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

1.18 Cost Per Foot

$\mathrm{CT}=\frac{B+\mathrm{CR}\times (t+T)}{F}$

Example: Example: Determine the drilling cost (CT), dollars per foot using the following data:
Bit cost (B) = $2500
Rotating time (t) = 65 hours
Rig cost (CR) = $900/hour
Round trip time (T) = 6 hours (for depth - 10,000 ft)
Footage per bit (F) = 1300 ft
$\mathrm{CT}=\frac{\mathrm{2500}+\mathrm{900}\times (\mathrm{65}+6)}{1300}$
$\mathrm{CT}=\frac{\mathrm{66,400}}{1300}$
CT = $51.08 per foot

⬆ Table of Content