As we navigate the complex landscape of energy transition, a promising solution is emerging from an often overlooked source: our existing oil and gas infrastructure. While the need to move away from fossil fuels is clear, the path forward must be both workable and sustainable—technically, economically, and environmentally.

At Heriot-Watt University's Global Research Institute for "net zero and beyond," iNetz+, we're exploring how repurposing oil and gas wells for geothermal energy could play a crucial role in Scotland and the world's renewable energy future.

The geothermal potential of the North Sea

The North Sea, long known for its oil and gas reserves, harbors another valuable resource—heat. Geothermal energy, an almost inexhaustible renewable resource, has been used for power generation worldwide since the early 20th century. Now, as we look to decommission oil and gas wells, we have an unprecedented opportunity to tap into this clean energy source.

Repurposing existing infrastructure for geothermal energy offers a multitude of advantages. It's a cost-effective approach that avoids the environmental impact and substantial expense of drilling new wells. After decades of production, these reservoirs are well understood, significantly reducing the risk of drilling new wells that potentially fail—an important factor in guaranteeing the economic viability of such projects.

This strategy can potentially extend the life of existing assets and provide new opportunities for the existing skilled workforce, easing the transition to a renewable energy future.

From hydrocarbons to heat

The transition from hydrocarbon extraction to geothermal energy production involves several innovative approaches. Open loop systems directly produce hot formation water for geothermal energy. This method has been successfully tested in various parts of the world, including the U.S., China, or Colombia. In the late phases of oil and gas production, when water content in produced fluids increases, the energy in these brines can increasingly be harnessed for geothermal power.

Closed loop systems offer another promising avenue. In this approach, fluid circulates through a single well in a closed circuit, absorbing heat from the surrounding rock. While this method prevents issues like mineral scaling, it may have limited heat exchange capacity. However, looking globally, innovations like using long horizontal wells, similar to those used in unconventional gas production, could significantly increase the contact area between the well and the working fluid, enhancing efficiency.

Where natural fluid flow is insufficient, enhanced geothermal systems (EGS) can be employed. This technique uses hydrofracturing to create pathways to access geothermal fluids farther from the well, potentially tapping into higher temperatures at greater depths. EGS could be particularly useful in supporting both open and closed loop completions, expanding the potential of geothermal energy extraction.

Challenges and opportunities

While the potential is exciting, repurposing oil and gas infrastructure for geothermal energy is not without challenges. Current regulations allow only a short time frame between cessation of hydrocarbon production and well abandonment. We need to work with policymakers to create a regulatory framework that facilitates this transition, addressing concerns about potential hazards and leakage while enabling the development of this promising technology.

Beyond regulatory hurdles, we also face significant technical challenges. The technical aspects of geothermal production differ significantly from traditional hydrocarbon extraction. For example, geothermal systems require a detailed understanding of heat exchange, small-scale heterogeneities, and the impact of fractures and faults. This shift demands new expertise and a reimagining of how we view and utilize these underground resources.

Alongside technical considerations, economic viability remains a key factor in the transition to geothermal energy. The efficiency of geothermal energy extraction, especially from low-temperature resources like those found in many North Sea reservoirs, continues to advance. Hot geothermal fluids can be converted to electricity using a closed binary cycle, which uses the heat from produced well water to vaporize a secondary fluid with a lower boiling point.

While this process is well-established in various setups, including geothermal applications, ongoing innovations are enhancing its performance. As these technologies progress and global energy dynamics shift towards renewables, the economic case for geothermal energy grows increasingly compelling.

Finally, we must consider the human element in this transition. The potential for workforce transition adds another layer of complexity and opportunity to the geothermal revolution.

Net zero and beyond

At Heriot-Watt University, we're leveraging our expertise in both traditional energy systems and renewable technologies to address these challenges head-on. Our new Global Research Institute for Net Zero is at the forefront of research into sustainable energy solutions. Our work on repurposing oil and gas infrastructure for geothermal energy is just one aspect of our broader mission to facilitate a just and effective transition to net zero emissions.

We recognize that while we must move away from oil and gas, these industries have played a crucial role in Scotland's economy and have fostered invaluable expertise. Our goal is to build on this foundation, repurposing not just physical infrastructure but also knowledge and skills for a sustainable future.

The transition to renewable energy is not a single solution but a mosaic of interconnected approaches. Repurposing oil and gas infrastructure for geothermal energy represents an innovative piece of this puzzle. To realize its potential, we need collaboration between industry, academia, and government.

We invite energy companies, policymakers, and fellow researchers to join us in exploring this opportunity. Whether it's through joint research projects, policy discussions, or industry partnerships, there's a role for everyone in shaping this potential geothermal revolution in the North Sea and beyond.

At iNetz+, we're committed to driving this research forward. If you're interested in learning more about our work on geothermal energy or other net-zero transition projects, we encourage you to reach out. Together, we can turn the challenges of energy transition into opportunities for innovation, sustainability, and economic growth.