DRILLING WITH WATER-BASED MUD INCLUDING MULTIPLE CLAYS

1 . A method comprising:

rotating a drill bit against a subterranean formation, thereby cutting into the subterranean formation and forming a wellbore; and

circulating an aqueous drilling fluid through a drill string coupled to the drill bit, thereby lubricating and cooling the drill bit, wherein the aqueous drilling fluid comprises bentonite and a synthetic clay at a bentonite to synthetic clay ratio of about 5:1, the bentonite has a density of about 2,200 kilograms per cubic meter (kg/m 3 ) to about 2,800 kg/m 3 , the synthetic clay has a density of about 700 kg/m 3 to about 1,300 kg/m 3 , and the aqueous drilling fluid has a low shear yield point of about 46 pounds per 100 square feet (lb/100 ft 2 .

2 . The method of claim 1 , wherein the bentonite has a density of about 2,300 (kg/m 3 ), the synthetic clay has a density of about 1,000 kg/m 3 , and the synthetic clay has a chemical formula of Na 0.7 Si 8 Mg 5.5 Li 0.3 O 20 (OH) 4 .

3 . The method of claim 2 , wherein the aqueous drilling fluid is free of sepiolite.

4 . (canceled)

5 . The method of claim 4 , wherein the synthetic clay has an average particle diameter in a range of from about 1 nanometer (nm) to about 50 nm.

6 . The method of claim 5 , wherein the aqueous drilling fluid comprises from about 0.1 weight percent (wt. %) to about 2 wt. % bentonite.

7 . The method of claim 6 , wherein the aqueous drilling fluid comprises water and at least one of a pH modifier, a filtration control agent, a thickening agent, a clay inhibitor, or a weighting material.

8 . The method of claim 7 , wherein the aqueous drilling fluid comprises:

from about 20 wt. % to about 90 wt. % water;

from about 0.01 wt. % to about 1 wt. % soda ash;

from about 0.1 wt. % to about 2 wt. % starch;

from about 0.01 wt. % to about 1 wt. % xanthan gum;

from about 0.01 wt. % to about 1 wt. % caustic soda;

from about 0.01 wt. % to about 1 wt. % clay inhibitor; and

a balance of the weighting material.

9 . A method comprising:

flowing an aqueous drilling fluid from a surface location through a drill string and into a wellbore formed in a subterranean formation, wherein at least a portion of the drill string is disposed within the wellbore, wherein the aqueous drilling fluid comprises bentonite and synthetic clay at a bentonite to synthetic clay ratio of about 5:1, the bentonite has a density of about 2,200 kilograms per cubic meter (kg/m 3 ) to about 2,800 kg/m 3 , the synthetic clay has a density of about 700 kg/m 3 to about 1,300 kg/m 3 , and the aqueous drilling fluid has a low shear yield point of about 46 pounds per 100 square feet (lb/100 ft 2 ;

while flowing the aqueous drilling fluid, rotating a drill bit coupled to the drill string within the wellbore, thereby cutting into the subterranean formation and elongating the wellbore; and

receiving, at the surface location, the drilling fluid from the wellbore.

10 . The method of claim 9 , wherein the bentonite has a density of about 2,300 (kg/m 3 ), the synthetic clay has a density of about 1,000 kg/m 3 , and the synthetic clay has a chemical formula of Na 0.7 Si 8 Mg 5.5 Li 0.3 O 20 (OH) 4 .

11 . The method of claim 10 , wherein the aqueous drilling fluid is free of sepiolite.

12 . (canceled)

13 . The method of claim 12 , wherein the synthetic clay has an average particle diameter in a range of from about 1 nanometer (nm) to about 50 nm.

14 . The method of claim 13 , wherein the aqueous drilling fluid comprises from about 0.1 weight percent (wt. %) to about 2 wt. % bentonite.

15 . The method of claim 14 , wherein the aqueous drilling fluid comprises water and at least one of a pH modifier, a filtration control agent, a thickening agent, a clay inhibitor, or a weighting material.

16 . The method of claim 15 , wherein the aqueous drilling fluid comprises:

from about 20 wt. % to about 90 wt. % water;

from about 0.01 wt. % to about 1 wt. % soda ash;

from about 0.1 wt. % to about 2 wt. % starch;

from about 0.01 wt. % to about 1 wt. % xanthan gum;

from about 0.01 wt. % to about 1 wt. % caustic soda;

from about 0.01 wt. % to about 1 wt. % clay inhibitor; and

a balance of the weighting material.

17 . A drilling rig comprising:

a drill string assembly comprising a rotatable drill bit; and

a fluid circulation system connected to the drill string assembly, the fluid circulation system comprising:

an aqueous drilling fluid comprising bentonite and synthetic clay at a bentonite to synthetic clay ratio of about 5:1, wherein the bentonite has a density of about 2,200 kilograms per cubic meter (kg/m 3 ) to about 2,800 kg/m 3 , the synthetic clay has a density of about 700 kg/m 3 to about 1,300 kg/m 3 , and the aqueous drilling fluid has a low shear yield point of about 46 pounds per 100 square feet (lb/100 ft 2 );

a drilling fluid pit holding a volume of the aqueous drilling fluid; and

a pump configured to flow the drilling fluid from the drilling fluid pit to the drill string assembly while the rotatable drill bit rotates.

18 . The drilling rig of claim 17 , wherein the aqueous drilling fluid is free of sepiolite and comprises:

from about 20 weight percent (wt. %) to about 90 wt. % water;

from about 0.1 wt. % to about 2 wt. % bentonite;

the synthetic clay, such that the bentonite to synthetic clay ratio is about 5:1;

from about 0.01 wt. % to about 1 wt. % soda ash;

from about 0.1 wt. % to about 2 wt. % starch;

from about 0.01 wt. % to about 1 wt. % xanthan gum;

from about 0.01 wt. % to about 1 wt. % caustic soda;

from about 0.01 wt. % to about 1 wt. % clay inhibitor; and

a balance of weighting material.

19 . (canceled)

20 . (canceled)