Method to reduce the water loss in slurries or solutions used in oil field and gas field operations

1. A method for reducing water loss in aqueous slurries of particulate solids and/or in aqueous solutions for oil field and/or gas field operations, said process comprising the steps of:

adding to the said slurry or to said solution a copolymer having a high molecular weight characterized by a K value of at least 300, determined as 0.1 weight % copolymer concentration in deionized water, said copolymer comprising

(i) 0.1 to 20 weight % of structural units of formula (I),

and

(ii) 5 to 90 weight % of structural units of formula (II),

and

(iii) 5 to 75 weight % of structural units of formula (III)

and

(iv) up to 20 weight % of structural units of formula (IV), said structural unit of formula (IV) is different from structural units of the formula (II),

wherein

B is a two-valent organic bridge group, and if structural units of formula (IV) are present, B can also be a covalent bond forming a direct linkage,

R9 is hydrogen or C 1 -C 6 -alkyl,

R10 is hydrogen, a cation of an alkaline metal, of an earth alkaline metal, and/or of ammonia,

wherein the sum of the structural units of formulae (I), (I), (III), and (IV) if present, amounts to 100 weight % of the total mass of the copolymer, and

R1, R4 and R6 are independently of one another hydrogen or C 1 -C 6 -alkyl,

R2, R3 and R5 are independently of one another hydrogen, a cation of an alkaline metal, of an earth alkaline metal, of ammonia and/or of an organic amine,

R7 and R8 are independently of one another hydrogen or C 1 -C 6 -alkyl,

A is a covalent C—P bond or a two-valent organic bridge group, and

B is a two-valent organic bridge group,

with the proviso, that the copolymer is added to said slurry or to said solution in the absence of any glycol and/or glycol-ether compounds.

2. The method according to claim 1 , wherein R1, R4 and R6 are independently of one another hydrogen or methyl and R2, R3 and R5 are independently of one another hydrogen or a cation of an alkali metal, of an earth alkaline metal, or of ammonia and R7 and R8 are independently of one another hydrogen, methyl or ethyl, preferably hydrogen.

3. The method of claim 1 , wherein A is a C—P covalent bond or a —C n H 2n group with n being an integer between 1 and 6, and B is a —CO—NH—C m H 2m — group with m being an integer between 1 and 6.

4. The method of claim 1 , wherein R9 is hydrogen or methyl.

5. The method according to claim 1 , wherein the copolymer comprises

(i) 40 to 80 weight % of structural units of formula (II) and its alkali salts and/or ammonium salts,

(ii) 1 to 10 weight % of structural units of formula (I) and its alkali salts and/or ammonium salts and

(iii) 10 to 59 weight % of structural units of formula (III).

6. The method according to claim 1 , wherein the copolymer is added to aqueous suspensions of particulate solids, cement slurries, gypsum slurries, mortars, or drilling muds or wherein the copolymer is added to aqueous solutions, including saline solutions.

7. The method according to claim 6 , wherein concentration of the copolymer added to the aqueous suspensions of particulate solids is between 0.1 to 4 weight %.

8. The method according to claim 7 , wherein the solids content of the final aqueous suspension of particulate solids is between 2 and 75 weight %.

9. The method according to claim 1 , wherein the concentration of the copolymer added to the aqueous solutions is between 0.2 and 8 weight %.

10. The method according to claim 1 , wherein to the aqueous solutions comprising the copolymer with structural units of formulae (I), (II) and (III), and (IV), adding CaCl 2 and/or CaBr 2 to increase the density of said aqueous solution above 1 g/ml.

11. The method of claim 3 wherein n is 1.

12. The method of claim 3 wherein m is between 2 and 4.

13. The method of claim 3 wherein B is —CO—NH—C(CH 3 ) 2 —CH 2 —.

14. The method of claim 10 wherein the density of said aqueous solution is in a range of 1.4 to 1.81 g/ml.