Process for treating an oil well

1. A method of treating a subterranean formation, the method comprising:

forming an admixture of an emulsion (a) having an internal aqueous phase comprising a water-soluble oil or gas field chemical or an aqueous dispersion of a water-dispersible oil or gas field chemical and an external oil phase comprising a liquid hydrocarbon and an oil-soluble surfactant and a demulsifier comprising a solution of at least one surfactant dissolved in a solvent selected from the group consisting of monoethylene glycol, tetraethylene glycol, butylethylene glycol, butyldiethylene glycol, water, xylene and toluene (b) comprising a solution of a surfactant having a cloud point temperature of above 40° C.; and

injecting said admixture down a well bore into the formation.

2. A method according to claim 1 wherein the time interval between preparation of the admixture and injection of the admixture down the well bore is less than 5 hours.

3. A method according to claim 1 wherein the water-soluble or water-dispersible oil or gas field chemical is selected from the group consisting of (i) scale inhibitors, (ii) corrosion inhibitors, (iii) inhibitors of asphaltene deposition, (iv) hydrogen sulphide scavengers and (v) hydrate inhibitors.

4. A method according to claim 1 wherein the oil or gas field chemical is dissolved or dispersed in the internal aqueous phase of the emulsion in an amount in the range of from 5 to 30 percent by weight.

5. A method according to claim 1 wherein the oil-soluble surfactant of the emulsion has a hydrophilic/lipophilic balance value in the range 4 to 6.

6. A method according to claim 1 wherein the emulsion has droplets of the internal aqueous phase having average diameters of from 0.1 to 10 microns.

7. A method according to claim 1 wherein the internal aqueous phase of the emulsion amounts to from 30 to 60 percent of the total volume of the emulsion.

8. A method according to claim 1 wherein the demulsifier comprises a solution of a surfactant having a cloud point temperature of at least 60° C.

9. A method according to claim 1 wherein the cloud point temperature of the demulsifier is controlled to a value of at least 50° C. less than the formation temperature by adjusting the concentration of surfactant in the demulsifier.

10. A method according to claim 1 wherein the demulsifier comprises at least one surfactant selected from the group consisting of:

(a) polyamine salts such as polyester amines, amino methylated poly acrylamide, poly di-methyl amino propyl methacrylamide, poly dimethyl amino ethyl acrylate, poly ethylene imine, poly vinyl pyrrolidone, caprolactam-based polymers and quaternised versions thereof;

(b) multifunctional polyethers such as sulfated triglycerides;

(c) polyethers, such as copolymers of ethylene oxide and propylene oxide and the reaction products of such copolymers with diacids, diepoxides, diisocyanates, aldehydes, and diamines; and

(d) p-alkylphenol-formaldehyde resins and ethylene oxide and/or propylene oxide derivatives thereof.

11. A method according to claim 1 wherein the concentration of surfactant in the demulsifier is in the range of from 0.1 to 2 percent by weight.

12. A method of treating a subterranean formation, the method comprising:

forming an admixture of (a) an emulsion having an internal aqueous phase comprising a water-soluble oil or gas field chemical or an aqueous dispersion of a water-dispersible oil or gas field chemical and an external oil phase comprising a liquid hydrocarbon and an oil-soluble surfactant and (b) a demulsifier comprising a solution of a surfactant dissolved in a solvent selected from the group consisting of monoethylene gylcol, tetraethylene gylcol, butylethylene gylcol, butyldiethylene gylcol, water, xylene and toluene having a cloud-point temperature of at least 60° C.; and

injecting said admixture down a well bore into the formation.