Calculate Pressure Gradient and Convert Pressure Gradient

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/ft
3 = 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.

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