Pit Gain at 2,450 m: Confirming a Kick and Building a Kill Sheet
At 06:40 the well is being drilled at 2,450 m TVD (vertical) with 1.22 sg water-based mud when return flow at the shakers increases and the active pit total rises by 4.5 m³ in eight minutes. The driller stops the top drive, picks up off bottom and closes the annular preventer. After five minutes the pressures stabilise at SIDPP 38 bar and SICP 52 bar. The slow circulating pressure recorded at the planned kill rate of 30 spm is 34 bar. The kill sheet on the console is eight days old and was prepared at 1,800 m. The choke manifold is lined up through the poor boy degasser, the mud pumps are running at 30 spm, and the suction pit has 40 minutes of kill mud capacity. The toolpusher is in the office on a call and the company man is asking for a written programme before any pump is started.
1. Confirm whether this is a kick, then calculate the kill mud weight and the initial and final circulating pressures at 30 spm. State your assumptions and rounding rule.
Read the worked answer
A 4.5 m³ pit gain with increased return flow, followed by a stable SIDPP of 38 bar, confirms an influx. The well is shut in and pressure is trapped on both gauges, so this is not a false gain from mud transfer or pit settling.
Kill mud weight: KMW = MW + SIDPP ÷ (0.0981 × TVD) KMW = 1.22 + 38 ÷ (0.0981 × 2,450) KMW = 1.22 + 38 ÷ 240.3 = 1.22 + 0.158 = 1.378 sg
Round up to 1.38 sg. Never round down, because the extra 0.002 sg gives a small safety margin without approaching the shoe fracture limit.
Initial circulating pressure: ICP = SIDPP + slow circulating pressure = 38 + 34 = 72 bar at 30 spm.
Final circulating pressure: FCP = SCR × (KMW ÷ MW) = 34 × (1.38 ÷ 1.22) = 38.5 bar at 30 spm.
Assumptions: the well is vertical so TVD equals the measured depth at the bit; the SIDPP is fully stabilised; there is no trapped pressure from hurried closure; the 34 bar SCR is valid for 30 spm and 1.22 sg mud. If the SCR is doubtful, a slow pump rate test can be taken, but it must not delay the kill.
2. List the actions you would take before and during the first circulation. Explain why the eight-day-old kill sheet does not justify waiting for the company man's written programme.
Read the worked answer
Before pumping:
- Record SIDPP, SICP, pit gain, time and choke position; start a pressure log every 5–10 minutes and every 100 strokes.
- Notify the toolpusher and company man, raise the alarm and brief the crew on roles: choke operator, pump operator, pit watcher, floor hand.
- Physically verify the choke manifold, degasser, flare or vent line and pump line-up; confirm the choke can be adjusted smoothly and the casing pressure gauge is readable.
- Mix 1.38 sg kill mud and confirm sufficient volume and mixing rate.
- Calculate the pressure schedule, but be ready to use the driller's method if the kill mud is not yet ready.
During the first circulation:
- Bring the pump to 30 spm while holding casing pressure constant with the choke.
- Confirm the pressure at kill rate is close to the calculated 72 bar; if not, investigate before proceeding.
- Hold the casing pressure schedule, monitor pit gain, pump pressure, gas and shoe pressure, and do not open the choke rapidly to 'let gas out'.
The old kill sheet does not justify delay. It gives a starting point, but the SIDPP, SICP and SCR are current measurements taken at this depth. Well control is immediate: waiting for a written programme while an influx migrates increases casing pressure and the risk of an underground blowout.
3. SICP minus SIDPP is 14 bar. What can cause that difference, and what would you do if SICP rose to 65 bar while the pump was at 30 spm and SIDPP stayed steady?
Read the worked answer
The 14 bar difference is the pressure exerted by the influx in the annulus plus any trapped pressure created during closure. It does not, by itself, identify the influx as gas or liquid; a gas influx usually shows a larger and growing difference as it expands, while a small liquid influx may show little change. The value alone is not a reliable influx-type test.
If SICP rises to 65 bar while pump rate and SIDPP are steady, gas is migrating or expanding faster than the pressure schedule accounts for. Do not stop the pump and do not dump pressure quickly. Maintain the scheduled casing pressure by opening the choke in small, controlled increments, watching SIDPP, pit gain and pump pressure after each adjustment. If the pumps must be stopped, keep the well shut in and use a controlled bleed or lubrication procedure to keep casing pressure within the shoe limit while the influx is handled.
Monitor the shoe: at 1,900 m TVD, a 1.56 sg EMW limit corresponds to a finite casing pressure margin. If casing pressure approaches that limit, increase mud weight only under a written plan, and consider circulating faster or using the wait-and-weight method if the current schedule cannot control migration.