Project summary

Well plug, abandonment and remediation program.

Service categories

• Well engineering & operations
• Decommissioning
• Project delivery

Project overview

Throughout 2020-21 our team were engaged by ReNu Energy to design and execute a final plug, abandonment and remediation program of the 4,200m deep partially-decommissioned Habanero 3 & 4 geothermal wells. These wells both exhibited a legacy slow gas weep, and were required by the SA regulator to be attended to prior to relinquishment of the license.

These wells experienced extensive post-drilling disruption, with Habanero 3 blowing out in 2009. Furthermore, despite long-term monitoring data being available on current conditions of the well, incomplete reporting left information gaps in the previously attempted plug and abandonment program.

Wellsafe services

The abandonment design and execution processes were outlined in a comprehensive program underpinned by achieving several critical success factors. To best satisfy these factors, we underwent a thorough decision analysis process to review and select the most suitable sub-contractors to execute the program efficiently, effectively and safely. We then provided continual in-field supervision with clear communication, advice and instruction from a supporting remote engineering team.

The high-level work program for Habanero 4 included:

• Drilling through and replacing the old top cement plug on the casing shoe within 9 5/8″ casing.
• Perforating 9 5/8″ casing without breaching the 13 3/8″ casing at 442 mRT and 390 mRT.
• Setting bridge plug at 443.7 mRT and retainer at 439.5 to execute a successful annular resin squeeze.
• Placement of cement plug inside the 9 5/8″ casing adjacent and above the resin squeeze.
• Placement of a surface cement plug after several weeks of monitoring.

The high-level work program for Habanero 3 included:

• Setting resin plug from inside 9 5/8″ casing.
• Perforating through 9 5/8″ casing without breaching the 13 3/8″ casing.
• Executing a successful resin squeeze in the 9 5/8″ to 13 3/8″ annulus.
• Cutting through 7″ casing to gain circulation with 9 5/8″ annulus.
• Setting cement plug in 9 5/8″ casing to inside 7″ casing and swell packer BHA.
• Cutting and removing 7″ casing from above the cement plug top.
• Cutting 9 5/8″ casing free above the cement plug top.
• Filling 9 5/8″ annulus and well-bore with barite to provide a sound base for placement of a balanced cement plug.
• Setting cement plug from 46 mRT to near surface.

From our review, we chose EasternWell as the primary and rig contractor, and Halliburton for wireline and cementing services. A “well on paper” exercise was held with all involved parties, including the regulator, to answer any questions and queries ahead of finalising the technical work programs.
An icebreaker was also held infield ahead of commencing the well intervention activities with Wellsafe, Halliburton and EasternWell crew members. Daily safety meetings were held before any activities that deviated from the original program were performed. Gas and radioactivity levels were always monitored. A COVID-19 Management Plan was put in place, including sign-offs for all personnel entering site and temperature checks prior to entry.

The varying teams worked cohesively together under our supervision and guidance, and adapted to the uncertain well conditions. Ultimately, the goals of the program were successfully completed.

Performance outcome

The main highlights across the plug and abandonment of Habanero 3 & 4 were:

• Collaborative brainstorming potential causes of well behaviour using the extensive experience of the team to develop sound and pragmatic solutions.
• Technical success with setting plugs and performing squeezes, with both the client and regulator satisfied with the condition to meet abandonment requirements despite facing several challenges.
• The multiple contractors involved in the operation on site were managed effectively by Wellsafe supervision to deliver a seamless project and excellent result.
• In both wells the micro annulus leak paths were successfully resin squeezed above the gas source enabling the final decommissioning of the wells and approval to proceed with site rehabilitation.