IWCF Level 4 Drilling common mistakes
IWCF Level 4 Drilling · Understand the traps and how to avoid them.
Treating the slow circulating rate pressure (SCR) as a fixed number memorised from a prior well and using it unchanged for kill-sheet calculations.
Candidates confuse the SCR recorded on a previous well, or the initial circulating pressure at full kill rate, with the current well's measured SCR at the reduced kill rate. They also forget that SCR must be re-recorded when mud weight, pump liner, or hole depth changes, so the figure they apply is stale.
What to do instead
Before every calculation, confirm the SCR was taken on the current well at the same pump rate and with the current mud weight, and state the pump rate and SPM alongside the pressure. Re-record SCR after any mud weight increase, pump change, or significant depth change, and show the source of the number in the answer so the examiner can see it came from the current well data.
Calculating kill mud weight from the original mud weight plus the SIDPP converted with the wrong formula constant, or mixing the pressure gradient units (psi/ft versus kPa/m versus bar/m) within one answer.
Candidates learn one constant (0.052 for psi/ft with ppg) and apply it when the question is set in SI units, or they use 0.0519 and 0.052 interchangeably and lose marks on rounding. Unit mixing happens because the exam mixes field and SI conventions across questions and candidates do not re-read the units in each stem.
What to do instead
Write the unit line first: identify whether the stem gives ppg, kg/m3, or SG, and whether depth is ft or m, then select the correct constant (0.052 psi/ft per ppg; 0.00981 kPa/m per kg/m3). Carry units through every step of the calculation and convert final answers back to the units the question asks for, showing the conversion explicitly.
On a kick sheet, filling in the final circulating pressure and the pressure-versus-stroke schedule without converting the initial circulating pressure to the kill rate before applying the kill mud weight ratio.
Candidates jump straight from SIDPP and SICP to the schedule and forget that the first step is to establish the initial circulating pressure at the slow rate, then reduce it by the ratio of kill mud weight to original mud weight. They also forget to subtract SIDPP from SICP before adding SIDPP to the circulating pressure, which produces a plausible but wrong FCP.
What to do instead
Work the kill sheet in a fixed order every time: record SIDPP, SICP, slow rate and pressure; calculate kill mud weight; calculate initial circulating pressure as SCR plus SIDPP; calculate final circulating pressure as initial circulating pressure multiplied by kill mud weight divided by original mud weight; then build the schedule. Check each intermediate number against a rough mental estimate before moving on.
Describing the driller's first actions on a kick as shutting in the well immediately without first stopping the pumps, or continuing to circulate while shutting in.
Candidates conflate the hard shut-in and soft shut-in procedures and lose the sequence. They also forget that the correct first action is to stop rotating and stop the pumps, then close the BOP, then check pressures and record them, and that the soft shut-in opens the choke before closing the BOP and then closes the choke.
What to do instead
Memorise the hard shut-in as a numbered sequence: stop pumps, stop rotation, pick up off bottom if required by the procedure, close the BOP, open the choke line valve, observe and record SIDPP and SICP, then confirm the pit gain. State clearly that the well is shut in before any pressure reading is meaningful, and distinguish hard from soft shut-in by which valve is open when the BOP closes.
Confusing the annular preventer with the pipe rams when describing which element seals on which part of the drill string, or stating that the blind rams can be closed on drill pipe.
Candidates learn BOP stacks as a list and do not attach each element to its function. They also miss that variable bore rams cover a range of pipe sizes while fixed rams do not, and that shear rams and blind rams are for closing an open hole, not for sealing around pipe.
What to do instead
Build a table linking each BOP element to what it seals on and when it is used: annular for any shape including open hole and for stripping, pipe rams for a specific pipe size, variable bore rams for a range, blind rams for open hole, shear rams to cut pipe before closing. Answer BOP questions by naming the element, the object it seals against, and the operation it supports.
Calculating the influx height or the kill mud weight without first correcting for the difference between true vertical depth and measured depth on a deviated well.
Candidates use the along-hole depth printed on the tally because it is the number most visible in the stem, and forget that all pressure calculations use true vertical depth. On vertical wells the two are equal, so the habit is never corrected until a deviated example appears.
What to do instead
Before any pressure or gradient calculation, extract the true vertical depth from the survey data given and write it beside the measured depth. If only measured depth is supplied, state that the well is assumed vertical or that TVD must be obtained from the survey, and use TVD in every hydrostatic and kill calculation.
Treating the slow circulating pressure as the pressure to hold on the choke throughout the kill, rather than adjusting the choke to follow the calculated pressure schedule as kill mud is pumped.
Candidates learn the final circulating pressure as a single number and then hold it from the start, or they hold the initial circulating pressure and never reduce it. They also do not distinguish the two-phase schedule (kill mud to the bit, then to surface) from a single constant pressure.
What to do instead
Describe the kill as two phases: while kill mud travels down the drill string, the casing pressure is held on the schedule from initial to final circulating pressure as the heavier mud fills the string; once kill mud reaches the bit, the circulating pressure is held constant at the final circulating pressure while the choke is adjusted to keep drill pipe pressure steady. State which pressure is held and which is allowed to vary in each phase.
Answering well control questions on the choke manifold and choke types without distinguishing a positive choke from an adjustable choke, or stating that the choke is used to control the influx volume.
Candidates mix up the choke's role (controlling casing pressure and therefore bottom hole pressure) with the pit gain or influx volume, and they do not link fixed versus adjustable chokes to the ability to change pressure during a kill. This produces answers that sound right but invert cause and effect.
What to do instead
State the choke's function as maintaining bottom hole pressure by controlling casing pressure while circulating, and note that an adjustable choke allows the pressure to be changed during the kill whereas a positive choke holds a fixed restriction. When a question asks about influx volume, answer in terms of pit gain and shut-in pressures, not choke setting.
Failing to recognise a kick indicator other than a pit gain, such as a flow check showing continued flow with pumps off, a drilling break, or a change in pump pressure and stroke count.
Candidates rehearse pit gain as the primary indicator and then miss questions built around secondary indicators. They also do not connect a drilling break or a sudden increase in rate of penetration to the need for a flow check, so they describe continuing to drill.
What to do instead
List the kick indicators by category: primary (pit gain, flow with pumps off), secondary (drilling break, increase in penetration rate, change in pump pressure or strokes, gas or oil shows, change in mud properties). For each, state the immediate action, which for a drilling break is to stop drilling, stop the pumps, and perform a flow check before continuing.
Describing well control actions after a kick without addressing the risk of the influx migrating when the well is shut in and not circulating, or without stating the pressure limit that triggers action.
Candidates focus on the kill calculation and treat the shut-in period as static. They do not mention that gas percolates upward and raises both drill pipe and casing pressure, and they cannot state the casing pressure limit at which the well must be bled or circulated.
What to do instead
In any shut-in scenario, state that pressures are monitored and recorded at regular intervals, that migration is detected by rising drill pipe and casing pressure with no change in pit volume, and that the well is bled or the kill started before casing pressure approaches the rated working pressure of the BOP stack or casing seat. Give the limit as the lower of the two ratings and name it explicitly.