Collision between wells while drilling leads to blow-out

• The well was located on an onshore site where 17 wells had been drilled already on 3 different clusters. The drilling rig had successfully drilled 4 previous wells.
• The operations were performed in SIMOPS (Simultaneous Drilling and Production operations) mode as several wells of the cluster were producing.
• The 26" Conductor Pipe had been pre-driven. The 23" phase was drilled. The hole was plugged back due to 18-5/8" surface casing cementing failure.
• A southward extension was made to the existing cellar to accommodate the re-spud. The new well centre was located at 2.5m from the plugged back well.
• The 26" CP was driven to 130m by the rig.
• The CP was cleaned out and a gyro dropped, giving 6° of inclination.
• The CP was not as vertical as requested in the drilling program. However the azimuth was considered good when compared to the initial plan. No well re-planning was considered. Decision was made to drill ahead.
• The 23" phase was drilled to 600m taking MWD surveys.
• At 600m, an MWD alarm flagged, indicating metal proximity. Personnel on the rig suspected interference with the abandoned branch of another well where a fish was left in hole. Decision was made to continue drilling ahead and pass below the fish.
• An obstruction was tagged few meters deeper.
• The rig called the base. The Operator's team and the directional drilling company rep confirmed that the intersection was with the abandoned fish. Decision was made to side-track the well on the low side to nudge away from the fish.
• The BHA was picked up 3 metres, tool-face oriented downwards and an attempt was made to pass under the supposed fish in sliding mode.
• There was a shift change on the rig floor. After drilling few metres, high torque and vibration were experienced. Drilling continued, although shallow geological formations were known to be easy to drill. A strong mud flow occurred through the rotary table. The BHA had accidentally drilled through the 13-3/8" and 9-5/8" casing and punched the 5-1/2'' tubing of a producing well located in a cluster 125m away from the drilling location. This well had not been included in the directional drilling company data base used for the anti-collision calculations.

What Went Wrong?:

The main causes of the incident were as follows:

1. Use of an incomplete data base that did not include all the wells in vicinity of the drilling location, resulting in an under-estimation of the potential collision risks.
2. Company rules not observed (requesting double check of directional drilling company anti-collision calculation with independent software)
3. Revision of the directional drilling programme should have been made once CP inclination was recorded.
4. Once a problem was detected, decision was made to drill ahead without proper risk assessment and analysis.
5. A closer supervision should have been in place at the rig-floor during a non routine operation. Stop work authority was not exercised.

Corrective Actions and Recommendations:

No assumption should be made regarding intersection when preparing a directional drilling programme. All wells should be present on the spider plot.

Personnel on the rig site should carry out a thorough follow up of the well trajectory and cross-check with the base.

Any deviation from the original programme should be followed by the issue of a revised programme communicated to and understood by all parties involved on the rig and at the base.

Drilling into an obstruction should not be considered as acceptable, whether it is an identified object or not: magnetic interference should trigger a change of programme and increased vigilance. Drilling should be stopped at the first indication of contact with an anomaly.

safety alert number: 265
IOGP Well Control Incident Lesson Sharing http://safetyzone.iogp.org/

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