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

1.13 Loss of Overbalance Due to Falling Mud Level

Feet of pipe pulled DRY to lose overbalance

$\mathrm{Feet}=\frac{\mathrm{overbalance,\; psi}\times (\mathrm{casing\; capacity,\; bbl/ft}-pipe\; displacement,\; bbl/ft)}{\mathrm{mud\; weight,\; ppg}\times 0.052\times \mathrm{pipe\; displacement,\; bbl/ft}}$

Example: Determine the FEET of DRY pipe that must be pulled to lose the overbalance using the following data:
Amount of overbalance = 150 psi, Casing capacity = 0.0773 bbl/ft, Pipe displacement = 0.0075 bbl/ft, and, Mud weight = 11.5 ppg
$\mathrm{Feet}=\frac{\mathrm{150\; psi}\times (\mathrm{0.0773\; bbl/ft}-0.0075\; bbl/ft)}{\mathrm{11.5\; ppg}\times 0.052\times \mathrm{0.0075\; bbl/ft}}$
$\mathrm{Feet}=\frac{10.47}{0.004485}$
Feet = 2334

Feet of pipe pulled WET to lose overbalance

$\mathrm{Feet}=\frac{\mathrm{overbalance,\; psi}\times (\mathrm{casing\; capacity,\; bbl/ft}-pipe\; capacity,\; bbl/ft-pipe\; displacement,\; bbl/ft)}{\mathrm{mud\; weight,\; ppg}\times 0.052\times (\mathrm{pipe\; capacity,\; bbl/ft}+\mathrm{pipe\; displacement,\; bbl/ft})}$

Example: Determine the feet of WET pipe that must be pulled to lose the overbalance using the following data:
Amount of overbalance = 150 psi, Casing capacity = 0.0773 bbl/ft, Pipe capacity = 0.01776 bbl/ft, Pipe displacement = 0.0075 bbl/ft, and, Mud weight = 11.5 ppg
$\mathrm{Feet}=\frac{\mathrm{150\; psi}\times (\mathrm{0.0773\; bbl/ft}-0.01776\; bbl/ft-0.0075\; bbl/ft)}{\mathrm{11.5\; ppg}\times 0.052\times (\mathrm{0.01776\; bbl/ft}+\mathrm{0.0075\; bbl/ft})}$
$\mathrm{Feet}=\frac{\mathrm{150\; psi}\times \mathrm{0.05204\; bbl/ft}}{\mathrm{11.5\; ppg}\times 0.052\times \mathrm{0.02526\; bbl/ft}}$
$\mathrm{Feet}=\frac{7.806}{0.0151054}$
Feet = 516.8

⬆ Table of Content