CCS Legacy Well Risk Workshop, Edinburgh

The IEAGHG, in collaboration with Heriot-Watt University (HWU) and Scottish Carbon Capture and Storage (SCCS), hosted a CCS Legacy Well Risk Workshop at the Edinburgh Climate Change Institute on Thursday 24th and Friday 25th July. The workshop was organised as a result of an ongoing IEAGHG research study conducted by HWU and SCCS, with some initial findings shared and discussed during the event. However, the agenda extended well beyond the study, incorporating contributions from government, regulators, operators, and research institutions. The diverse representation of over 50 participants reflected this broad engagement.

This workshop also built upon discussions and presentations from the June 2023 IEAGHG Risk Management Network meeting, also hosted by HWU, which focused on legacy well risks in CCS projects.
The event spanned a day and a half. After a welcome from Aaron Cahill (HWU), Nikki Clarke (IEAGHG), and Gillian White (SCCS), the first keynote was delivered by Freya Marks from the UK’s Department of Energy Security and Net Zero (DESNZ). On the second day, Margaret Copland from the North Sea Transition Authority (NSTA) provided the keynote address. Although both speakers were UK-based, the workshop had clear international relevance.

Key Themes from the Welcome and Keynotes

Legacy Wells Context: Aaron Cahill set the scene by highlighting the global scale of legacy wells—potentially over 10 million—and shared fieldwork insights on leakage from hydrocarbon wells and implications for CCUS.

UK CCUS Overview: Freya Marks outlined the UK’s CCUS landscape, noting that legacy wells can be both an asset (as a source of subsurface data) and a liability (due to added risk, reduced capacity, delays, and increased costs).

Regulatory Perspective: Margaret Copland emphasised that every well within a potential storage site must be assessed to ensure there is ’no significant risk’ of leakage or harm to the environment or human health—going beyond the traditional oil and gas ALARP (As Low As Reasonably Practicable) standard. She stressed that CO₂ must either be kept away from problematic wells or those wells must be remediated—an achievable but potentially costly and complex task.
A key takeaway was that well screening should be one of the first steps in any CCS project. While plug and abandonment (P&A) practices may meet decommissioning standards, they may not suffice for CO₂ storage. The success of early UK projects could set a precedent, making public trust and engagement essential.

Workshop Sessions and Highlights

The workshop featured three sessions, comprising 10 talks and three panel discussions:

Session 1: Policy, Regulatory and Industry Context

Zoe Sayer (NSTA): Provided an overview of UKCS regulatory requirements, noting over 1,400 legacy wells in current CCS licences.
Rodrigo Oropeza (Storegga): Shared insights from screening over 650 legacy wells. He emphasised the importance of early screening, data quality, and team alignment, cautioning against underestimating the scale of the task.

David Buchmiller (DNV): Offered a perspective from the assurance sector, highlighting the need for alignment on risk frameworks. He noted that external stakeholders often prefer independent assessments and that DNV is working on a CCS Wells Technology Roadmap with NSTA and NEP.

Session 2: Unpacking Risk Factors

HWU & SCCS Team (Aaron Cahill, Benjamin Pullen, Andrew Cavanah, Gillian White): Presented findings from the IEAGHG study. A follow-up poll (led by Iain de-Jonge-Anderson) revealed that environmental factors, leakage rate estimates, and reputational/societal risks were seen as most critical, while natural mitigation and seepage analogues were considered less important.

Benjamin Emmel & Bastien Dupuy (SINTEF), Presented screening workflows from the LEGACY project and a monitoring technique deploying CSEM at the Svelvik field laboratory.

Owain Tucker (Shell): Reinforced the principle that ‘there is no capacity without containment’, sharing field examples and practical considerations for remediation.

Session 3: Innovation in Risk Modelling and Decision Tools

Hari Ramachandran, Iain de Jonge-Anderson, Aaron Cahill, Benjamin Pullen: Introduced QwellRate, an open-source, physics-based model for rapid CO₂ leakage assessment from legacy wells.

Clement Joulin (Net Zero Geosystems) & Brian Willis (Astrimar): Simulated well 32/4-1 at the Smeaheia site, using a risk-based, ALARP-compatible framework to estimate leakage probabilities and magnitudes.

Paul Gupta (ExxonMobil): Presented flow modelling and quantitative risk assessments from the Gulf Coast, focusing on brine migration and the potential for wellbore collapse to act as a barrier.
In the final panel, there was broad agreement on the value of field research to calibrate modelling results. Some participants called for clearer guidance on acceptable leak probabilities, though regulators indicated that specific thresholds are unlikely to be defined.

Networking and Acknowledgements

Networking was enhanced by the beautiful atrium at the Edinburgh Climate Change Institute, which hosted refreshment breaks and a drinks reception. Dinner was held at the Scotch Whisky Society, where delegates enjoyed a single malt alongside traditional haggis—all set against the backdrop of Edinburgh’s historic charm.
Special thanks go to the hosts from HWU and SCCS, particularly Aaron Cahill, Benjamin Pullen, and Sophie Cox (HWU), and Gillian White and Andrew Cavanah (SCCS), for facilitating a successful and impactful event.