Fluid loss control additive

1. A fluid loss control additive comprising:

a copolymer comprising 2-acrylamido-2-methylpropane sulfonic acid monomer units and acryloylmorpholine monomer units; and

a graft copolymer comprising a humate and, grafted onto the humate, a side-chain polymer comprising:

acrylamide monomer units;

acryloylmorpholine monomer units;

acrylic acid monomer units; and

2-acrylamido-2-methylpropane sulfonic acid monomer units;

wherein:

the acrylamide monomer units comprise about 10% to about 40% of a total number of monomer units of the side-chain polymer;

the acryloylmorpholine monomer units comprise about 5% to about 35% of a total number of monomer units of the side-chain polymer;

the acrylic acid monomer units comprise about 10% to about 40% of a total number of monomer units of the side-chain polymer; and

the 2-acrylamido-2-methylpropane sulfonic acid monomer units comprise about 20% to about 75% of a total number of monomer units of the side-chain polymer.

2. The fluid loss control additive of claim 1 , wherein:

the 2-acrylamido-2-methylpropane sulfonic acid monomer units comprise about 10% to about 90% of a total number of monomer units of the copolymer; and

the acryloylmorpholine monomer units comprise about 10% to about 90% of a total number of monomer units of the copolymer.

3. The fluid loss control additive of claim 1 , wherein:

the 2-acrylamido-2-methylpropane sulfonic acid monomer units comprise about 40% to about 80% of a total number of monomer units of the copolymer; and

the acryloylmorpholine monomer units comprise about 20% to about 60% of a total number of monomer units of the copolymer.

4. The fluid loss control additive of claim 1 , wherein the humate comprises about 1 wt % to about 20 wt % of the graft copolymer.

5. The fluid loss control additive of claim 1 , wherein the copolymer and the graft copolymer are present in the additive in a weight ratio of about 100:1 to about 1:100.

6. The fluid loss control additive of claim 1 , wherein the copolymer and the graft copolymer are present in the additive in a weight ratio of about 4:1 to about 1:4.

7. The fluid loss control additive of claim 1 , comprising:

about 20 wt % to about 80 wt % of the copolymer; and

about 20 wt % to about 80 wt % of the graft copolymer.

8. The fluid loss control additive of claim 1 , wherein the copolymer and the graft copolymer are present in a combined amount of at least about 80 wt % of the additive.

9. A slurry, comprising:

water;

a cement;

a copolymer of 2-acrylamido-2-methylpropane sulfonic acid monomer units and acryloylmorpholine monomer units; and

a graft copolymer comprising a humate and, grafted onto the humate, a side-chain polymer comprising:

acrylamide monomer units;

acryloylmorpholine monomer units;

acrylic acid monomer units; and

2-acrylamido-2-methylpropane sulfonic acid monomer units;

wherein:

the acrylamide monomer units comprise about 10% to about 40% of a total number of monomer units of the side-chain polymer;

the acryloylmorpholine monomer units comprise about 5% to about 35% of a total number of monomer units of the side-chain polymer;

the acrylic acid monomer units comprise about 10% to about 40% of a total number of monomer units of the side-chain polymer; and

the 2-acrylamido-2-methylpropane sulfonic acid monomer units comprise about 20% to about 75% of a total number of monomer units of the side-chain polymer.

10. The slurry of claim 9 , wherein the cement comprises a Portland cement.

11. The slurry of claim 9 , wherein the cement comprises a Portland cement and a slag cement.

12. The slurry of claim 9 , wherein:

a weight of the copolymer present in the slurry is about 0.05% to about 10% of a weight of the cement present in the slurry; and

a weight of the graft copolymer present in the slurry is about 0.05% to about 10% of the weight of the cement present in the slurry.

13. The slurry of claim 9 , wherein:

a weight of the copolymer present in the slurry is about 0.1% to about 5% of a weight of the cement present in the slurry; and

a weight of the graft copolymer present in the slurry is about 0.1% to about 5% of the weight of the cement present in the slurry.

14. The slurry of claim 9 , further comprising an American Petroleum Institute (API) Class G cement.

15. The slurry of claim 13 , wherein a weight of the API Class G cement present in the slurry is about 0.1% to about 35% of a weight of the cement present in the slurry.

16. The slurry of claim 13 , wherein a weight of the API Class G cement present in the slurry is about 0.5% to about 10% of a weight of the cement present in the slurry.

17. The slurry of claim 9 , further comprising at least one retarder, wherein a total weight of the at least one retarder is about 0.1% to about 35% of a weight of the cement present in the slurry.

18. The slurry of claim 9 , further comprising:

zinc oxide;

diethylenetriamine penta(methylene phosphonic acid); and

a second copolymer comprising 2-acrylamido-2-methylpropane sulfonic acid monomer units and acrylic acid monomer units;

wherein:

a weight of the zinc oxide present in the slurry is about 0.1% to about 1% of a weight of the cement present in the slurry;

a weight of the diethylenetriamine penta(methylene phosphonic acid) present in the slurry is about 0.1% to about 1% of a weight of the cement present in the slurry; and

a weight of the second copolymer present in the slurry is about 0.1% to about 1% of the weight of the cement present in the slurry.

19. The slurry of claim 9 , further comprising at least one superplasticizer, wherein a total weight of the at least one superplasticizer present in the slurry is about 0.1% to about 5% of a weight of the cement present in the slurry.

20. The slurry of claim 9 , further comprising a polycarboxylate ether, wherein a weight of the polycarboxylate ether present in the slurry is about 0.1% to about 1.5% of a weight of the cement present in the slurry.

21. The slurry of claim 9 , further comprising a defoamer, wherein a total weight of the defoamer is about 0.001% to about 0.2% of a weight of the cement present in the slurry.

22. The slurry of claim 9 , wherein the cement and the water are present in the slurry in a weight ratio of about 3:1 to about 1:1.

23. The slurry of claim 9 , further comprising an API Class G cement, wherein:

the cement comprises a Portland cement;

a weight of the copolymer present in the slurry is about 0.05% to about 10% of a weight of the cement present in the slurry;

a weight of the graft copolymer present in the slurry is about 0.05% to about 10% of the weight of the cement present in the slurry;

a weight of the API Class G cement present in the slurry is about 0.1% to about 35% of the weight of the cement present in the slurry; and

the cement and the water are present in the slurry in a weight ratio of about 3:1 to about 1:1.

24. The slurry of claim 9 , comprising a fluid loss of about 0 mL per 30 min. to about 150 mL per 30 min., measured at an operating temperature of about 180° F. according to API Recommended Practice 10B-2.

25. The slurry of claim 9 , comprising a fluid loss of about 0 mL per 30 min to about 50 mL per 30 min., measured at an operating temperature of about 180° F. according to API Recommended Practice 10B-2.

26. The slurry of claim 9 , comprising a density of about 10 lbs./gal. to about 17 lbs./gal.

27. A method of controlling fluid loss of a cement slurry, the method comprising mixing, in any order:

water;

a cement;

a copolymer comprising 2-acrylamido-2-methylpropane sulfonic acid monomer units and acryloylmorpholine monomer units; and

a graft copolymer comprising a humate and, grafted onto the humate, a side-chain polymer comprising:

acrylamide monomer units;

acryloylmorpholine monomer units;

acrylic acid monomer units; and

2-acrylamido-2-methylpropane sulfonic acid monomer units;

wherein:

the acrylamide monomer units comprise about 10% to about 40% of a total number of monomer units of the side-chain polymer;

the acryloylmorpholine monomer units comprise about 5% to about 35% of a total number of monomer units of the side-chain polymer;

the acrylic acid monomer units comprise about 10% to about 40% of a total number of monomer units of the side-chain polymer; and

the 2-acrylamido-2-methylpropane sulfonic acid monomer units comprise about 20% to about 75% of a total number of monomer units of the side-chain polymer.

28. The method of claim 27 , comprising mixing a drilling fluid comprising water with, in any order, the cement, the copolymer, and the graft copolymer.