Buoyancy Factor is the factor that is used to compensate loss of weight due to immersion in drilling fluid.
Before explaining any further, I will explain you about the basic concept of Buoyancy. Buoyancy is the upward force that keeps things afloat. The net upward buoyancy force equals to the amount of the weight of fluid displaced by the body volume. This force will make objects lighter when it immerses in fluid. For example, we feel ourselves lighter when we are in swimming pool because this is the effect of buoyancy.
In drilling operation, we need to know how much weight of string of drill pipe, completion string, etc in drilling fluid. Therefore, Buoyancy Factor is value that we need to know and be able to calculate this value. Please follow the formulas below to calculate Buoyancy Factor in different mud weight units, ppg and lb/ft3.
Buoyancy Factor using mud weight in ppg
Buoyancy Factor (BF) = (65.5 – mud weight in ppg) ÷65.5
Example: Determine the buoyancy factor for a 13.0 ppg fluid:
BF = (65.5 – 13.0) ÷ 65.5
BF = 0.8015
Buoyancy Factor using mud weight in lb/ft3
Buoyancy Factor (BF) = (489 – mud weight in lb/ft3) ÷489
Example: Determine the buoyancy factor for a 100 lb/ft3 fluid:
BF = (489 – 100) ÷489
BF = 0.7955
How to use the Buoyancy Factor
In order to figure out the actual weight of drilling string in mud, the air weight of drilling string times the buoyancy factor equal to actual weight in mud, called buoyed weight.
For example , determine the string weight in 13.0 ppg mud. Air weight of string is 350 klb.
The buoyancy factor for a 13.0 ppg fluid:
BF = (65.5 – 13.0) ÷ 65.5
BF = 0.8015
The bouyed weight of drill string in 13.0 ppg mud = 350 x 0.8015 = 280.5 Klb.
Please find the Excel sheet used to calculate Buoyancy Factor
Ref book: Formulas and Calculations for drill, production and workover by Norton J. Lapeyrouse
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June 21st, 2009 at 12:09 am
[...] Buoyancy factor = (65.5 – 12.0) ÷ 65.5 = 0.817 [...]
July 14th, 2009 at 4:24 pm
Hi, during drilling process we need to know how much weight of string of drill pipe, completion string, etc in drilling fluid. Buoyancy Factor is value that we need to know and be able to calculate this value.
Regards
July 14th, 2009 at 5:11 pm
During drilling or running completion, you can see the actual weight from your weight indicator. That number is already accounted for Buoyancy factor already.