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

1.17 Pump Pressure/Pump Stroke Relationship (Also Called the Roughneck’s Formula)

Basic formula

New circulating pressure, psi = present circulating pressure, psi × (new pump rate, spm ÷ old pump rate, spm)²

Example: Determine the new circulating pressure, psi using the following data:
Present circulating pressure = 1800 psi
Old pump rate = 60 spm
New pump rate = 30 spm
New circulating pressure, psi = 1800 psi × (30 spm ÷ 60 spm)²
New circulating pressure, psi = 1800 psi × 0.25
New circulating pressure = 450 psi

Determination of exact factor in above equation

The above formula is an approximation because the factor “2” is a rounded-off number. To determine the exact factor, obtain two pressure readings at different pump rates and use the following formula:

$\mathrm{Factor}=\frac{log(\mathrm{pressure1}÷\mathrm{pressure2})}{log(\mathrm{pump\; rate1}÷\mathrm{pump\; rate2})}$

Example: Pressure 1 = 2500 psi @ 315 gpm Pressure 2 = 450 psi ~ 120 gpm
$\mathrm{Factor}=\frac{log(\mathrm{2500\; psi}÷\mathrm{450\; psi})}{log(\mathrm{315\; gpm}÷\mathrm{120\; gpm})}$
$\mathrm{Factor}=\frac{log\left(5.5555556\right)}{log\left(2.625\right)}$
Factor = 1.7768

Example: Same example as above but with correct factor:
New circulating pressure, psi = 1800 psi × (30 spm ÷ 60 spm)^1.7768
New circulating pressure, psi = 1800 psi × 0.2918299
New circulating pressure = 525 psi

⬆ Table of Content