STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

Drilling Muds and Completion Fluids 671
Tabk 4-48
Seawater Composition
Concentration
Component PPm ePm
Sodium 10440 454.0
Potassium 375 9.6
Magnesium 1270 104.6
Calcium 410 20.4
Chloride 18970 534.0
Sulfate 2720 57.8
Figure 4-112. Approximate solids range in seawater muds [24]. (Courtesy M-/
Drilling Fluids.)
solids in seawater muds [24]. The pH control is quite important, and pH should
be maintained between 9 and 10. If the pH increases above 10, the magnesium
will begin to precipitate. Caustic soda is used to control pH. Filtrate alkalinity
P, should be maintained at approximately 1.5 with caustic soda. Mud alkalinity
Pm should be about 3.0 to 3.5; it is controlled with lime. If P, is too low, the gel
strength increases; if Pm is too low, mud aeration occurs; if P, is too high, mud
viscosity decreases. Filtration is controlled by addition of bentonite.
Saturated Saltwater Muds
The liquid phase of saturated saltwater muds is saturated with sodium
chloride. Saturated saltwater muds are most frequently used as workover fluids
or for drilling salt formations. These muds prevent solution cavities in the salt
formations, making it unnecessary to set casing above the salt beds. If the salt
formation is too close to the surface, a saturated saltwater mud may be mixed
in the surface system as the spud mud. If the salt bed is deep, freshwater mud
is converted to a saturated salt water mud.
Saturated saltwater muds can be weighted to more than 19 Ib/gal. Saturated
saltwater muds conditioned with organic colloids to control filtration can be