Kill Sheet Calculator: Kill Mud Weight, ICP, FCP, and Pressure Schedule

When a well kicks and the BOP closes, the panic is over and the arithmetic begins. The shut-in drillpipe pressure is the reservoir speaking directly to you: with a known column of mud between the gauge and the formation, SIDPP tells you exactly how underbalanced you are. The kill sheet is the disciplined little worksheet that turns that number into a plan, and every well control certification on earth drills the same calculation because getting it right under pressure, literally, is the whole job.

The four numbers

• Kill mud weight: KMW = OMW + SIDPP / (0.052 x TVD). The density that exactly balances the formation, before any safety margin
• Initial circulating pressure: ICP = SIDPP + SCRP, where SCRP is the pre-recorded pump pressure at kill rate with the old mud
• Final circulating pressure: FCP = SCRP x KMW / OMW, the friction pressure once heavy mud fills the string
• Strokes to bit: drill string volume divided by pump output, which sets the length of the step-down schedule

Bring the pump up to kill speed holding casing pressure constant, and the drillpipe gauge should read close to ICP. From there, the schedule is a straight line: as kill mud displaces old mud down the string, reduce drillpipe pressure linearly so that when the heavy mud reaches the bit, the gauge reads FCP. Then hold FCP until kill mud makes it all the way around. Follow the drillpipe gauge on the way down and the choke does the rest; that is the wait and weight method this calculator builds.

Worked example

• 10 ppg mud, 10,000 ft TVD, SIDPP 500 psi, SICP 650 psi, SCRP 800 psi at kill rate
• KMW = 10 + 500/520 = 10.96 ppg
• ICP = 1,300 psi, FCP = 800 x 10.96/10 = 877 psi
• 130 bbl string at 0.1 bbl/stroke gives 1,300 strokes to bit; the schedule steps 1,300 down to 877 psi across them

Details that separate a clean kill from a messy one

SCRP is the number people regret not having: it must be measured and recorded regularly at reduced pump rates before you need it, because after shut-in there is no clean way to get it. The SIDPP reading itself deserves skepticism if a float valve is in the string (it needs bumping to read through) or if gas has migrated during a long shut-in, which inflates both gauges. And notice what SICP is for: it does not enter the kill arithmetic directly, but the gap between SICP and SIDPP is your influx severity gauge, since a bigger gap means lighter influx in the annulus, almost always gas. Finally, this sheet computes the balanced kill weight deliberately without a margin; companies add their own trip margin on top, and mixing policy margin into the physics is a classic source of confusion when two calculations disagree.

Related Calculators and Reference

The pressure limit the annulus can tolerate during the kill comes from the kick tolerance calculator, the mud weight conversions use the same relationships as the mud weight and hydrostatic pressure calculator, and the fracture limit at the shoe traces back to the fracture gradient calculator. The PetroWiki page on well control covers the wait and weight method in full.