Table 4 API recommended range of drilling fluids properties. API specification for mud (American Society of Mechanical Engineers, 2005)

Plastic viscosity (PV)

cp

 < 35

Apparent viscosity (AV)

cp

–

Yield point (YP)

lb/100ft²

15–25

Initial gel-strength (initial GS)

lb/100ft²

6–10

10-min gel strength (10-min GS)

lb/100ft²

8–12

pH

-

8–10

Filtrates loss (FL)

ml

 < 4

Filter cake thickness (FCT)

mm

 < 2

Electrical stability (ES)

volts

 > 400