Which psi/ft gradient is used for freshwater calculations in petroleum contexts?

• A. 0.433 psi/ft
• B. 0.465 psi/ft
• C. 0.5 psi/ft
• D. 0.4 psi/ft

Answer: (A)

Hydrostatic pressure grows with depth in a liquid, and the rate depends on the liquid’s density. For freshwater, the density is about 62.4 pounds per cubic foot. To convert that to a pressure gradient in psi per foot, divide by 144 (the number of square inches in a square foot): 62.4 / 144 ≈ 0.433. That 0.433 psi per foot is the standard freshwater gradient used in petroleum calculations to estimate the pressure contribution of a freshwater column and to size mud weights or predict wellbore pressures at depth.

Other values would imply different fluid densities: 0.4 psi/ft would correspond to a lighter fluid, and 0.465 psi/ft to a denser brine or seawater; 0.5 psi/ft would require an even heavier fluid. Since the context specifies freshwater, 0.433 psi/ft is the appropriate gradient.