Well Control Kill Mud Weight and Circulating Pressure

ScopeThe mud weight that balances the formation, and the drillpipe pressures to hold while circulating it. Shut-in drillpipe pressure is the amount by which formation pressure exceeds the hydrostatic already in the hole, read directly at surface through a column of clean mud. Converting that pressure back into density is the same 0.052 relation rearranged, and the result is the weight that balances the formation with no surface pressure at all. The circulating pressures follow. Initial circulating pressure is the shut-in pressure plus whatever it takes to move mud at the slow rate; final circulating pressure is the slow-rate pressure scaled by the density ratio, since a heavier mud takes proportionally more pressure to circulate. Between them the drillpipe pressure is walked down on a schedule while kill mud goes to the bit, and it is held at the final value from there until the influx is out. The rounding question is where this gets dangerous, and it is why the rounded weight is an input here rather than a note. A kill weight rounded DOWN -- to a tidier number, or to what is already mixed -- leaves the well underbalanced by the difference, and the arithmetic that looks like it adds pressure actually subtracts it. The direction is therefore reported as a verdict computed from the two weights rather than as a signed number a reader has to interpret. Rounding UP is the safe direction and it has its own limit: excessive kill weight risks fracturing the formation at the shoe and turning a kick into an underground blowout, which is a check against the fracture gradient that this does not make. This is the driller's-method kill sheet for a vertical or near-vertical well with a clean drillpipe column: it does not check the casing shoe (the Kick Tolerance at the Casing Shoe calculator does that before the kick), handle a plugged or wet-string reading, account for influx type and migration, or model the annulus pressure profile or choke schedule. The ICP-to-FCP drillpipe schedule it gives is the wait-and-weight (engineer's) method; in the driller's method the second circulation holds casing pressure constant while kill mud goes to the bit. The operator's well control procedures, the certified kill sheet, and a qualified well-control supervisor govern.

Formula or tablekill mud weight = original weight + SIDPP / (0.052 x TVD); formation pressure = SIDPP + 0.052 x original weight x TVD; initial circulating pressure = SIDPP + slow-circulating-rate pressure; final circulating pressure = SCR pressure x (kill weight / original weight); strokes to the bit = drillpipe capacity x measured depth / pump output.

Source and editionThe driller's-method kill sheet as every well-control manual writes it. For a vertical or near-vertical well with a clean drillpipe column: it does not check the casing shoe (kick-tolerance does that before the kick), handle a plugged or wet string, account for influx type and migration, model the annulus pressure profile or the choke schedule, or check the fracture gradient.

Free accessOne kill sheet's arithmetic; no operator procedure is reproduced.

What governsEstimate. AHJ and licensed professional govern.

API field namesoriginal_mw_ppg, tvd_ft, sidpp_psi, scr_pressure_psi, safety_margin_ppg, rounded_mw_ppg, drillpipe_capacity_bbl_ft, measured_depth_ft, pump_output_bbl_stroke, pump_spm, formation_pressure_psi, kill_mw_ppg, icp_psi, fcp_psi, strokes_to_bit, rounded_bhp_change_psi

• Driller's method, clean drillpipe a plugged or wet string invalidates the surface readingthe operator's well control procedures
• No kick tolerance or shoe check the shoe is checked by kick-tolerance, before the kickthe certified kill sheet; kick-tolerance
• Vertical or near-vertical influx migration and the annulus profile are not modelleda qualified well-control supervisor