Case Study

Tarsiut Caisson Removal

Client

ConocoPhillips Canada

Location

Herschel Island, Yukon, Canada

Year

2017

Scope of Support

LPMS supported the project management of the Tarsiut caisson removal campaign, including planning and preparation, subcontractor and vendor coordination, logistics, cost and schedule control, change management, execution support, demobilization and project close-out.

The work included coordinating the refloat preparation and marine spread, managing procurement and variation-order requirements for mooring and anchoring equipment, maintaining commercial and schedule visibility, and supporting the interfaces between the client, marine contractors, diving contractor, logistics providers and specialist vendors.

LPMS Role

Project Management

Project Phase

Planning, mobilization, execution, demobilization and close-out

Duration of Involvement

2017 execution campaign, with close-out continuing into early 2018

Tarsiut concrete caissons during the 2017 removal campaign in the Beaufort Sea.

01 — Project Context

Project Context

Tarsiut was a caisson-retained artificial drilling island built in the early 1980s in the Beaufort Sea, one of the first structures of its kind used for Arctic exploratory drilling. Gulf Canada drilled two wells there in 1981 and 1982, with as many as 131 people on site at a time during operations. The structure consisted of four watertight concrete caissons floated into position and infilled with dredged sand to withstand severe Arctic storms and ice loading.

After the platform was decommissioned in 1984, the four caissons, each weighing approximately 5,500 metric tons, were towed to Thetis Bay off Herschel Island, Yukon, where they remained resting on the seabed for roughly three decades. In 2017, ConocoPhillips Canada undertook a project to responsibly remove the caissons entirely, refloat them, and transport them to Mexico for environmentally sound recycling, consistent with the company's commitment to managing its historic operations responsibly and its relationship with the local Inuvialuit community.

A 54,000-metric-ton semisubmersible heavy-lift vessel was mobilized to the remote Arctic site. The refloating operation itself took roughly two weeks: pumping out decades of accumulated seawater, working the caissons loose from the seafloor, and using sonar and diver surveys to confirm the seabed and structures were clear of debris before staging the caissons for load-out.

LPMS provided project management and project controls support on the engagement, coordinating logistics and heavy marine transport planning for the caisson refloating and relocation, and helping maintain schedule and cost visibility across a project executed in one of the most remote and operationally demanding locations in the world.

Marine operations supporting the refloating of the Tarsiut concrete caissons.

02 — Execution Constraints

Key Challenges

Remote Arctic execution with limited local services and complex transport routes through Edmonton and Inuvik.
A narrow two-to-three-month seasonal operating window, worsening metocean conditions, frequent fog and ice-related constraints.
Multiple parallel workstreams, including regulatory approval, early mobilization, vessel readiness, caisson refloating, debris recovery, heavy-lift transport and disposal planning.
Four concrete caissons of approximately 5,500 tonnes each, resting on the seabed for roughly three decades.
Scope development during preparation, including additional procurement, custom mooring brackets and anchoring equipment.
Communication and supervision challenges between separate execution spreads during offshore operations.

Tarsiut caissons prepared for heavy-lift transport from Herschel Island.

03 — LPMS Approach

LPMS Approach

Allowed an extended planning and preparation period to resolve logistics, contractor compliance, mobilization routes and execution requirements before offshore work began.
Worked backward from the disposal solution and maintained contingency options while key approvals and contracts progressed in parallel.
Used a detailed planning schedule, defined decision deadlines and regular risk review to maintain a clear line of sight across the campaign.
Visited and vetted critical subcontractors before engagement, including review of diving personnel, equipment and procedures.
Structured commercial changes through signed variation orders before procurement or rental commitments were made.
Planned mobilization and demobilization around the limitations of Arctic trucking, marine access and seasonal operating windows.

04 — Outcomes

Outcomes

All four caissons were refloated and temporarily moored between July 22 and July 26, 2017.
The caissons were loaded onto the heavy-lift vessel at Herschel Island and transported to Ensenada, with marine operations completed on August 23, 2017.
Equipment reached the mobilization location in accordance with the project schedule, and demobilization was executed as planned.
Additional scope and procurement requirements were documented and commercially managed through variation orders.
No HSE incidents involved project personnel or subcontractors during execution, apart from a pre-execution stop-work intervention that was corrected before work continued.
The project closed with a materially stronger gross-margin result than anticipated at bid stage, supported by additional revenue and disciplined commercial management.

Heavy-lift transport of the four Tarsiut concrete caissons.

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