Why 0.052 psi/ft/ppg?

Conversion: 1 ppg × 7.48 gal/ft³ ÷ 144 in²/ft² × 1 lb/gal = 0.052 psi/ft/ppg. Water at 8.34 ppg yields 0.052 × 8.34 = 0.434 psi/ft hydrostatic, the well-known fresh-water gradient.

Should kill mud be exactly KMW or a margin?

IADC and IWCF training recommend a 0.2–0.3 ppg trip margin above computed KMW for overbalance. NORSOK D-010 in Norway specifies a minimum 25 bar (about 0.7 ppg at typical depth) overbalance for primary well barriers.

Driller's Method Kill Sheet Calculator

A kick is detected. Shut in the well, read SIDPP and SICP off the choke manifold, and run the Driller's Method calc. Returns kill mud weight, initial and final circulating pressure, strokes to bit, strokes bit-to-surface, total circulation strokes, and kill mud volume.

Hydrostatic constant

0.052psi/ft/ppg

IADC trip margin

0.2–0.3ppg

Driller's circulations

W&W circulations

True vertical depth (ft) TVD drives hydrostatic; MD drives volumes & strokes

Measured depth (ft) Total drilled length along the wellbore

Drill pipe length (ft) From rotary table to top of drill collars

Drill collar length (ft) BHA length below DP

DP internal capacity (bbl/ft) 5" DP × 4.276" ID = 0.01776 bbl/ft (per IADC handbook)

DC internal capacity (bbl/ft) 8" × 3" ID drill collar = 0.0061 bbl/ft

Annular DP × hole (bbl/ft) 5" DP × 8.5" open hole = 0.0459 bbl/ft

Annular DC × hole (bbl/ft) 8" DC × 8.5" hole = 0.0292 bbl/ft

Pump output (bbl/stk) Triplex 7" × 12" @ 95% efficiency typical

SCR pressure at original MW (psi) Slow Circulating Rate friction; recorded each tour

Original mud weight (OMW) (ppg) Mud weight in active system before kick

SIDPP — shut-in DP pressure (psi) Read after stable shut-in (5–10 min)

SICP — shut-in casing pressure (psi) SICP > SIDPP indicates lighter influx (gas) in annulus

Pit gain (bbl) Active-pit volume increase from kick

Kill mud weight (KMW)

—ppg

Enter values

ICP

—psi

FCP

—psi

Strokes to bit

—stk

Strokes bit→surface

—stk

Kill mud volume

—bbl

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Tip The Driller's Method circulates the influx out FIRST at original mud weight (one full annulus circulation), THEN circulates kill mud in second at FCP. Wait-and-Weight kills in one circulation but needs the heavier mud already mixed. Driller's = simpler / faster to start; W&W = lower casing-shoe pressure peak.

Warn Always verify casing-shoe pressure stays below the LOT (Leak-Off Test) or FIT (Formation Integrity Test) value during the kill — exceed it and you fracture the formation, losing the well. ICP at the shoe = SIDPP + 0.052 × OMW × TVD_shoe. If shoe pressure exceeds LOT, switch to a Volumetric Method (lubricate & bleed or bullhead) — this calculator does NOT model lubrication or bullheading.

Worked example

10,000 ft TVD vertical well, 11.5 ppg mud, 5" drill pipe (9,500 ft) over 1,000 ft of 8" drill collars. Pumping at SCR 800 psi. Kick detected, well shut in: SIDPP = 350 psi, SICP = 450 psi, pit gain 10 bbl.

1. Kill mud weight KMW = OMW + SIDPP / (0.052 × TVD) KMW = 11.5 + 350 / (0.052 × 10,000) KMW = 11.5 + 0.673 KMW = 12.17 ppg → round up to 12.2 ppg 2. Initial circulating pressure ICP = SIDPP + SCR ICP = 350 + 800 ICP = 1,150 psi 3. Final circulating pressure FCP = SCR × (KMW / OMW) FCP = 800 × (12.17 / 11.5) FCP = 846 psi 4. Strokes to bit (drill string) String volume = (DP × DPcap) + (DC × DCcap) = (9,500 × 0.01776) + (1,000 × 0.0061) = 168.7 + 6.1 = 174.8 bbl Strokes = 174.8 / 0.117 ≈ 1,494 strokes to bit 5. Strokes bit → surface (annulus) Annulus volume = (DC × DCannular) + ((MD − DC) × DPannular) = (1,000 × 0.0292) + (9,500 × 0.0459) = 29.2 + 436.05 = 465.2 bbl Strokes = 465.2 / 0.117 ≈ 3,977 strokes bit-to-surface 6. Kill mud volume Vol = string + annulus + 50 bbl active min = 174.8 + 465.2 + 50 = 690 bbl kill mud needed

Sources

API RP 53 Blowout Prevention IADC Well Control Manual IWCF Surface BOP curriculum Aadnøy Modern Well Design (2nd ed.) SPE Bourgoyne, Applied Drilling Engineering Vol. 2

Common mistakes

Confusing TVD and MD. Hydrostatic pressure uses TVD; circulation volumes and strokes use MD. Mixing them on a deviated well underestimates KMW.
Forgetting SCR is at OMW. FCP must scale by KMW / OMW. Using SCR directly as FCP under-pressures the system once kill mud reaches the bit.
Mixing imperial and metric units. This calculator is imperial only (bbl, ppg, psi). Metric well control uses 0.0981 bar/m/sg and m³ — do not mix.

FAQ

Why is FCP lower than ICP?

As kill mud progresses down the drill pipe, the heavier column inside the string means less surface pressure is required to maintain bottomhole balance. ICP includes SIDPP plus pump friction at original mud weight; FCP scales pump friction by the ratio KMW / OMW only.

Driller's vs Wait-and-Weight?

Driller's Method uses two circulations: kick out at original mud weight, then kill mud in. Wait-and-Weight does it in one circulation but requires the heavier mud already mixed and ready. W&W has lower peak casing-shoe pressure but a longer pre-job interval; Driller's starts immediately.

Where does 0.052 psi/ft/ppg come from?

Conversion factor: 1 ppg × 7.48 gal/ft³ ÷ 144 in²/ft² × 1 lb/gal = 0.052 psi/ft/ppg. Water at 8.34 ppg gives 0.052 × 8.34 = 0.434 psi/ft, the standard fresh-water gradient.

Should kill mud be exactly KMW or carry a margin?

IADC / IWCF training recommends a 0.2–0.3 ppg trip margin above computed KMW to provide overbalance. Some operators add 0.5 ppg. NORSOK D-010 (Norwegian regulator) specifies a minimum 25 bar overbalance for primary well barriers — about 0.7 ppg at 10,000 ft.

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Oil & Gas Toolkit runs kill-mud, ECD and pump output from SIDPP and TVD, shows the math, and prints a kill sheet. No signal, no login. Pay once.