Assessing all options

Emma Gordon

October 30, 2017

As the North Sea enters the decommissioning era, should complete removal remain the default option? And what is the impact of the process on North Sea ecosystems? Emma Gordon reports. 

The oil and gas industry must address its knowledge gap about the sea life that lives in and around its installations and associated infrastructure, if we are to properly understand the consequences of decommissioning.

That’s according to Andrew Guerin, University of Newcastle research associate, who spoke at a Society for Underwater Technology-hosted session at SPE Offshore Europe 2017.

After four decades of production, North Sea decommissioning work has started in earnest and is set to ramp up in the short- to medium-term.

Currently, operators are under a legal obligation to remove all platforms and associated structures from the seabed, with the option to apply for a derogation in certain cases (steel jackets weighing more than 10,000-tonne, gravity-based concrete structures…).

Yet, Guerin says, these structures have become colonized and typically develop highly productive ecosystems including invertebrates, fish, seabirds and other predators. Are there ecological benefits to leaving the installations in place? If removed, what happens to these communities?

A bird hunts fish around an offshore platform. Photo from iStock.

The problem in answering that question, he explains, is that a lot of existing knowledge is at a “fairly superficial” level. While we know what species live on and around installations, we don’t know a lot about their ecology, or indeed how they fit into the wider North Sea marine ecosystem, he says.

“Decommissioning will affect biological systems over different timescales and areas, and it’s really quite hard to forecast what the impact of decommissioning will be.”

Guerin says there would be little effect on those organisms living and growing on the platform over the short term if the structures remained. However, he said: “It’s worth bearing in mind that at some point any infrastructure [still in place] may eventually fail… there may be consequences we may not see immediately.”

Partial removal would likely see persistence of sea life on what is left behind, with some loss of habitat and redistribution of certain species.

While complete removal, including anything growing on the platform, would lead to the redistribution of species elsewhere, with reef associated fish — those only found on reefs or similar structures, such as the Wolffish — potentially lost entirely. It would have the benefit that “once everything is removed, there is no scope for further impacts in the future,” however.

The impact of partial or complete removal on marine mammals is even more uncertain: “We don’t know how these animals do or don’t interact with the structures at the moment. It’s very difficult to figure out what happens if we remove [them].”

Knowledge of the effect on the wider marine ecosystem is even more porous, particularly if there’s a network effect created by structures, acting as islands.

There is work underway to understand these issues, including the Insite Program (OE: February 2017).

This research initiative, involving scientists and researchers from across the UK and Europe, is working to assess the impact of man-made structures on marine life, both individually and as a network. The program started in 2015, and are set to run up until the end of this year.

Three of the eight projects focus specifically on connectivity and are run by the Centre for Environment Fisheries and Aquaculture Science (CEFAS), Lowestoft, UK; IMARES, Texel, Netherlands; and the University of Edinburgh’s School of Geoscience, Scotland.

Another initiative underway is a Natural Environment Research Council (NERC)-funded joint science industry project, led by the National Oceanography Centre (NOC).

NOC scientist, Daniel Jones, said at the Offshore Europe event that the one-year project — with partners including BP and Shell — started in April, and looks at developing “best practice guidelines” for effective monitoring using the latest generation autonomous systems to provide low-cost, high quality, repeat assessment.

Jones has been involved, too, with the Scientific and Environmental ROV Partnership using Existing Industrial Technology (Serpent) Project, which uses underwater vehicles for deep-sea research during stand-by periods, augmenting these findings with data collected as part of routine offshore work, as well as from existing environmental assessments.

“There is a large requirement for marine monitoring, in all cases [of decommissioning] environmental impact assessments will be needed, and the derogation cases will need more extensive monitoring, potentially for the entirety of their lifetime.”

Yet, Jones says, there is no standard approach for assessing the ecological role of structures for these environmental assessments, and current assessments have not led to clear conclusions.

In an environment where infrastructure such as cables and wires can make survey operations complex, and with the considerable scale of decommissioning the industry faces — around 500 installations in the UK Continental Shelf alone — Jones says that autonomous systems can be a “transformative technology,” capable of providing a more standardized approach for decommissioning monitoring.

From gliders and observatories, to automated underwater vehicles (AUVs), the project will look at the current approach and how it can be adapted for decommissioning.

Jones adds that there are a number of relevant applications, including acoustic and visual mapping looking at, for instance, pipelines and cuttings piles on the seafloor; visual assessments to, for example, detect and classify marine life with speed and efficiency, and using sensors on AUVs to assess water quality and carry out wide area pollution assessments.

The ability to augment findings with historical information is crucial, Jones said, adding: “There is a wide variety of existing data … it would be a shame to lose that, so we have to work out how we can mesh the two together.” 

Further Reading:

Plenty of fish in the sea
North Sea decommissioning is finally happening and it means some difficult questions are starting to be asked about what should be left behind and what might benefit sea life. Elaine Maslin explores the details.