Map of Tern-2 well location; Source: Santos

Santos seeks all-clear for plug and abandon ops at Australian field

Australian energy player Santos has submitted an environment plan (EP) to the country’s offshore regulator, covering decommissioning activities at a field off the coast of Australia.

Map of Tern-2 well location; Source: Santos

Within its environment plan, handed over to the National Offshore Petroleum Safety and Environmental Management Authority (NOPSEMA), Santos proposed to plug and abandon (P&A) the Tern-2 wellhead located within the Tern field of retention lease license WA-27-R in the Bonaparte Basin within Commonwealth waters, approximately 300 km WSW of Darwin, in water depths of approximately 83 m.

According to the company, all wells in the Tern field have been permanently plugged and abandoned except Tern-2, which is currently classified as temporarily abandoned. As a result, the focus in the firm’s EP is on installing and verifying additional well barriers to supplement the existing system and support the removal of the wellhead and well infrastructure at the seabed.

Furthermore, the P&A campaign is said to be predominantly concerned with the removal of equipment to eliminate future hazards to the environment or other uses of the area as best as practicable. However, a carbon steel drilling template and remnants of a cement patio buried below the mudline will not be retrieved. Instead, these will remain in situ in perpetuity. If leaving the wellhead in situ is necessary, Santos underlines that the residual risk to other marine users and the environment is perceived to be very low.

While the Australian firm elaborates that the P&A campaign will be conducted using a light well intervention vessel (LWIV), it also points out that it is anticipated that a support vessel will not be required during P&A activities, however, provision for a single support vessel is accounted for throughout the EP.

In addition, a remotely operated vehicle (ROV) will also be used to carry out activities such as corrosion cap cleaning and an ‘as left’ ROV survey that will be conducted after the P&A activity while helicopters and a support vessel may be used to transfer crew and equipment to and from vessels/LWIV and assist in emergencies as required.

Regarding the activities for the P&A of Tern-2, the firm explains that these may entail corrosion cap removal, including marine growth removal from wellhead infrastructure; well integrity evaluation such as wireline drift run, wireline cement bond logging of wellbore casing; and permanent isolation of the reservoir like abandonment plug setting.

There is also the wellhead recovery, covering wellhead severance and recovery, wellhead leave in-situ contingency if full recovery is not feasible; vessel operations such as LWIV and contingent support vessel; ROV activities, including well site surveys; and helicopter activities for emergencies.

Even though the activity duration is expected to take up to approximately ten days of continuous operations, 40 days of activity duration has been considered to allow for unforeseen delays. Once started, operations will be 24 hours per day, seven days per week, but the exact timing and duration of the P&A activities are subject to LWIV availability, regulatory and business approvals, and metocean conditions.

Santos is working on bringing new projects online. To this end, the firm has made progress at its Barossa gas field development offshore Australia with the recent completion of a 262-kilometer gas export pipeline.

Related Article

With hull, topsides, and turret and mooring system construction 98%, 94%, and 96% complete, respectively, the FPSO BW Opal, which will be deployed at the field, is progressing per the existing schedule for the first gas in the first half of 2025.