Losses at the shoe while the kill is still in progress
The 8½ in hole is at 14,200 ft MD / 13,000 ft TVD when a 14 bbl gain is taken. Mud weight is 13.2 ppg and shut-in pressures stabilise at SIDPP 520 psi and SICP 760 psi. The 9⅝ in shoe is at 9,800 ft TVD with an LOT of 15.2 ppg equivalent. Slow circulating rate is 30 spm at 650 psi. The kill mud is calculated and the kill is started at 30 spm with an ICP of 1,170 psi and an FCP of 690 psi. Two hours in, with the top of the gas approaching the shoe, the choke is at 640 psi to stay on schedule, the returns at the shakers fall to about 40%, the active pit drops 9 bbl in 12 minutes, and the gas units at the shakers stay high.
1. Diagnose what is happening in the well. Show the numbers that support your diagnosis and say why this situation is more dangerous than an ordinary kick.
Read the worked answer
Kill mud weight = 13.2 + 520 ÷ (0.052 × 13,000) = 13.2 + 0.77 = 13.97 ppg, so 14.0 ppg was used.
Pressure at the shoe at this moment ≈ hydrostatic of kill mud at the shoe + choke pressure = 14.0 × 0.052 × 9,800 + 640 = 7,134 + 640 ≈ 7,774 psi. The LOT is 15.2 × 0.052 × 9,800 = 7,746 psi. The shoe is at, or a few psi beyond, its leak-off point.
Diagnosis: the well is taking a kick at 13,000 ft and losing fluid into a formation at 9,800 ft at the same time. The gas is expanding as it comes up, so the choke pressure needed to hold bottom-hole pressure rises, and that extra pressure is landing on the weakest point in the open hole. The 9 bbl pit drop with only 40% returns confirms a real loss, not a choke washout or a shaker problem - check both anyway before acting.
This is worse than a normal kick because continued losses drop the annular fluid level, which drops bottom-hole pressure and lets more reservoir fluid in, while the loss zone takes the fluid you are pumping. Unchecked, it becomes an underground blowout: gas migrating into a shallower permeable zone, possibly outside the casing.
2. Give the sequence of actions and identify what you are protecting first.
Read the worked answer
Priority is the shoe. A fractured shoe turns a controllable kick into an uncontrolled crossflow that cannot be fixed from surface.
- Verify the loss: confirm the pit drop against the stroke counter, check the flow line and shakers, and confirm the choke is not washing out. A false loss reading leads to the wrong action.
- Do not stop the pumps abruptly. Keep circulating; stopping drops the annular friction and the well unloads.
- Reduce the choke pressure only to the shoe limit - hold casing pressure at the MAASP for the mud in the hole, (15.2 − 14.0) × 0.052 × 9,800 ≈ 611 psi, and accept a small underbalance at the bottom rather than breaking the formation down. That may let a little more influx in; that is the cheaper problem.
- Reduce the pump rate in steps to reduce annular friction, adjusting the choke to keep the bottom-hole pressure as close to the pore pressure as the shoe allows.
- Spot an LCM pill across the shoe and pump it, then re-establish the schedule.
- Keep the annulus full to the extent the loss allows, and record every volume in and out.
- Log pressures, rates and volumes each 10–15 minutes and keep the operator informed.
3. The LCM pill does not cure the loss and the pit is now down 35 bbl with the well still flowing at the shakers. What are your remaining options and how do you rank them?
Read the worked answer
You are now managing a well that is flowing and losing simultaneously; the objective shifts from killing it to keeping it contained and preventing the loss zone from becoming the flow path.
Ranked options:
- Continue to hold the shoe at MAASP while pumping the heaviest LCM/ loss-seal pill you have, and keep the hole full with whatever volume the loss takes. This is the only option that still kills the well, so it comes first.
- Reduce the circulating rate further to cut annular friction and lower the shoe pressure without dropping bottom-hole pressure more than necessary.
- Set a barite plug or a cement plug across the loss zone. This is slower and can be dangerous if the well is flowing while you do it, but it caps the loss zone so the annulus can be re-filled and the kill completed.
- Bullhead the loss zone only if the string is plugged or the bit is off bottom and there is no other circulation path, and only with the shoe pressure limit clearly defined.
- Evacuate and monitor if the loss cannot be contained and gas is reaching surface uncontrolled - an underground blowout is a well-control event you contain from a distance, not from the rig floor.
Do not increase the mud weight to chase the flowing well while the shoe is broken; that accelerates the loss and the crossflow. If you must stop pumping, close in and record SIDPP and SICP before doing anything else.