This article describes about how to calculate and convert pressure gradient in different units. Please see simple oil field formulas shown each topic below:
1. Calculate pressure gradient in psi/ft from mud weight in ppg
Pressure gradient calculation formula:
Pressure gradient in psi/ft = mud weight in ppg x 0.052
Example:
Mud weigt = 9.0 ppg
Pressure gradient in psi/ft = 9.0 x 0.052
Pressure gradient in psi/ft = 0.468 psi/ft
2. Calculate pressure gradient in psi/ft from mud weight in lb/ft3
Pressure gradient calculation formula:
Pressure gradient in psi/ft = mud weight in lb/ft3 x 0.006944
Example:
Mud weight = 80 lb/ft3
Pressure gradient in psi/ft = 80 lb/ft3 x 0.006944
Pressure gradient = 0.55552 psi/ft
OR
Pressure gradient in psi/ft t = mud weight in lb/ft3 ÷ 144
Example:
Mud weight = 80 lb/ft3
Pressure gradient in psi/ft = 80 lb/ft3 ÷ 144
Pressure gradient = 0.55556 psi/ft
3. Calculate pressure gradient in psi/ft from specific gravity (SG)
Pressure gradient calculation formula:
Pressure gradient in psi/ft = mud weight in SG x 0.433
Example:
Fluid specific gravity = 2
Pressure gradient in psi/ft = 2.0 x 0.433
Pressure gradient = 0.866 psi/ft
4. Convert pressure gradient in psi/ft to mud weight in ppg
Pressure gradient coversion formula:
Mud weight in ppg = pressure gradient in psi/ft ÷ 0.052
Example:
Pressure gradient = 0.5 psi/ft
Mud weight in ppg = 0.5 psi/ft ÷ 0.052
Mud weight = 9.615 ppg
5. Convert pressure gradient in psi/ft to mud weight in lb/ft3
Pressure gradient coversion formula:
Mud weight in lb/ft3 = pressure gradient in psi/ft ÷ 0.006944
Example:
Pressure gradient = 0.5 psi/ft
Mud weight in lb/ft3 = 0.5 psi/ft ÷ 0.006944
Mud weight = 72 lb/ft3
6. Convert pressure gradient in psi/ft to mud weight in SG
Pressure gradient conversion formula:
SG = pressure gradient, psi/ft ÷ 0.433
Example:
Pressure gradient =0.5 psi/ft
SG = 0.5 psi/ft ÷ 0.433
SG = 1.1547
Please find the Excel sheet in the following link: Pressure Gradient Calculation Sheet
Ref books: Lapeyrouse, N.J., 2002. Formulas and calculations for drilling, production and workover, Boston: Gulf Professional publishing.
Bourgoyne, A.J.T., Chenevert , M.E. & Millheim, K.K., 1986. SPE Textbook Series, Volume 2: Applied Drilling Engineering, Society of Petroleum Engineers.
Mitchell, R.F., Miska, S. & Aadny, B.S., 2011. Fundamentals of drilling engineering, Richardson, TX: Society of Petroleum Engineers.
