Case Study

Decommissioning: concrete leg and underdeck clearance and preparation (EPC)



Fixed Platform, North Sea

The Dunlin Alpha platform was installed in 1977, comprising a concrete gravity base structure (CGBS), supporting a steel topsides deck, and production facilities.

Dunlin Alpha ceased production mid-2015 and planning and execution for the decommissioning of the installation was completed over the following years with the topside finally removed in early 2022.

In order to prepare the platform for topside removal AquaTerra Group provided Engineering, Procurement, and Construction (EPC) to prepare the concrete legs for the later removal of the platform topside by heavy lift vessel.

AquaTerra Group was the main contractor responsible for provision of all necessary engineering, fabrication, planning, project management and construction services.

Key Summary
  • Full EPC contract for internal and external leg clearance
  • Project integrated engineering, procurement, and construction services
  • Multi-discipline FEED study for the internal clearance of all legs within the proposed cut line
  • EPC contract for all external and internal leg clearance activities
  • Internal clearance of all structural items, piping, electrical, HVAC and lift systems
  • External leg clearance of escape to sea ladders, spider deck walkways and pipework systems
The Challenge

Two fundamental challenges underpinned this scope: space constraints and personnel limitations.

All internal work areas fell under the confined space hazardous areas classification. The worksites themselves were highly congested, presenting a challenge for any lifting operation. Throughout the scope, the platform continued to operate with a fully manned crew, posing significant Personnel on Board (PoB) limitations.

With no existing precedent for the clearance of the legs, standard operating procedures were not suitable for some of the destruct works. Additionally, live cabling and pipework were integrated into the platform's legs, some of which needed maintenance until the final abandonment stage.


Role, Co.

The Solution

AquaTerra Group provided a dedicated onshore project management team, with a dedicated focal point to ensure continuous client support, scope management, and vendor coordination.

Integrating design and execution, AquaTerra Group streamlined internal feasibility studies, design processes, procurement, and installation, optimising efficiency.

Adaptability was crucial for this scope. AquaTerra Group deployed multi-skilled offshore teams, equipped with diverse skills, spearheading a construction-led engineering approach.

QuikDeck® access systems were strategically placed within the project's four legs. This facilitated safe and efficient access during both destructive phases and subsequent installations.

All lifting and rigging equipment was supplied, inspected and maintained by AquaTerra Group. This commitment ensured operational safety and overall project efficiency.

The Result

In providing a full turnkey service, AquaTerra group limited the number of project interfaces required for the operator, resulting in an efficient, streamlined delivery.

The integration of construction-led engineering into the project led to significant cost savings by delivering fit for purpose engineering packages for the execution phase.

AquaTerra Group's wealth of experience in working with concrete legs and hazardous confined spaces translated into an environment of heightened safety and productivity. Our expertise resulted in zero Lost Time Incidents (LTIs).

Through adeptly tackling challenges with innovative solutions, Aquaterra Group achieved a safe and successful execution of this complex EPC project.

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