Total Flow Area (TFA) is summation of nozzle areas which fluid can pass through a bit. When you consider about the TFA, you need to count all nozzles that you have in a bit or a reamer.
Basically, you can determine flow area with a simple circle area formula.
Flow Area = (π × D2) ÷ 4
Where;
Area in square inch
π is a constant which approximately equates to 3.14159.
D is diameter in inch
Let’s make it easier for our life. Normally, a diameter of nozzle is reported in xx/32 inch. For example, a bit has 3 nozzles and each one of them has size of 20/32 inch.
The formula above can be simplified like this.
Oilfield Unit
Flow Area = N2 ÷ 1303.8
Where;
Flow Area for each nozzle in square inch
N is nozzle size in number/32 inch.
In order to find the total flow area of each bit or reamer, you must add all area of each nozzle.
Example
The bit that has a total of 5 nozzles. Three nozzles have a diameter of 10/32 inch and other 2 nozzles are 12/32 inch diameter.
Determine the total flow area (TFA) of the bit.
By the definition, you must sum every nozzle together in order to get the TFA; therefore, you can apply the formula above into this form.
Total Flow Area = (102 + 102 + 102 + 122 + 122 )÷ 1303.8
Total flow area = 0.451 square inch
Metric Unit
Flow Area = N2 × π ÷ 4
Where;
Flow Area for each nozzle in square millimeter
N is nozzle size in millimeter .
Example
The bit that has a total of 5 nozzles. Three nozzles have a diameter of 7.94 mm and other 2 nozzles are 9.53 mm diameter.
Determine the total flow area (TFA) of the bit.
Total Flow Area = (7.942 + 7.942 + 7.942 + 9.532 + 9.53 2 ) × π ÷ 4
Total flow area = 291 square mm
Download Excel Spreadsheet for Total Flow Area Table in 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.
