Method and composition for cleaning a well bore prior to cementing

1. A spacer fluid composition for cleaning a section of a well bore prior to cementing which comprises at least one alkyl ether citrate of general formulae I, II and/or III:

wherein x is 1-20; m is 1-50; and n is 0-10, and optionally at least one alcohol ethoxylate of general formula IV:

CH 3 (CH 2 )x(C 2 H 4 O)m(C 3 H 6 O)nOH  IV

wherein x is 1-20; m is 1-50; n is 0-10; and said at least one alkyl ether citrate is employed in said spacer fluid at a concentration of from about 1 to about 3% by weight, based on 100% active.

2. The composition of claim 1 additionally comprising at least one optional component selected from weighting agents, solvents, viscosifying agents, lost circulation control agents, and mixtures thereof.

3. The composition of claim 2 wherein the viscosifying agent is welan gum, xanthan gum, a high molecular weight cellulose derivative, or a mixture thereof.

4. The composition of claim 3 wherein said high molecular weight cellulose derivative is carboxymethylcellulose (CMC), hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), or mixtures thereof.

5. The composition of claim 1 wherein said alkyl ether citrate is an heptylether citrate ethoxylate, octylether citrate ethoxylate, nonylether citrate ethoxylate, decylether citrate ethoxylate, hendecylether citrate ethoxylate, docylether citrate ethoxylate, tridecylether citrate ethoxylate, tetradecylether citrate ethoxylate, or a mixture thereof.

6. The composition of claim 1 which comprises at least one alcohol ethoxylate of general formula IV wherein the weight ratio of alkyl ether citrate to alcohol ethoxylate is in the range of from about 0.1-50.

7. The composition of claim 6 wherein said alcohol ethoxylate is linear or branched heptyl alcohol ethoxylate, octyl alcohol ethoxylate, nonyl alcohol ethoxylate, decyl alcohol ethoxylate, hendecyl alcohol ethoxylate, docyl alcohol ethoxylate, tridecyl alcohol ethoxylate, tetra alcohol ethoxylate, or a mixture thereof.

8. The composition of claim 7 wherein the weight ratio of alkyl ether citrate to alcohol ethoxylate is in the range of from about 0.5-25.

9. The composition of claim 8 wherein the weight ratio of alkyl ether citrate to alcohol ethoxylate is in the range of from about 0.5-5.

10. The composition of claim 6 wherein said combination of said at least one alkyl ether citrate and said at least one alcohol ethoxylate is employed in the spacer fluid composition at a concentration of from about 0.5% by weight to about 10% by weight based on 100% active.

11. The composition of claim 10 wherein said combination of said at least one alkyl ether citrate and said at least one alcohol ethoxylate—is employed in the spacer fluid composition at a concentration of from about 1.5 to about 3% by weight, based on 100% active.

12. A method for cleaning a section of a well bore prior to a cementing operation, said well bore having a casing suspended therein, said method comprising:

a) optionally displacing drilling fluid from the section of said borehole to be cemented, with a composition that comprises water, an effective amount of solid particles for weighting, and from about 1 to 20 vol. % of a surfactant;

b) pumping into said borehole the spacer fluid of claim 1 , under turbulent flow conditions, in an amount to effective to remove and displace substantially all of any remaining drilling fluid residue and to displace said optional first spacer fluid from the cleaned section of the borehole; and

c) optionally, pumping into said borehole a third fluid which is a water-based composition comprised of an aqueous solution of a surfactant component, wherein the amount of surfactant is about 1 to 20 vol. %, based on the total volume of said spacer fluid, and wherein said third fluid is used in an amount that will effectively displace substantially all of said second spacer fluid and leave at least the cleaned section of said borehole substantially water wet.

13. The method of claim 12 wherein said alkyl ether citrate of said spacer fluid is an heptylether citrate ethoxylate, octylether citrate ethoxylate, nonylether citrate ethoxylate, decylether citrate ethoxylate, hendecylether citrate ethoxylate, docylether citrate ethoxylate, tridecylether citrate ethoxylate, tetradecylether citrate ethoxylate, or a mixture thereof.

14. The method of claim 12 wherein said spacer fluid further comprises at least one alcohol ethoxylate which is a linear or branched heptyl alcohol ethoxylate, octyl alcohol ethoxylate, nonyl alcohol ethoxylate, decyl alcohol ethoxylate, hendecyl alcohol ethoxylate, docyl alcohol ethoxylate, tridecyl alcohol ethoxylate, tetra alcohol ethoxylate, or a mixture thereof.

15. The method of claim 14 wherein said spacer fluid comprises a combination of said at least one alkyl ether citrate and said at least one alcohol ethoxylate, and wherein said combination is employed in the spacer fluid composition at a concentration of from about 1.0% by weight to about 5% by weight based on 100% active.