This article demonstrates how to calculate Specific Gravity (SG) from different density or pressure gradient in both oilfield and metric unit.
Calculate Specific Gravity from Mud Weight In Oilfield Unit
Calculate specific gravity using mud weight in PPG
Specific Gravity (SG) = mud weight in ppg ÷ 8.33
Example:
Mud weight = 13.0 ppg
Specific Gravity (SG) = 13.0 ppg ÷ 8.33
Specific Gravity (SG)= 1.56
Calculate specific gravity using pressure gradient in psi/ft
Specific Gravity (SG) = pressure gradient in psi/ft ÷ 0.433
Example:
Pressure gradient = 0.50 psi/ft
Specific Gravity (SG) = 0.50 psi/ft ÷ 0.433
Specific Gravity (SG) = 1.15
Calculate specific gravity using mud weight in lb/ft3
Specific Gravity (SG) = mud weight in lb/ft3 ÷ 62.4
Example:
Mud weight = 90 lb/ft3
Specific Gravity (SG)= 90 lb/ft3÷ 62.4
Specific Gravity (SG) = 1.44
Calculate Specific Gravity from Mud Weight In Metric Unit
Calculate specific gravity using mud weight in kg/m3
Specific Gravity (SG) = mud weight in kg/m3÷ 1000
Example:
Mud density = 1200 kg/m3
Specific Gravity (SG) = 1200 kg/m3÷ 1000
Specific Gravity (SG)= 1.2
Calculate specific gravity using mud weight in g/cc
Specific Gravity (SG) = mud weight in g/cc÷ 1.0
Example:
Mud density = 1.2 g/cc
Specific Gravity (SG) = 1.2 g/cc÷ 1000
Specific Gravity (SG)= 1.2
Calculate specific gravity using pressure gradient in kPa/m
Specific Gravity (SG) = pressure gradient in kPa/m ÷ 9.81
Example:
Pressure gradient = 10 kPa/m
Specific Gravity (SG) = 10 kPa/m÷ 9.81
Specific Gravity (SG)= 1.02
Please also find the Excel sheet for this topic – Specific Gravity 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.
