Kill Sheet Step-by-Step: Driller's Method or Wait and Weight?
Lesson Summary
Learn how to fill out a kill sheet, calculate kill mud weight and circulation pressures, and the practical difference between the Driller's Method and the Wait and Weight method.
This lesson is part of the Well Control track and lasts 11:45 minutes. Watch the video first, then review the key points and test your understanding with the questions below.
Key Points
- 1Kill Mud Weight (KMW) = Current Weight + SIDPP ÷ (0.052 × TVD)
- 2Use SIDPP, not SICP, for calculations
- 3Driller's Method: Two circulations, the first to circulate out the kick
- 4Wait and Weight: One circulation with kill mud
Written Lesson
What does a Kill Sheet contain?
A Kill Sheet is the written action plan to circulate a kick out of the well and restore primary control using the constant bottomhole pressure principle. It is divided into three parts:
- Pre-recorded data: True Vertical Depth TVD and Measured Depth MD, current mud weight, pipe and annulus capacities, pump displacement (bbl/stroke), Slow Circulating Rate pressure (SCR) for each pump at specific rates, and Leak-Off Test results at the casing shoe.
- Kick data: Shut-in drill pipe pressure (SIDPP), shut-in casing pressure (SICP), and pit gain volume.
- Calculations: Kill Mud Weight (KMW), Initial and Final Circulating Pressures (ICP/FCP), strokes from surface to bit, pressure drawdown schedule, and MAASP.
Why SIDPP and not SICP?
The drill string is filled with mud of a known density, whereas the annulus contains an influx of unknown density. Therefore, SIDPP provides a direct pressure gauge of the difference between formation pressure and the hydrostatic pressure of the mud in the pipe. SICP is usually higher because the lighter influx in the annulus reduces the hydrostatic pressure there.
KMW = OMW + SIDPP ÷ (0.052 × TVD)
ICP = SCR + SIDPP
FCP = SCR × KMW ÷ OMW
Full Example
Worked Example: Data: TVD = MD = 10,000 ft, mud weight 10.0 ppg, SIDPP = 520 psi, SICP = 750 psi, and SCR 600 psi at 30 spm. Kill Mud Weight (KMW) = 10.0 + 520 ÷ (0.052 × 10,000) = 10.0 + 520 ÷ 520 = 11.0 ppg. Initial Circulating Pressure ICP = 600 + 520 = 1,120 psi. Final Circulating Pressure FCP = 600 × 11.0 ÷ 10.0 = 660 psi.
Worked Example: String volume: 9,000 ft of Drill Pipe at 0.01776 bbl/ft gives 159.8 bbl, and 1,000 ft of Drill Collars at 0.0077 bbl/ft gives 7.7 bbl, total ≈ 167.5 bbl. With a pump displacement of 0.1 bbl/stroke, strokes to bit = 167.5 ÷ 0.1 ≈ 1,675 strokes, which is about 56 minutes at 30 spm. Drill pipe pressure drops from 1,120 to 660 psi during this time, or (1,120 − 660) ÷ 16.75 ≈ 27.5 psi per 100 strokes.
In practice, we round the kill mud weight up to the nearest 0.1 ppg if the result is not an exact figure. Slow circulating rates (SCR) should be recorded every shift or after any change in mud properties or BHA as they will change.
MAASP and Updates
MAASP is the maximum allowable surface pressure in the annulus before the formation at the casing shoe breaks down, and is calculated from the leak-off test.
MAASP = (LOT EMW − MW in annulus) × 0.052 × Shoe TVD
Worked Example: Casing shoe at 5,000 ft TVD and Leak-Off Test equivalent weight of 14.5 ppg. With 10.0 ppg mud: MAASP = (14.5 − 10.0) × 0.052 × 5,000 = 4.5 × 260 = 1,170 psi. After kill mud of 11.0 ppg fills the annulus above the shoe: MAASP = (14.5 − 11.0) × 260 = 910 psi. Therefore, MAASP must be updated whenever the mud weight in the annulus changes.
Driller's Method
- First circulation: Bring the pump up to the slow circulating rate while holding casing pressure constant with the choke, then hold drill pipe pressure constant at ICP until the kick is fully circulated out using the original mud.
- Second circulation: Pump kill mud. From surface to bit, hold casing pressure constant. Once kill mud reaches the bit, hold drill pipe pressure constant at FCP until kill mud returns to surface.
Advantages include simplicity and starting kick removal immediately without waiting to weight up mud. The disadvantage is the two circulations and typically higher annulus pressures during the first circulation.
Wait and Weight Method
Shut in the well and prepare kill mud first, then circulate the kick out and kill the well in one circulation. Drill pipe pressure drops according to the schedule from ICP to FCP while pumping to the bit, then stays at FCP. It often results in lower pressure at the casing shoe if kill mud reaches the annulus before gas reaches the shoe, and less time under pressure. However, it requires weighting-up time during which gas bubbles migrate, requiring pressure monitoring while waiting.
Summary
- Calculate kill mud weight from SIDPP because the drill string mud density is known.
- ICP = SCR + SIDPP, and FCP = SCR × KMW ÷ OMW, with a drawdown schedule in between based on strokes.
- MAASP changes with the mud weight in the annulus and must be updated.
- Driller's Method: Two circulations and immediate start. Wait and Weight: One circulation and often lower pressures.
The figures and examples in this lesson are for educational purposes. On the job, always follow your company procedures and accredited training center instructions.
Test Yourself
Lesson Glossary
Pump pressure at a specific slow rate, pre-measured and used to calculate kill pressures.
Drill pipe pressure at the start of the kill: SCR + SIDPP.
Drill pipe pressure after kill mud reaches the bit: SCR × KMW ÷ OMW.
The limit at which the formation fractures at the casing shoe.
The principle of all kill methods: keeping bottomhole pressure constant and slightly above formation pressure.
Vertical distance from surface to a given point; used for all pressure calculations.
Influx of formation fluids into the wellbore when bottomhole pressure falls below formation pore pressure.
Drill string pressure measured after shut-in, used to calculate formation pressure and kill mud weight.
Pressure in the annulus after shut-in, directly affected by the type and volume of the influx.
The weight that balances formation pressure: MW + SIDPP ÷ (0.052 × TVD).