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API (Field) Units Formula Sheet
Section 1. Filled-in Kill Sheet Exercises - Gauge Problem Actions.
Gauge Problem Exercises are constructed from a completed kill sheet ‘filled-in’ with all relevant volume and pressure calculations.
Each question is based on the strokes, pump rate, drill pipe and casing gauge readings at a specific point in time during a well kill operation. Any one or a combination of these readings could indicate the action required. Options are shown in the multiple-choice answers.
The casing and/or drill pipe pressures will only be relevant to the action if –
- The casing and/or drill pipe pressures given in the question are below the expected pressures, or
- The casing and/or drill pipe pressures given in the question are 70 psi or more above the expected pressures.
Section 2. Calculation Formula.
Abbreviations Used in this Document
bbl/ft = Barrels (US) per foot bbl/min = Barrels (US) per minute bbl/stroke = Barrels (US) per stroke BHP = Bottom Hole Pressure BOP = Blowout Preventer ft = Feet ft/hr = Feet per hour ft/min = Feet per minute lbs/bbl = Pounds per barrel LOT = Leak-off Test MAASP = Maximum Allowable Annular Surface Pressure ppg = Pounds per gallon psi = Pounds per square inch psi/ft = Pounds per square inch per foot psi/hr = Pounds per square inch per hour SICP = Shut in Casing Pressure SIDPP = Shut in Drill Pipe Pressure SPM = Strokes per minute TVD = True vertical depth 0.052 = Constant factor
1. HYDROSTATIC PRESSURE (psi)
Mud Density (ppg) x 0.052 x TVD (ft)
2. PRESSURE GRADIENT (psi/ft)
Mud Density (ppg) x 0.
3. DRILLING MUD DENSITY (ppg)
Pressure (psi) TVD (ft) x 0.
4. FORMATION PORE PRESSURE (psi)
Hydrostatic Pressure in Drill String (psi) + SIDPP (psi)
5. PUMP OUTPUT (bbl/min)
Pump Displacement (bbl/stroke) x Pump Rate (SPM)
6. ANNULAR VELOCITY (ft/min)
Pump Output (bbl/min) Annular Capacity (bbl/ft)
7. EQUIVALENT CIRCULATING DENSITY (ppg)
Annular Pressure Loss (psi) (^) + Mud Density (ppg) TVD (ft) x 0.
8. MUD DENSITY WITH TRIP MARGIN INCLUDED (ppg)
Safety Margin (psi) TVD (ft) x 0.
9. NEW PUMP PRESSURE WITH NEW PUMP RATE (psi) approximate
New Pump Rate (SPM)^2 Old Pump Pressure (psi) x Old Pump Rate (SPM)
10. NEW PUMP PRESSURE WITH NEW MUD DENSITY (psi) approximate
Old Pump Pressure (psi) x New Mud Density (ppg) Old Mud Density (ppg)
11. MAXIMUM ALLOWABLE MUD DENSITY (ppg)
Surface LOT Pressure (psi) (^) + LOT Mud Density (ppg) Shoe TVD (ft) x 0.
12. MAASP (psi)
[Maximum Allowable Mud Density (ppg) – Current Mud Density (ppg)] x 0.052 x Shoe TVD (ft)
13. KILL MUD DENSITY (ppg)
SIDPP (psi) (^) + Original Mud Density (ppg) TVD (ft) x 0.
14. INITIAL CIRCULATING PRESSURE (psi)
Kill Rate Circulating Pressure (psi) + SIDPP (psi)
15. FINAL CIRCULATING PRESSURE (psi)
Kill Rate Circulating Pressure (psi) x Kill Mud Density (ppg) Original Mud Density (ppg)
27. RISER MARGIN (ppg)
[Air Gap (ft) + Water Depth (ft)] x Mud Density (ppg) - [Water Depth (ft) x Sea Water Density (ppg)] TVD (ft) - Air Gap (ft) - Water Depth (ft)
28. BOP CLOSING RATIO
Wellhead Pressure at BOP (psi) Hydraulic Pressure Required to Close (psi)
29. BOP OPENING RATIO
Wellhead Pressure at BOP (psi) Hydraulic Pressure Required to Open (psi)
30. HYDROSTATIC PRESSURE LOSS IF CASING FLOAT FAILS
Mud Density (ppg) x 0.052 x Casing Capacity (bbl/ft) x Unfilled Casing Height (ft)
Casing Capacity (bbl/ft) + Annular Capacity (bbl/ft)
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