Since the 1970’s the UK Continental Shelf (UKCS) has produced large amounts of oil and gas, with the latest figures (NSTA, 2022) amounting to around 46.4 billion barrels of oil equivalent (boe) during the ~40 years of production. The UK’s oil & gas industry, based in and around Scotland’s territorial waters has been at the forefront of developing the energy landscape we see today in the UK and around the world.
The changing landscape of the North Sea
UKCS production peaked in the 2000’s but has since gone into decline, with older fields depleted and imports becoming more economically viable, the boom seen in the late 1990’s won’t be seen again. The industry is now focussing on the safe abandonment and decommissioning of oil and gas wells and is moving towards new revenue streams such as the repurposing of wells and renewable energy.
Image by Elliott Day from Pixabay.
The challenges of decommissioning wells
Well abandonments may seem like the final chapter in the story of a well, but in reality, they involve a meticulous and regulated process to ensure environmental safety and compliance. Regulatory bodies have stringent requirements to prevent any adverse impact on the surrounding ecosystem. Factors such as well integrity, reservoir pressure, and geological conditions play a pivotal role in determining the approach to abandonment.
The North Sea Transition Authority (NSTA), previously known as the Oil and Gas Authority is the regulator of all activity on the UKCS and is focussed on driving the North Sea energy transition as well as maintaining the economic value of current production assets. The NSTA also regulates the decommissioning and repurposing of the UKCS infrastructure, which is a major industrial challenge for operators.
Once a field or well has been exhausted, all other options have been explored, and no economic potential is proven the process of decommissioning will begin. This stage of oil and gas projects is a key part of the lifecycle of operations in the North Sea and is meticulously planned and executed by the whole supply chain from appraisal to execution, often taking decades to complete.
Documented Abandoned wells in the North Sea
Industry working together to solve problems
Safe and reliable well plug and abandonment (P&A) activities, a major aspect of decommissioning present more of a challenge with higher relative value than the visible infrastructure. There are an estimated 150-200 wells per year that will be decommissioned in the next decade in the North Sea, with spending forecast to increase until 2025 before innovations in the sector bring costs down. (OEUK, 2024).
According to Oil & Gas UK’s 2023 Decommissioning Insight report, well decommissioning activity accounts for just over half (51%) of the full cost of a project. Within the oil and gas industry, there is a growing consensus that operators and the supply chain should increase knowledge sharing to allow for more efficiency and cost savings, organisations such as Decom Mission are working to facilitate these conversations.
UKCS decommissioning expenditure by year
(Image: Figure 2, P.12, Decommissioning Insight 2023 report, OEUK)
Solutions for successful and cost-effective well plug and abandonment
GeoScience have been undertaking geomechanical studies on North Sea wells since the late 1990’s and has processed data from over 8500 offset wells. We have an extensive archive of field specific geomechanical models our clients can use as a basis for decommissioning studies, providing a cost-effective resource to aid the design of their P&A programs.
Decommissioning studies derived from existing geomechanical models can capture production history from reservoir pressure data, lithology through the overburden, losses depths, wireline data for cap-rock integrity and details of wellbore construction.
In fields not previously worked, an in situ stress assessment can be undertaken and a geomechanical model built deriving in situ stress and rock mechanical properties from log data in selected nearby offsets. The minimum horizontal stress can then be calibrated to known losses / no losses points observed in the offset wells. The minimum safe abandonment depth will be determined for barrier placement to isolate any potential flow and selected next to a cap rock of adequate thickness with a minimum horizontal stress greater than the expected pressure at that depth.
North Sea well abandonments represent a critical phase in the lifecycle of offshore wells. By embracing technological advancements, stringent regulatory frameworks, commitment to environmental preservation and collaboration, professionals in the oil and gas industry can navigate the complexities of well abandonments with efficiency and expertise. As we continue to evolve our practices, the legacy we leave in the North Sea will be one of responsible stewardship and sustainable energy production.
To find out more about how we can work with your team to help provide solutions for the plug and abandonment of wells, please get in touch with our geomechanics team today.
References
North Sea Transition Authority; UK Oil and Gas Reserves and Resources report: https://www.nstauthority.co.uk/media/8394/reserves-and-resources-2022.pdf
North Sea Transition Authority: https://www.nstauthority.co.uk/regulatory-information/decommissioning-and-repurposing/
OEUK Decommission Insights Report 2023: https://oeuk.org.uk/product/decommissioning-insight-2023/
Research Gate, Permanent Caprock Abandonment P&A Assessment Incorporating Rock Mechanics Analysis: Petrophysics Perspective: https://www.researchgate.net/publication/329243502_Permanent_Caprock_Abandonment_PA_Assessment_Incorporating_Rock_Mechanics_Analysis_Petrophysics_Perspective
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