bottoms-up

Bottoms-up circulation in well control kill operations defines the number of pump strokes and circulating time required to displace the entire drill string fluid volume from the bit to surface during a controlled kick circulation event in Western Canada Sedimentary Basin wells, where the kill sheet driller's method or wait-and-weight method requires the drilling crew to track the exact pump stroke count from the moment kill fluid is pumped into the drill string until that kill fluid reaches the bit (drill string bottoms-up), and then from the bit through the annulus until the original formation influx and contaminated mud are circulated entirely out of the wellbore (annulus bottoms-up), with the kill operation complete only when kill-weight mud has filled both the drill string and the annulus from bit to surface and the shut-in casing pressure has bled to zero. The bottoms-up stroke count for a WCSB kill operation is calculated from the drill string internal volume divided by the pump output per stroke: for a typical WCSB Montney horizontal well with 5-inch drill pipe (capacity 0.00817 m3/m) from surface to 4,000 m, a 7-inch heavy-weight drill pipe section (capacity 0.00563 m3/m) from 3,800 to 4,100 m, and 6.75-inch drill collars (capacity 0.00278 m3/m) from 4,100 to 4,200 m, the total drill string volume is approximately 35.1 m3; at a triplex pump output of 0.0152 m3/stroke (9.3 L/stroke at 100% volumetric efficiency), the drill string bottoms-up stroke count is 35.1/0.0152 = 2,309 strokes, representing the number of strokes at the kill circulation rate before kill fluid reaches the bit and the driller can begin monitoring the kill line pressure at the drill bit depth. The annulus bottoms-up calculation adds the annular volume from bit to surface using the same capacity methodology, and in WCSB horizontal wells the annular volume calculation must separately account for the open-hole section (bit to casing shoe), the 9.625-inch or 13.375-inch casing section from shoe to surface, and any liner or liner-tieback string above the production casing, because each interval contributes a different annular capacity per metre based on casing ID and drill pipe OD combinations that govern how many strokes the pump must deliver to sweep the influx-contaminated mud column from the bottom of the wellbore to the surface shaker where the gas show or saltwater kick volume can be visually confirmed to have exited the wellbore. Understanding bottoms-up stroke calculation methodology for WCSB well control (drill string volume calculation, pump output measurement and correction for liner wear and volumetric efficiency, annular capacity tables for each wellbore section), the kill sheet documentation required under AER Directive 036 for all WCSB wells above H2S threshold concentrations, the difference between the driller's method (two-circulation kill) and the wait-and-weight method (single-circulation kill) in terms of how bottoms-up stroke count determines each method's execution timeline, and how bottoms-up lag time in the annulus governs the timing of pit volume gain monitoring and choke adjustment during a WCSB kick circulation gives WCSB drilling supervisors, company men, and drilling engineers the well control operational framework to execute controlled kick circulations safely and to detect errors in kill execution from anomalous surface pressure or pit volume responses relative to the bottoms-up stroke schedule.

• Kill sheet stroke count calculation for WCSB Montney horizontal well driller's method: In the driller's method for a WCSB Montney horizontal kick, the kill sheet documents two separate circulation sequences. Circulation 1 (original mud weight, kick circulated out): begins at shut-in, circulates from pump to bit (drill string bottoms-up at stroke count S1) then from bit around the annulus to surface (annulus bottoms-up at additional stroke count S2); total strokes for circulation 1 = S1 + S2 = drill string strokes + annulus strokes. Circulation 2 (kill mud, wellbore displaced to kill weight): begins immediately after circulation 1, displaces drill string to kill weight mud at S1 strokes, then displaces annulus at S2 additional strokes. For a WCSB Montney well with S1 = 2,309 drill string strokes and S2 = 4,850 annulus strokes at the kill rate of 600 L/min (0.94 m3/min), total kill time for both circulations is approximately (2 x 2,309 + 2 x 4,850) strokes x 0.0152 m3/stroke / 0.94 m3/min = 233 minutes (3 hours 53 minutes), assuming constant pump rate throughout.
• Pump output measurement and stroke counter calibration for WCSB kill operation accuracy: The accuracy of bottoms-up stroke prediction in a WCSB well control event depends entirely on knowing the actual pump output per stroke at the kill circulation rate, which may differ from the theoretical output due to liner wear, piston seal bypass, and valve leakage that reduce the pump's volumetric efficiency below 100%. WCSB well control procedures require a pump output test at the kill rate before the well is spudded: the pump is stroked for a known number of strokes (minimum 100 strokes) into a calibrated pit volume reference, and the measured fill per 100 strokes is divided by 100 to get actual output per stroke; a new pump may deliver 0.0154 m3/stroke (101% of rated 0.0152) while a worn pump may deliver 0.0141 m3/stroke (93% of rated). AER Directive 036 requires that the pump output calibration be performed at least weekly during drilling and recorded on the daily drilling report; using uncalibrated pump output in kill sheet calculations can produce bottoms-up stroke count errors of 5 to 10%, causing kill fluid to reach the bit 110 to 230 strokes early or late relative to schedule, confusing the driller's interpretation of the choke pressure response during kill operations.
• Annulus bottoms-up lag monitoring and choke management during WCSB gas kick circulation: During a WCSB gas kick circulation, the annular bottoms-up stroke schedule governs when the driller expects the gas influx to reach progressively shallower depths in the annulus, where gas expansion (Boyle's Law) causes the pit volume to increase at a rate predictable from the bottoms-up stroke count and the annular capacity at each depth interval. For a WCSB Montney well where 3 m3 of gas influx was taken at 4,200 m MD (TVD 3,800 m, reservoir pressure 38 MPa), the gas occupies 3 m3 at 38 MPa; as it migrates to 2,000 m TVD (approximately 20 MPa hydrostatic), it expands to 5.7 m3, and at surface (0.1 MPa) it would expand to 1,140 m3 if uncontrolled. The choke operator maintains back-pressure on the annulus by adjusting the choke opening to keep the drill pipe pressure on the kill schedule curve while the pit volume gain is monitored continuously; the bottoms-up stroke count at each depth interval tells the choke operator when to expect the expanding gas slug to reach the BOP and prepare for maximum choke restriction as the influx exits the wellbore.
• Wait-and-weight method kill schedule and bottoms-up stroke profile in WCSB H2S wells: In WCSB sour gas wells (above H2S threshold requiring H2S well control procedure), the wait-and-weight (W&W) method is preferred over the driller's method because it requires only one circulation, minimizing the duration of the kick-in-wellbore condition that exposes the casing and BOP to H2S at high partial pressure. The W&W kill schedule plots drill pipe pressure (y-axis) versus strokes pumped (x-axis) as a straight line from the initial circulating pressure (ICP) at stroke 0 to the final circulating pressure (FCP) at stroke S1 (drill string bottoms-up), then holding FCP constant from S1 to S1 + S2 (annulus bottoms-up) while the kill mud displaces the annular kick fluid. The kill sheet for WCSB H2S wells at AER-designated H2S release rate risk above threshold must include both the W&W drill pipe pressure schedule and the minimum casing pressure limits derived from the AER Directive 036 maximum allowable annular surface pressure, with the choke operator maintaining casing pressure above the minimum limit throughout the bottoms-up circulation to prevent secondary influx of H2S-bearing formation fluid into the wellbore during the single-circulation kill.
• Bottoms-up stroke count verification after drill string geometry changes in WCSB lateral drilling: WCSB horizontal well kill sheets must be updated each time the drill string geometry changes during the drilling program, because adding drill pipe joints as the lateral extends, replacing drill collars with heavyweight drill pipe in the curve section, or installing MWD/LWD tools with non-standard bore IDs all change the drill string internal volume and therefore the bottoms-up stroke count. A WCSB Montney lateral extension of 500 m using 5-inch drill pipe (capacity 0.00817 m3/m) adds 4.085 m3 to the drill string volume, requiring 269 additional drill string bottoms-up strokes at the calibrated pump output; if the kill sheet is not updated and a kick is taken at the new measured depth, the driller will deliver kill weight mud to the bit 269 strokes too early, prematurely terminating the constant drill pipe pressure phase of the W&W kill and causing underpressure at the bit that risks a secondary influx before the full kill weight mud column is established in the drill string.

Bottoms-Up Stroke Count Error Leading to Extended Kick Circulation on a WCSB Duvernay Well

A west-central Alberta Duvernay horizontal well took a 2.1 m3 gas kick while drilling at 5,840 m measured depth (TVD 4,150 m). The well was shut in with 3.8 MPa SIDPP and 5.1 MPa SICP; kill mud weight was calculated at 1.94 kg/L versus the original 1.82 kg/L mud. The kill sheet was prepared using the drill string bottoms-up from the previous morning's calculation at 5,600 m measured depth, which had not been updated after 240 m of additional lateral footage drilled using 5-inch drill pipe. The uncorrected drill string bottoms-up stroke count was 3,410 strokes versus the correct value of 3,570 strokes at 5,840 m. The driller shifted from constant drill pipe pressure to constant casing pressure at stroke 3,410, 160 strokes before kill mud reached the bit; during those 160 strokes with no pressure adjustment, the drill pipe pressure dropped by 1.2 MPa below the W&W schedule, allowing 0.4 m3 of additional gas to enter the wellbore from the Duvernay. The secondary influx extended the total kick circulation by 48 minutes and required 0.9 MPa additional choke restriction as the expanded secondary gas slug exited the annulus. Post-incident review identified the kill sheet update failure and implemented a mandatory kill sheet recalculation at each 200 m drilled increment as an AER reportable corrective action.

Related Terms

Bottoms-up is the primary entry covering bottoms-up lag time for cuttings and gas show correlation during normal drilling; this companion entry covers bottoms-up stroke count calculation in well control kill operations, where drill string and annulus displacement volumes determine the kill execution schedule for driller's method and wait-and-weight procedures in WCSB wells. Well control is the engineering discipline that establishes the kill sheet methodology, stroke count calculation standards, and choke management procedures governing WCSB kick circulation; AER Directive 036 requirements for kill sheet documentation, pump calibration, and H2S well control procedures frame the well control environment within which bottoms-up stroke scheduling is applied. Kill sheet is the document that records the bottoms-up stroke counts, kill mud weight calculation, and drill pipe pressure schedule for a WCSB well control event; errors in the kill sheet stroke calculation from outdated drill string geometry or uncalibrated pump output are among the most common technical causes of extended kick circulation events in WCSB horizontal well programs. Choke manifold is the surface pressure control assembly used by the choke operator to maintain back-pressure on the annulus during WCSB kick circulation; the bottoms-up stroke schedule tells the choke operator when the expanding gas slug will reach specific annular depths, guiding choke adjustments to prevent casing pressure from exceeding formation fracture pressure while keeping surface pressure above the minimum required to prevent secondary influx. Blowout preventer (BOP) provides the pressure-sealing barrier that allows controlled kick circulation in WCSB wells; the BOP must remain closed on the drill pipe throughout the bottoms-up circulation until kill-weight mud fills the annulus from bit to surface and casing pressure bleeds to zero, confirming that the formation influx has been fully displaced.