Relevant Formulas used in Well Control

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) × 0.0981 × TVD (m) =

2. Pressure Gradient (bar/m) =

Mud Density (kg/l) × 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 Law

P1 x V1 = P2 x V2 P2 = (P1 x V1) / V2 V2 = (P1 x V1) / P2 P is pressure and V is volume at any given point in the well

19. Pressure drop (bar) per meter 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. Pressure drop (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 (meter)

[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. Length of tubulars (meters) to pull dry before overbalance is lost

Pressure Increase × Influx Volume ÷ (Formation − Pressure)

26. 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)]

27. 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)]

28. Pit gain (liters) due to slug U-tubing

[Slug volume (l) x [(Slug density (kg/l) / Drilling fluid density (kg/l)) – 1]]

29. 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)]

30. Hydrostatic pressure loss (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)]

31. Influx density

MW – [(SICP (bar) – SIDPP (bar)) / (Kick TVD (m) x 0.0981)]

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