Environmental friendly well treatment fluids comprising an ester

1. A well treatment fluid comprising

(i) an ester obtainable by reacting

(a) a polycarboxylic acid with

(b) a hydroxy monocarboxylic acid; and

(ii) water and/or an organic phase

wherein the well treatment fluid is an emulsion and said hydroxy monocarboxylic acid (b) is a C12 to C36 hydroxy monocarboxylic acid.

2. The well treatment fluid according to claim 1 , wherein the organic phase comprises one or more compound selected from the group consisting of

(1) a carboxylic acid ester of formula: R′—COO—R″ (I);

where R′ is a saturated or unsaturated, linear or branched C5 to C23 alkyl group and R″ is a C1 to C22 alkyl group, which may be saturated or unsaturated, linear or branched;

(2) a linear or branched C8 to C30 olefin;

(3) a water-insoluble, symmetrical or nonsymmetrical ether of a monohydric alcohol;

(4) a water-insoluble alcohol of formula: R′″—OH (II), where R′″ is a saturated, unsaturated, linear or branched C8 to C24 alkyl group;

(5) a carbonic acid diester;

(6) a paraffin;

(7) an acetal;

(8) an α-olefin, an internal olefin, a poly-α-olefin, or combinations thereof; and

(9) diesel fuel.

3. The well treatment fluid according to claim 1 , wherein said polycarboxylic acid (a) is a dicarboxylic acid.

4. The well treatment fluid according to claim 1 , wherein said polycarboxylic acid (a) is a branched or unbranched, saturated or unsaturated polycarboxylic acid.

5. The well treatment fluid according to claim 1 , wherein said polycarboxylic acid (a) is a C4 to C56 polycarboxylic acid and more preferably a C8 to C36 polycarboxylic acid.

6. The well treatment fluid according to claim 1 , wherein said polycarboxylic acid (a) is a dicarboxylic acid having the following general structure:

wherein n is between 1 and 36 and wherein n preferably is between 3 and 18, or a C6-C40 dimer acid.

7. The well treatment fluid according to claim 1 , wherein said polycarboxylic acid (a) is selected from the group consisting of succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, 3,3-dimethylglutaric acid, terephthalic acid, isophthalic acid, cyclocarboxypropyloleicacid, naphthalenedicarboxylic acid, C6-dimer acid, C7-dimer acid, C8-dimer acid, C9-dimer acid, C10-dimer acid, C11-dimer acid, C12-dimer acid, C13-dimer acid, C14-dimer acid, C15-dimer acid, C16-dimer acid, C17-dimer acid, C18-dimer acid, C19-dimer acid, C20-dimer acid, C21-dimer acid, C22-dimer acid, C23-dimer acid, C24-dimer acid, C25-dimer acid, C26-dimer acid, C27-dimer acid, C28-dimer acid, C29-dimer acid, C30-dimer acid, C31-dimer acid, C32-dimer acid, C33-dimer acid, C34-dimer acid, C35-dimer acid, C36-dimer acid, C37-dimer acid, C38-dimer acid, C39-dimer acid, C40-dimer acid, and wherein said polycarboxylic acid (a) is most preferably azelaic acid or C21-dimer acid.

8. The well treatment fluid according to claim 1 , wherein said hydroxy monocarboxylic acid (b) is a branched, unbranched, saturated or unsaturated hydroxy monocarboxylic acid.

9. The well treatment fluid according to claim 8 , wherein said unsaturated hydroxy monocarboxylic acid (b) is selected from the group consisting of a hydroxy omega-3 fatty acid, a hydroxy omega-6 fatty acid, a hydroxy omega-7 fatty acid and a hydroxy omega-9 fatty acid.

10. The well treatment fluid according to claim 9 , wherein said hydroxy omega-9 fatty acid is selected from the group consisting of hydroxy-oleic acid, hydroxy elaidic acid, hydroxy gondoic acid, hydroxy mead acid, hydroxy erucic acid and hydroxy nervonic acid.

11. The well treatment fluid according to claim 1 , wherein said hydroxy monocarboxylic acid (b) is an aliphatic monohydroxy monocarboxylic acid.

12. The well treatment fluid according to claim 11 , wherein said hydroxy monocarboxylic acid (b) is ricinoleic acid or hydroxy stearic acid.

13. The well treatment fluid according to claim 1 , wherein said hydroxy monocarboxylic acid (b) is an unsaturated aliphatic monohydroxy monocarboxylic acid.

14. The well treatment fluid according to claim 1 , wherein said ester is azelaic ricinoleate.

15. The well treatment fluid according to claim 1 , wherein said ester has an aerobic degradability of at least 30% after 28 days in seawater according to the Marine Bodis test as defined in ISO TC/147/SC5/WG4, N 141.