Well integrity study for decommissioning

We performed a technical post well investigation of the Client’s planning and execution performance relating to plug and abandonment of a subsea exploration well.

The Client’s exploration well had been drilled and abandonment operations commenced.

After having plugged and cut the 9 5/8” and 13 3/8” casing strings, small gas bubbles were rising out of the well when the BOP was lifted off the wellhead. The BOP was re-connected and a series of remedial actions followed involving multiples of squeeze cementing, removal and re-setting of cement plugs, setting new bridge plug and one barite squeeze. The cement plug located close to seabed was finally tested and held pressure. The wellhead was then cut and the well topped up with cement.

We were contacted to give advice on further action to rectify the situation, then followed with the task of conducting a technical investigation.

What we did

Data gathering and interviews

AGR’s Well Integrity Specialist conducted data collection and interviews, focusing on how the Client’s Drilling organization had planned and executed the operations, with particular attention to compliance with Client’s and regulator’s requirements to abandonment activities and how changes were managed.

Technical and operational analysis

Information and knowledge from events that occurred prior to the abandonment activities, such as kick in 12 ¼” hole, higher pore pressure and higher bottom hole temperature than forecasted, caused no apparent changes in the planned activities relating to 9-5/8” casing cementing and verification, and the abandonment program relating to casing cutting and plug depths. The most likely leak-path was through the 9 5/8” casing cement (poor bonding) and into the well above the 9 5/8” casing stub.

Compliance verification

The planning and execution of the P&A operations were compliant with local regulations, partially compliant with Client’s procedures and non-compliant with NORSOK D-010 Well Integrity Standard.