**Buoyancy Factor** is the factor that is used to compensate loss of weight due to immersion in drilling fluid.

Before explaining any further, we 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/ft^{3}.

**Buoyancy Factor In Oilfield Unit**

## Buoyancy Factor using mud weight in ppg

Buoyancy Factor (BF) = (65.5 – mud weight in ppg) ÷65.5

Note:65.5 ppg is density of steel.

**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/ft

^{3}

= (489 – mud weight in lb/ftBuoyancy Factor (BF)^{3}) ÷489

Note:489 lb/ft^{3}is density of steel.

**Example:** Determine the buoyancy factor for a 100 lb/ft^{3} fluid:

BF = (489 – 100) ÷489

BF = 0.7955

**Buoyancy Factor In Metric Unit**

## Buoyancy Factor using mud weight in kg/l

Buoyancy Factor (BF) = (7.85 – mud weight in kg/l) ÷7.85

Note:7.85 kg/l is density of steel.

**Example:** Determine the buoyancy factor for a 1.1 kg/l fluid:

BF = (7.85 – 1.1) ÷7.85

BF = 0.860

**Buoyancy Factor Table**

This table demonstrates buoyancy factor at different mud density

**How to use the Buoyancy Factor to determine buoyed weight **

To determine the weight of the drill string in drilling fluid (often called buoyed weight), we multiply the air weight of the drill string by the buoyancy factor. The buoyancy factor accounts for the weight reduction caused by the buoyant force of the drilling fluid.

Buoyed weight of drill string = String weight in the air × Buoyancy Factor

**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

**Buoyed weight of drill string = String weight in the air × Buoyancy Factor**

The buoyed weight of drill string in 13.0 ppg mud = 350 x 0.8015 = 280.5 Klb.

**Download Excel Spreadsheet for Buoyancy Factor Calculation both Oilfield and Metric Unit**

**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.

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

During drilling or running completion, you can see the actual weight from your weight indicator. That number is already accounted for Buoyancy factor already.

please i need write up on evaluation of drilling bit performance

Could you give me more details?

It is hard to locate knowledgeable folks on this subject, but you sound like you know what you are talking about! Thanks 537099

what happens if my well is completed with a 12.1 ppg completion fluid, i then go on to displace tubing fluid to 10.3 ppg. how do i find out the wet weight of the tubing string ? displacing of tubing fluid occurs before packer has set.

Your weight showing in the weight indicator will slightly increase because of reduction of density. In order to get the weight in the completion fluid, you determine the new buoyancy factor using 10.3 ppg and multiply by string weight.

Regards,

Shyne.

Is there a difference between weight of the drill string and weight of the drill string in air? Thank you!

Rinat,

Yes. Buoyed weight of drill string = String weight in the air x Buoyancy Factor

How do you calculate the bouyoncy force on the cutting of weight 8.33 ppg and the volume of mud is 3 in3 with a weight of 11ppg

Leon,

The cutting weight in your example is too low. It will float in the drilling mud.

Regards,

Shyne

What is the 65,5 on the formula for bouyancy fator?

65.5 ppg is metal density.

How the buyouancy factor affect the string Wt if the string is stinged into packer?

Mero,

The buoyancy factor still has the same effect since the string is submersed into fluid.

There are US and UK types of pounds per gallon density. Which one can be used in buoyancy factor calculation?

Thanks

US gallon is used for this calculation.

why is the buoyant weight of drill string important?

Does it play a role in the load provided/rotary motion provided.

Very Important Note. This formula for unplugged pipe at the bottom.

Thanks for the information, good job