IWCF Level 2 Drilling common mistakes
IWCF Level 2 Drilling · Understand the traps and how to avoid them.
When asked to identify the shut-in procedure after a kick, the candidate lists steps in the wrong order, for example closing the annular preventer before opening the choke line or forgetting to record shut-in drill pipe pressure (SIDPP) and shut-in casing pressure (SICP) before starting to circulate.
Candidates memorise the steps as a list without understanding the purpose of each step: isolating the well, then recording pressures before any circulation changes the pressure reading. Under exam pressure they recall the steps in the order they were first taught rather than the logical sequence.
What to do instead
Learn the shut-in sequence as a cause-and-effect chain: stop rotation and pumps, raise the string, close the BOP, open the choke line, then record SIDPP and SICP. Practise writing the sequence from memory and explain why each step comes before the next. On the exam, check that pressures are recorded before any circulation step.
The candidate confuses kill weight mud with the current mud weight when calculating the mud weight required to balance formation pressure, or uses SIDPP instead of SIDPP plus the original mud hydrostatic in the formula.
The formula Kill Mud Weight = Current Mud Weight + (SIDPP ÷ (0.052 × TVD)) is memorised as symbols without understanding that SIDPP represents the overbalance in pressure terms that must be converted to mud weight. Candidates also mix up TVD and MD.
What to do instead
Work through the derivation: SIDPP is the pressure the formation exerts above the current mud hydrostatic, so it must be converted to an equivalent mud weight using true vertical depth. Practise at least ten calculations with different units (psi, bar, kPa) and check that the answer is always higher than the current mud weight when there is a kick.
When describing the slow circulation rate (SCR) and kill rate, the candidate states that the kill rate is the normal drilling rate or gives a pressure that is not adjusted for the kill rate.
Candidates conflate the slow circulation rate used for well control with the normal drilling circulation rate, and they forget that the circulating pressure at kill rate must be measured and recorded before the kill sheet is completed.
What to do instead
Learn that the kill rate is a reduced pump rate, typically one-third to one-half of normal, chosen so that the annular pressure loss is manageable. Memorise that the initial circulating pressure (ICP) is SIDPP plus the slow circulating pressure, and that the final circulating pressure (FCP) is the slow circulating pressure multiplied by (kill mud weight ÷ original mud weight). Practise calculating both and check that ICP is greater than FCP when the kill mud is heavier.
The candidate cannot distinguish between the choke line pressure loss and the annular pressure loss when completing the kill sheet, and applies the wrong correction to the drill pipe pressure schedule.
The kill sheet has several pressure terms (SIDPP, SICP, SCR, choke line friction, annular friction) and candidates memorise the sheet layout without understanding which pressures act where in the wellbore.
What to do instead
Draw a simple wellbore diagram and label where each pressure acts: SIDPP at the drill pipe, SICP at the casing, choke line friction in the choke line, annular friction in the annulus. Learn that the choke line friction is added to the casing pressure while bringing the pump to kill rate, and that the annular friction is already included in the slow circulating pressure. Practise completing a kill sheet from a given data set.
When asked about the function of the BOP stack, the candidate describes only the annular preventer and omits the pipe rams, blind rams, and shear rams, or states that the annular preventer is used to shear pipe.
Candidates learn the BOP as a single item rather than as a stack of components with different functions, and they confuse the sealing capability of the annular preventer with the mechanical action of the shear ram.
What to do instead
Build a component table: annular preventer (seals around any shape, allows movement), pipe rams (seal around a specific pipe size), blind rams (seal empty hole), shear rams (cut pipe and seal). Learn which component is used for which operation, such as hanging off, stripping, or emergency disconnect. Test yourself by naming the correct ram for five different scenarios.
The candidate misidentifies the primary well control barrier and lists the BOP as the primary barrier rather than the hydrostatic pressure of the mud column.
The BOP is visually prominent and candidates associate well control with the BOP, missing the concept that the mud column is the primary barrier and the BOP is the secondary barrier.
What to do instead
Learn the barrier philosophy: primary barrier is the fluid column (mud hydrostatic), secondary barrier is the mechanical equipment (BOP, casing, wellhead). Practise classifying barriers in different scenarios, such as drilling, tripping, and intervention. On the exam, check whether the question asks for primary or secondary before answering.
In the well intervention pressure control domain, the candidate states that the wireline grease injection head is used to control pressure during logging, or confuses the function of the stuffing box with the grease injection head.
The wireline pressure control equipment is a stack of similar-looking items and candidates memorise the names without linking each item to its pressure-control function.
What to do instead
Learn the wireline pressure control stack from bottom to top: wireline valve (BOP), grease injection head, stuffing box, and lubricator. Learn that the grease injection head seals around the wire by injecting grease, the stuffing box provides a primary seal, and the wireline valve is the secondary barrier. Draw the stack and label the function of each item.
When calculating the maximum allowable surface pressure for a well intervention, the candidate uses the formation fracture pressure at the casing shoe without converting it to surface pressure, or uses the wrong depth.
The candidate memorises the formula but does not understand that the fracture pressure at the shoe must be converted to an equivalent surface pressure by subtracting the hydrostatic pressure of the fluid column above the shoe.
What to do instead
Learn the relationship: Maximum Allowable Surface Pressure = Fracture Pressure at Shoe − Hydrostatic Pressure of the fluid column (using TVD to the shoe). Practise with different fluid densities and shoe depths. Check that the answer is lower than the fracture pressure and that the depth used is the true vertical depth of the shoe, not the measured depth.
The candidate describes the procedure for lubricating the well (bleeding gas) incorrectly, for example bleeding gas before allowing the gas to migrate or not recording the pressure after each bleed.
Candidates learn the term 'lubricate' but do not understand the principle of allowing gas to migrate to the surface, then bleeding a volume of gas while maintaining bottomhole pressure constant.
What to do instead
Learn the lubricate-and-bleed procedure step by step: allow gas to migrate (pressure rises), bleed a measured volume of gas from the choke, record the pressure, and repeat until gas is removed. Understand that the bottomhole pressure must remain constant, so the volume bled must be replaced by an equivalent hydrostatic pressure. Practise a worked example with a gas volume and pressure increase.
The candidate answers questions about the purpose of the kill line and choke line by stating that both are used for circulation, without distinguishing that the kill line is used to pump kill mud into the well and the choke line is used to control the outflow.
The two lines are physically similar and candidates memorise them as a pair without understanding their different roles in the well control circuit.
What to do instead
Trace the flow path: kill mud is pumped down the drill pipe, up the annulus, out through the choke line to the choke manifold, and the kill line is an alternative path to the drill pipe or a backup. Learn which line is used for which operation and why the choke line must be open before the BOP is closed. Draw the circuit and label the direction of flow.