Over 2,000 oil and gas wells are scheduled for decommissioning in the North Sea over the next decade. Decommissioning offshore infrastructure is a messy bureaucratic process, a complex technical task and doesn’t exactly rate highly in the court of public opinion.

At an average cost of 7.8 million GBP per well, deconstructing these old structures is a massive market opportunity. There’s also a lot of subsea steel slated for removal. Steel that has spent decades becoming one with its surrounding natural environment.

These subsea structures hold potential value far greater than the market value of decommissioning. Returning them to nature as already-established artificial reefs enhances the marine environment. So, why isn’t this happening?

Decommissioning off-shore fixed-platforms

Before discussing the merits or demerits of repurposing subsea steel from offshore energy assets, we need to first establish what the decommissioning process entails.

Decommissioning is an asset’s end-of-life phase when it is shut down either because it has maxed out its productive life, or for economic, socio-political or other unforeseen issues. It is a reverse engineering of sorts. This complex and challenging deconstruction process typically includes shutting down operations and securing the asset, as well as removing and/or repurposing the physical structure.

While there are various types of offshore well structures in situ in the North Sea, those slated for decommissioning tend to be of a fixed-platform type. A fixed platform sits atop a steel truss structure called a jacket that is literally fixed to the seafloor with deep, steel support pilings. This underwater steel jacket supports the pipes that deliver oil and gas up to the platform; it is a complex network of beams and, hence, offers a high surface-area-to-volume ratio (ideal for ecosystem enhancement as a growing medium for organisms!).

Figure 1. Fixed platform

Certainly, when it comes to applying circular economy principles and sustainable practices in construction, decommissioning seems to subscribe to the polar opposite (and antiquated) cradle-to-grave paradigm. Notably, for offshore oil and gas and the environmental and political sensitivities therein, decommissioning is vilified. There is an increased push to repurpose hydrocarbon assets into those for renewable energy (i.e. offshore wind). However, the more ambitious of these plans are a decade in the making and subject to a wide range of scrutiny and approvals.

Biological systems engineering principles applied to decommissioning

The interface of the built and natural environments is a fascinating place of focus. Every single built asset has some degree of interface with the surrounding environment, typically revolving around resource use and waste management.

The half-a-century-old subsea steel, once operations are properly shut down and secured, does not consume nor produce. What it does is provide a habitat for aquatic life. Over time, artificial reefs, which are effectively what these steel structures naturally become, hold the potential to host the same community structure and be as productive as natural reefs.

Fixed platform structures have been shown to dramatically increase populations of some species such as red snapper, and even host endangered cold-water corals. When attached to offshore oil and gas infrastructure, some species, including starfish and mussels, even experience higher growth rates and have been recorded to reach their upper-known limits.

Engineering solutions are at their best when taking cues from nature. For a subsea steel structure to be integrated into the natural environment, becoming a part of it, the decommissioning solution becomes obvious.

Rigs to reefs: the reefing of old offshore oil and gas assets

Initiatives to officially repurpose sub-sea steel jacket structures of old oil and gas assets into artificial reefs to enhance marine biodiversity do exist. There are three engineering approaches:

1. Tow-and-place,
2. Topple-in-place, and
3. Partial removal

Figure 2. Reefing methods

As shown in the figure, reefing via the tow-and-place and topple-in-place removal methods can use underwater explosives to break the below-the-seafloor jacket legs. Whereas the topple-in-place and partial removal reefing methods can rely on the mechanical severing of the steel legs either above or below the seafloor.

The tow-and-place method is in the name: once detached by explosives, it is towed to a designated reefing site (unlike the other two methods, where the reefing site is the structure’s current location). The partial removal method has an option of placing either the partial or full steel jacket on the seafloor as reef material. Benefits of partial removals include reduced trauma and habitat loss and higher reef profiles.

From bad PR to bad policy

Why aren’t fixed platforms being reefed in the North Sea?

In spite of a flourishing decommissioning market and research and initiatives in favor of reefing old offshore oil and gas structures, it’s been over two decades since an oil company attempted to do so in the North Sea.

A PR debacle revolving around the infamous Shell-owned Brent Spar holds the answer. The Brent Spar was constructed in the mid-1990s. A floating oil storage facility in UK waters, with a tanker-loading facility, it was slated for decommissioning following the completion of a pipeline, which rendered it useless. The British government alongside a consortium of international partners and scientists advised disposing of the Brent Spar in the ocean, claiming negligible environmental impact.

Well, it got ugly from there. Greenpeace got involved, slaughtering the plan with unsubstantiated (and false) claims that several thousand tons of oil remained on the structure. The pressure was so strong that the decision to leave the Brent Spar in the ocean was reversed following formal government objections. Greenpeace was supported by “influential companies in the offshore construction sector who stood to make money from onshore dismantling.”

It was a hot mess all around. While Shell can be held to task for a staggering lack of environmental awareness, Greenpeace’s smear campaign was, at least in part, propaganda that later proved untrue. For example, evidence ultimately revealed impressive biodiversity growing on the submerged surfaces of the Brent Spar.

The unintended consequence is that European governance around the UK Continental Shelf (UKCS) seems to have been scared off of the decommissioning-as-reefing concept altogether. This manifested in the OSPAR Decision 98/3 on the disposal of disused offshore installations, which requires the full removal of oil platforms, including disposal onshore, at the end of their productive lives.

Engineers as alchemists can turn subsea steel into gold (with policy and popular support)

Decommissioning is an essential lifecycle stage for offshore hydrocarbon assets known more so for its financial, environmental and safety risks than for its opportunity.

It’s easy for offshore decommissioning projects to get a bad rap, but the alchemy of progressive engineering solutions holds the potential to transform steel into gold. In this instance, a most valuable transformation would occur in the repurposing of decommissioned subsea structures into artificial reefs.

When special interests are kept at bay, biological engineering principles rise to the surface offering extractive industries a way to give back.

This article is also published on The Weld Hotwire. illuminem Voices is a democratic space presenting the thoughts and opinions of leading Sustainability & Energy writers, their opinions do not necessarily represent those of illuminem.