March 19, 2024 | Susan Napier-Sewell

An Assumption Can Lead You to Being All Wet (Bad Day)


IOGP (International Organization of Oil & Gas Producers) shares a Well Control Incident Lesson Sharing report recounting a breakdown in communication, preparation and monitoring, process control — a plan was based on an assumption.

Let’s track this incident: Importantly, through the findings, we identify that the overarching project plan was erroneously based on the expectation, albeit assumption, that the reservoir was depleted.

What happened to cause the plan to be based on an assumption?
In a field subjected to water flooding, when drilling through shales and expecting to enter a depleted reservoir, gas readings suddenly increased. Subsequently, the mud weight was increased, the well was shut-in, and the drill string became stuck when the hole collapsed during kill operations. Water-flood break-through risks were not communicated to the drill crew, and the drill crew failed to adequately monitor the well during connections. The loss of well control, hole, and drill string was due to poor communication and well-monitoring.

  • Drilling 8″1/2 x 9″1/2 hole with 1.30SG mud weight (MW) at 2248m – this mud density is used to drill the top section shales for borehole stability purpose
  • Crossed an identified sands layer which was expected to be sub-hydrostatic (0.5SG)
  • Observed a connection gas reading up to 60% + pack off tendency.
  • Increased mud weight by step to 1.35SG but gas readings were still high
  • Decided to shut the well in and observed pressure in the well SIDP 400 psi – SICP 510 psi
  • A Gain of +/- 10m3 was estimated later (by postmortem analysis of the previous pipe connection and pump-off logs)
  • Performed Driller’s Method and killed the well by displacing 1.51 SG kill mud
  • Open hole collapsed during circulation with the consequence of string getting stuck and kick zone isolated

What went wrong? 
The reservoir was expected to be depleted. This part of the field was artificially over-pressurized by a water injector well. This was not identified during the well preparation phase. and the risk was not transmitted to the drilling teams. Lack of crew vigilance. Poor well monitoring during DP connections. The high connection gas observed at surface were the result of a crude contamination in the mud system. Significant gain volumes were taken during the previous pipe connections without being detected.

Corrective actions and recommendations 
-The incident was shared with drilling personnel and used for training purposes.

-Shared the experience and emphasized to reinforce the well preparation process with a rigorous risk identification: the hazard related to a continuous injection in a mature field to be emphasized.

-Reinforce well monitoring. Specifically, during pipe connections.

-Review mapping of injection on the field.

Circumstances can crop up anywhere at any time if proper sequence and procedures are not planned and followed. We encourage you to learn and use the TapRooT® System to find and fix problems. Attend one of our courses. We offer a basic 2-Day Course and an advanced 5-Day Course. You may also contact us about having a course at your site.

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