Relevant Formulas Used in Well Control

Formulas displayed in this section are commonly used in well-control calculations. Note; Formulas 16 and 25 are no longer part of the formulas in the IWCF formula sheets but are kept here for references.

1. HYDROSTATIC PRESSURE (bar) =

Mud Density (kg/l) x 0.0981 x TVD (m)

2. PRESSURE GRADIENT (bar/m) =

Mud Density (kg/l) x 0.0981

3. DRILLING MUD DENSITY (kg/l) =

Pressure (bar) ÷ [(TVD (m) x 0.0981)]

4. FORMATION PORE PRESSURE (bar) =

Hydrostatic Pressure in Drill String (bar) + SIDPP (bar)

5. PUMP OUTPUT (l/min) =

Pump Displacement (l/stroke) x Pump Rate (SPM)

6. ANNULAR VELOCITY (m/min) =

Pump Output (l/min) ÷ Annular Capacity (l/m)

7. EQUIVALENT CIRCULATING DENSITY (kg/l) =

Annular Pressure Loss (bar) ÷  [(TVD (m) x 0.0981)] + Fluid Density (kg/l)

8. MUD DENSITY WITH TRIP MARGIN INCLUDED (kg/l) =

Safety Margin (bar) ÷ [TVD (m) x 0.0981] + Mud Density (kg/l)

9. NEW PUMP PRESSURE (bar) WITH NEW PUMP RATE = (approximate)

Old Pump Pressure (bar) x [New Pump Rate (SPM)/ Old Pump Rate (SPM)]^2

10. NEW PUMP PRESSURE (bar) WITH NEW MUD DENSITY = (approximate)

Old Pump Pressure (bar) x [New Mud Density (kg/l)/ Old Mud Density (kg/l)]

11. MAXIMUM ALLOWABLE FLUID DENSITY (kg/l) =

[Surface LOT Pressure (bar) ÷ [(Shoe TVD (m) x 0.0981 )]]+ LOT Mud Density (kg/l)

12. MAASP (bar) =

[Maximum Allowable Mud Density (kg/l) – Current Mud Density (kg/l)] x 0.0981 x TVD (m)

13. KILL MUD DENSITY (kg/l) =

SIDPP (bar) ÷ [(TVD (m) x 0.0981)] + Original Mud Density (kg/l)

14. INITIAL CIRCULATING PRESSURE (bar) =

Kill Rate Circulating Pressure(up riser) (bar) + SIDPP (bar)

15. FINAL CIRCULATING PRESSURE (bar) =

[Kill Mud Density (kg/l) ÷ Original Mud Density (kg/l)] x Kill Rate Circulating Pressure (bar)

16. Baryte required to increase Drilling Mud Density (kg/l) =

[(Kill Mud Density (kg/l) – Original Mud Density (kg/l)) x 4.2] ÷ [4.2 – Kill Mud Density (kg/l)]

17. Gas Migration Rate (m/hr)

Rate of increase in Surface pressure (bar/hr) ÷ [Drilling Mud Density (kg/l) x 0.0981]

18. GAS LAWS

P₁xV₁ = P₂xV₂   P₂=(P₁xV₁)/V₂   V₂=(P₁xV₁)/P₂

P is pressure and V is volume at any given point  in the well

19. PRESSUREDROP (Bar) PER METRE TRIPPING DRY PIPE

[Drilling Mud Density (kg/l) x 0.0981 x Metal Displacement] / [Riser or Casing Capacity (l/m) – Metal Displacement (l/m)]

20. PRESSUREDROP (Bar) PER METRE TRIPPING WET PIPE

[Drilling Mud Density (kg/l) x 0.0981 x Closed End Displacement] / [Riser or Casing Capacity (l/m) – Closed End Displacement (l/m)]

21. LEVEL DROP (meters) PULLING REMAINING COLLARS OUT OF HOLE DRY

[Length of Collars (m) x Metal Displacement (l/m)] / [Riser or Casing Capacity l/m]

22. LEVEL DROP (meters) PULLING REMAINING COLLARS OUT OF HOLE WET (metre)

[Length of Collars (m) x Closed End Displacement (l/m)] / [Riser or Casing Capacity l/m]

23. LENGTH OF TUBULARS (meters) TO PULL DRY BEFORE OVERBALANCE IS LOST

Overbalance (bar) x [Riser or Casing Capacity (l/m) – Metal Displacement (l/m)] / [Drilling Mud Gradient (bar/m) x Metal Displacement (l/m)]

24. LENGTH OF TUBULARS (meters) TO PULL WET BEFORE OVERBALANCE IS LOST

Overbalance (bar) x [Riser or Casing Capacity (l/m)- Closed End Displacement (l/m))] / [Drilling Mud Gradient (bar/m) x Closed End Displacement (l/m)]

25. VOLUME TO BLEED (liters) OFF TO RESTORE BHP TO FORMATION PRESSURE

[Increase in Surface pressure (bar) x Influx Volume (l)] / [Formation Pressure (bar) – Increase in Surface Pressure (bar)]

26. SLUG VOLUME (liter) FOR A GIVEN LENGTH OF DRY PIPE

[Length of Dry Pipe (m) x Pipe Capacity (l/m) x Drilling Mud Density (kg/l)] / [Slug Density (kg/l) – Drilling Fluid Density (kg/l)]

27. PITGAIN (liters) DUE TO SLUG U-TUBING

[Slug Volume (l) x [(Slug Density (kg(l) / Drilling Fluid Density (kg/l)) – 1]

28. RISER MARGIN (kg/l)

[(Air Gap (m) + Water Depth (m)) x Mud Density (kg/l)] – [Water Depth (m) x Sea Water Density (kg/l)] / [TVD (m)- Air Gap (m) – Water Depth (m)]

29. HYDROSTATIC PRESSURELOSS (Bar) IF CASING FLOAT FAILS

[Mud Density (kg/l) x 0.0981 x Casing Capacity (l/m) x Unfilled Casing Height (m)] / [Casing Capacity (l/m) + Annular Capacity (l/m)]

Other, 1: Influx Density

MW – [(SICP(bar)-SIDPP(Bar))/(KickTVD(m) x 0,0981)]