Friday, October 5, 2012

Oil Drilling Reference Formula

How to calculate Bit Nozzle
Total Flow Area (TFA) = N^2/1303.8.

Where;
Area = In Square Inch
N = Nozzle size in number/32 inch.

Example: There are 3 bit nozzles where 1 nozzle have a diameter 10/32 inch and the other 2 nozzles are 8/32 inch diameter. So.

Total Flow Area = (10^2 + 8^2 + 8^2) / 1303.8 = 0.175 inch square.



How to calculate
Pipe/Casing Displacement in bbl/ft = (OD inch^2 - ID inch^2) / 1029.4

Where;
OD = is outside diameter of pipe/casing in inch
ID = is inside diameter of pipe/casing in inch

Example: Determine pipe displacement in bbl/ft of 9 1/2 casing 40 ppf, OD = 9.500 inch, ID = 8.500 inch

Pipe Displacement of 9-1/2 casing 40 ppf in bbl/ft = (9.500^2 - 8.5^2) / 1029.4
Pipe Displacement of 9-1/2 casing 40 ppf in bbl/ft = 0.01749 bbl/ft

Ref: Pipe Displacement Calculation



How to calculate
Leak-Off Test Equivalent Mud Weight (EMW) = [Pressure (psi) / (0.052 x True Vertical Depth (ft)] + Mud Weight

Example:
Pressure = 520 psi
True Vertical Depth = 3195.5 ft
Mud Density/Weight = 9

EMW = [520 / (0.052 x 3195.5)] + 9 = Approximately 12.13 ppg



How to calculate Annular Velocity of Bottom Hole Assembly (BHA)
AV = Flow / Hole Diameter. First we need to calculate the average flow and then the Hole Diameter. Finally divide the two.

Example
Hole Size = 330 mm
Drill Pipe OD = 5 Inch = 127 mm
Average Flow = 200 gpm = 757.082 liters per minute (where 200gpm x 3.78541)

Hole Diameter = [(330^2) - (127^2) x 0.0007854 = 72.8623434

Annular Velocity = Average Flow / Hole Diameter = 757.082 / 72.8623434 = 10.39 m/min ~ 10.4 m/min
BHA

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