1. Basic Formulas

Table of Content

1. Pressure Gradient
2. Hydrostatic Pressure
3. Converting Pressure into Mud Weight
4. Specific Gravity
5. Equivalent Circulation Density
6. Maximum Allowable Mud Weight
7. Pump Output
8. Annular Velocity
9. Capacity Formulas
10. Control Drilling
11. Buoyancy Factor
12. Hydrostatic Pressure Decrease POOH
13. Loss of Overbalance Due to Falling Mud Level
14. Formation Temperature
15. Hydraulic Horsepower
16. Drill Pipe, Drill Collar Calculation
17. Pump Pressure, Pump Strokes
18. Cost Per Foot
19. Temperature Conversion Formulas

1.16 Drill Pipe/Drill Collar Calculations

Capacities, bbl/ft, displacement, bbl/ft, and weight, lb/ft, can be calculated from the following formulas:

$\mathrm{Capacity,\; bbl/ft}=\frac{{\mathrm{ID,\; in.}}^2}{1029.4}$
$\mathrm{Displacement,\; bbl/ft}=\frac{{\mathrm{OD,\; in.}}^2-{\mathrm{ID,\; in.}}^2}{1029.4}$
Weight, lb/ft = displacement, bbl/ft × 2747 lb/bbl

Example: Determine the capacity, bbl/ft, displacement, bbl/ft, and weight, lb/ft, for the following:
Drill collar OD = 8.0 in.
Drill collar ID = 2-13/16 in.
Convert 13/16 to decimal equivalent: 13 ÷ 16 = 0.8125
$\mathrm{Capacity,\; bbl/ft}=\frac{{2.8125}^2}{1029.4}$
Capacity = 0.007684 bbl/ft
$\mathrm{Displacement,\; bbl/ft}=\frac{{8.0}^2-{2.8125}^2}{1029.4}$
$\mathrm{Displacement,\; bbl/ft}=\frac{56.089844}{1029.4}$
Displacement = 0.0544879 bbl/ft
Weight, lb/ft = 0.0544879 bbl/ft × 2747 lb/bbl
Weight = 149.678 lb/ft

Rule of thumb formulas

Weight, lb/ft, for REGULAR DRILL COLLARS can be approximated by the following formula:

Weight, lb/ft = (OD, in.² − ID, in.²) × 2.66

Example: Regular drill collars Drill collar OD = 8.0 in.
Drill collar ID = 2-13/16 in.
Decimal equivalent = 2.8125 in.
Weight, lb/ft = (8.0² − 2.8125²) × 2.66
Weight, lb/ft = 56.089844 × 2.66
Weight = 149.19898 lb/ft

Weight, lb/ft, for SPIRAL DRILL COLLARS can be approximated by the following formula:

Weight, lb/ft = (OD, in.² − ID, in.²) × 2.56

Example: Spiral drill collars Drill collar OD = 8.0 in.
Drill collar ID = 2-13/16 in.
Decimal equivalent = 2.8 125 in.
Weight, lb/ft = (8.0² − 2.8125²) × 2.56
Weight, lb/ft = 56.089844 × 2.56
Weight = 143.59 lb/ft

⬆ Table of Content