and ammonium;
• (b) preparing a second mixture by admixing a mineral acid to said first mixture to form a micellar emulsion thereof wherein the acid is present in a scale deposit effective dissolving amount and the phosphorate ester is present in an amount sufficient to maintain the acid and mutual solvent in said micellar emulsion state;
• (c) introducing the second mixture to a well;
• (d) retaining the mixture in the well for a period of time sufficient to allow the acid to solubilize the mineral deposits therein;
• and
• (e) removing the mixture and solubilized mineral deposits from the well interior.