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Lynden Duthie

AGR completes challenging multi-well abandonment campaign in Timor Sea

AGR’s team in Perth was appointed to plan and execute a complicated permanent multi-well abandonment campaign, covering seven wells in the Puffin Oil Field in the Timor Sea, 250km off the coast of Northern Australia.

The Challenges

A long list of complex challenges to overcome

The campaign, for Sinopec Oil & Gas Australia (SOGA), involved abandoning two production subsea wells and five suspended subsea wells. All except one of the five suspended wells required the blowout preventer (BOP) stack to be run in order to pull the 9 5/8” slip and seal assembly, thereby mitigating the risk of trapped annular gas. 

A further complication was the mixture of wellhead types in the field. Three of the suspended wells had H4 type profile wellheads, while the remaining had Cameron hub type profiles. This meant that the BOP required a connector change-out during the campaign.

There were logistical challenges to overcome too. The field location was 700km from Darwin (the port of mobilisation,) and a 4,000km journey by road to Perth, which was the main oil and gas equipment and services hub.

A large amount of equipment was also needed for this project. The two production wells had dual bore trees, meaning a dual bore riser system had to be used. This added significant additional equipment for the project and made operations more complex.

The fact that the production wells were designed as gas lift wells also created difficulties. Approximately 1,600PSI gas lift was known to be present in the annulus, which required flaring off.

To add to the challenges, numerous drift runs on one of the production wells failed to reach the target depth due to corroded or broken tubing. This meant contingency work was needed before successful plug and abandonment (P&A) could be achieved.

AGR Solution

The campaign called for abandonment specialists operating in a tight knit team

Essential to a successful outcome in this complex set of circumstances was the quality of the project team. AGR assembled a group of highly experienced P&A specialists, organising them into a tight knit team that possessed the skills needed to overcome every obstacle. This team sequenced the P&A operations to enable the BOP connector change-out to be performed off rig.

Due to the presence of annulus gas and the possibility of hydrocarbons in the annulus, a decision was made to mobilise a bleed-off package and additional surge tanks. This proved critical to the campaign’s success since large volumes of oil were found in the annulus of both production wells.

The Outcome

Despite all that could have gone wrong, team quality won through

  • All seven wells were successfully plugged and abandoned, with the final cost within 1% of Authorisation for Expenditure (AFE). Considering the tubing issues encountered on Puffin 7 and the disruption that could easily have occurred with a less experienced team, this was an outstanding result for the client.
  • When the tubing deterioration was identified on Puffin 7 AGR specialists promptly devised alternative solutions and put robust procedures and equipment in place.
  • The project was a safely and efficiently delivered P&A success, meeting all technical, logistical, environmental and regulatory objectives. With the potential for so much to go wrong, the outcome has set the standard for tough P&A projects.
  • The effectiveness of highly-experienced P&A teams working closely with clients to give them a clear understanding of what is happening throughout the campaign won the day.

‘Two separate vessels were contracted to complete the offshore operations and the execution of work on both vessels was undertaken seamlessly and with the highest regard for safety. This is directly related to the detail and effort by AGR during the onshore, planning and preparation phase and as a result significant time was saved offshore and the project came in approximately 15% under budget.’ – Puffin Decommissioning General Manager, SINOPEC Oil & Gas Australia (Puffin)

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