Calculation of the buoyancy factor and its application

The buoyancy factor is the factor used to compensate for weight loss due to immersion in the drilling fluid.

Before further explaining, it is very important to explain the basic concept of Buoyancy. Buoyancy is the upward force that keeps things afloat. The net upward buoyant force is equal to the amount of the weight of the fluid displaced by the volume of the body. This force will make objects lighter when immersed in a fluid. We instantly feel lighter when we are in a pool because this is the Buoyancy effect.

How to Calculate Buoyancy Factor.

The formulas below demonstrate how to determine this factor.

Buoyancy Factor (BF) = (65.5 – mud weight density in pounds per gallon (ppg)) ÷ 65.5

For example, if the weight of the drilling fluid is 13.0 pounds per gallon (ppg), based on the equation above, the factor can be calculated by simply entering the density of the mud weight into the equation.

FB = (65.5 – 13.0) ÷ 65.5

BF = 0.8015

How to use the buoyancy factor.

To calculate the true weight of the drillstring in the mud, the weight of the drillstring air multiplied by the buoyancy factor equals the true weight of the drillstring, called the buoyant weight, in the drilling fluid. The simple equation shows the relationship of the actual weight in the drilling fluid.

Actual Weight = Air Weight of Drill String x BF

If the weight in air of a drill string is 350 kilo pounds (Klb), we can use this relationship to determine the weight of the string in 13.0 ppg of drilling fluid. The floating weight of the drill string in 13.0 ppg mud equals 350 x 0.8015 (280.5 Klb).

According to the calculation, when a drill string is submerged in the drilling fluid, its weight decreases by almost 20%. Therefore, it is very important that all personnel working on drilling sites be able to calculate the buoyancy factor to find out how the weight of the mud affects the total weight of the string in a well.