Europe's Geothermal Transition: Why Repurposing Oil Wells Isn't as Simple as It Sounds

Repurposing Hydrocarbon Wells for Geothermal Applications

Insights from Our Interview with Christi on EGS, Storage, and Europe’s Energy Transition

Christi is a Geothermal Resource Engineer and PhD Researcher, specializing in deep geothermal systems, closed-loop systems, well repurposing (especially converting old oil/gas wells for geothermal use), Enhanced Geothermal Systems (EGS), and Deep Borehole Heat Exchangers (DBHE).

What if the thousands of oil and gas wells scattered across Europe could become the backbone of the geothermal transition?

In our recent interview with Christi, a leading researcher involved in the TRANSGEO project, we explored the technical, economic, and regulatory realities of repurposing hydrocarbon wells for geothermal applications ,

particularly for Enhanced Geothermal Systems (EGS), thermal storage, and district heating integration.

From case studies like Groß Schönebeck to regional analysis in Lausitz, Christi offered a grounded and technical perspective on what works   and what doesn’t  in well repurposing.

Let’s break it down.

1. Well Selection: Not Every Abandoned Well Qualifies

Repurposing an oil or gas well is not as simple as plugging in a heat exchanger and turning on the pumps. According to Christi, the workflow begins with rigorous screening.

Critical Selection Criteria

In Germany’s case, three factors are fundamental:

Subsurface temperature, Without sufficient temperature, the economics collapse.

Wellbore diameter, The bottom-hole casing must be greater than 7 inches. Wells with less than 7” casing diameter are typically disqualified because modification for liner casing production becomes technically limiting.

Well age, Wells older than 30 years are generally avoided due to integrity risks.

Additionally, partially abandoned or fully abandoned wells often face regulatory or structural challenges that make conversion impractical.

 “Out of 1,000 abandoned wells, you might find none that are viable,” Christi emphasized.

The idea that thousands of wells automatically translate into geothermal potential is misleading. Viability is rare , and highly site-specific.

2. Technical Modifications: Integrity is Everything

The biggest technical hurdles revolve around:

Well completion modifications

Long-term well integrity

Casing–reservoir fluid interaction

Hydraulic stimulation performance

Germany currently applies five geothermal technologies:

Shallow to medium-depth ,Borehole Heat Exchangers

Hydrothermal systems

Enhanced Geothermal Systems (EGS) (still under development)

Aquifer Thermal Energy Storage (ATES) (research stage)

Borehole Thermal Energy Storage (BTES) (research stage)

While shallow systems are mature, deeper EGS and storage systems remain under research and demonstration.

3. Lessons from Groß Schönebeck: EGS in Practice

At Groß Schönebeck, a former gas exploratory well  E GrSk 3/90 , was successfully converted into an EGS injection well. This stands as a field example of how repurposing can work when geological conditions align.

Using:

3D geological modeling

Reservoir simulation

Cross-flow testing between injection and production wells

Engineers designed multi-stage fracture concepts for fracture-dominated EGS systems.

However, Christi was clear:

Repurposing does not automatically improve heat extraction or well longevity.

Its purpose is to add value to existing infrastructure rather than abandon it.

Performance largely depends on the effectiveness of hydraulic stimulation and fracture geometry.

In short: repurposing is an economic optimization strategy , not a performance miracle.

4. The Economic Reality: Where the 50–60% Savings Come From

The primary economic advantage is obvious:

Drilling has already been done.

Avoiding new drilling can reduce capital expenditure by 50–60%, making projects financially attractive , but only under the right conditions.

Key Cost Drivers

Heating distribution infrastructure

Integration into district heating systems

Electricity price benchmarks (~12 cents)

Heating energy prices (~30 cents)

Government offtake structures (e.g., affordability constraints in Indonesia)

Christi estimates the “impact advantage” of repurposing at around 50% compared to greenfield geothermal development.

But without district heating demand or viable offtake pricing, economics quickly become strained.

5. Storage & Hybrid Systems: ATES and BTES Potential

Beyond power and heat production, storage systems are emerging as a promising use case.

ATES and BTES technologies are particularly attractive in:

Northern Europe

Canada

These regions have:

Strong seasonal heating and cooling demand

Existing wells with bottom casing diameters greater than 7 inches

District heating infrastructure

However, BTES requires multiple wells in a network for effective storage functionality. Single-well applications are limited.

In former oil and gas regions, these systems could help:

Balance seasonal energy demand

Stabilize district heating networks

Lower heating costs

But again , infrastructure integration is key.

6. Regulatory Complexity: A Cross-Border Challenge

Within Central Europe, regulations differ widely. Each country:

Protects well integrity differently

Has distinct liability frameworks

Applies unique permitting procedures

Liability for legacy wells remains one of the biggest non-technical barriers.

Christi stressed the need for:

Minimum integrity standards

Transferable technical criteria

A consortium-based approach

Scalable frameworks adaptable at local levels

While subsurface physics may be similar across borders, governance is not.

7. TRANSGEO’s Core Lesson: No Universal Workflow

One of the most important insights from the TRANSGEO pilot feasibility studies is this:

Reservoir characteristics are not transferable.

Engineering workflows cannot simply be copied from one site to another.

Each project requires:

Site-specific modeling

Demand-side evaluation

At least two economically viable geothermal reservoirs

At least two possible energy applications within a single well

District heating demand must already exist — or be realistically deployable.

Without demand, even technically viable wells fail economically.

8. Future Outlook: Massive Opportunity, Tough Reality

Europe has thousands of oil and gas wells.

The opportunity is immense.

But the real question is:

How many countries are willing to commit those wells to geothermal conversion?

Scaling depends on:

Policy commitment

Regulatory harmonization

District heating expansion

Financial risk-sharing models

Emerging technologies like closed-loop systems could further accelerate adoption. Christi noted that closed-loop systems are effective , but currently limited to around 100 kW, primarily for heating rather than electricity generation.

Supercritical or superhot rock concepts, requiring two to three wells, could push boundaries further , though these remain technologically and economically complex.

Final Reflection: From Abandonment to Asset

Repurposing hydrocarbon wells is not a silver bullet. It does not automatically increase productivity or extend well life.

What it does is transform stranded infrastructure into potential geothermal assets.

But viability is rare. Out of 1,000 abandoned wells, none may qualify.

The transition depends not just on geology — but on policy, economics, district heating networks, and national commitment.

The geothermal transition will not be powered by theory alone.

It will be powered by selective, strategic, economically viable conversions.

And as Christi’s insights reveal, the future of repurposed wells lies at the intersection of engineering realism and political will.

At Alphaxioms, we continue to explore how oil and gas repurposing can unlock geothermal value , not through assumptions, but through rigorous technical assessment and economic discipline.

Repurposing Hydrocarbon Wells for Geothermal Applications

Insights from Our Interview with Christi on EGS, Storage, and Europe’s Energy Transition

What if the thousands of oil and gas wells scattered across Europe could become the backbone of the geothermal transition?

In our recent interview with Christi, a leading researcher involved in the TRANSGEO project, we explored the technical, economic, and regulatory realities of repurposing hydrocarbon wells for geothermal applications ,

particularly for Enhanced Geothermal Systems (EGS), thermal storage, and district heating integration.

From case studies like Groß Schönebeck to regional analysis in Lausitz, Christi offered a grounded and technical perspective on what works   and what doesn’t  in well repurposing.

Let’s break it down.

1. Well Selection: Not Every Abandoned Well Qualifies

Repurposing an oil or gas well is not as simple as plugging in a heat exchanger and turning on the pumps. According to Christi, the workflow begins with rigorous screening.

Critical Selection Criteria

In Germany’s case, three factors are fundamental:

Subsurface temperature, Without sufficient temperature, the economics collapse.

Wellbore diameter, The bottom-hole casing must be greater than 7 inches. Wells with less than 7” casing diameter are typically disqualified because modification for liner casing production becomes technically limiting.

Well age, Wells older than 30 years are generally avoided due to integrity risks.

Additionally, partially abandoned or fully abandoned wells often face regulatory or structural challenges that make conversion impractical.

 “Out of 1,000 abandoned wells, you might find none that are viable,” Christi emphasized.

The idea that thousands of wells automatically translate into geothermal potential is misleading. Viability is rare , and highly site-specific.

2. Technical Modifications: Integrity is Everything

The biggest technical hurdles revolve around:

Well completion modifications

Long-term well integrity

Casing–reservoir fluid interaction

Hydraulic stimulation performance

Germany currently applies five geothermal technologies:

Shallow to medium-depth ,Borehole Heat Exchangers

Hydrothermal systems

Enhanced Geothermal Systems (EGS) (still under development)

Aquifer Thermal Energy Storage (ATES) (research stage)

Borehole Thermal Energy Storage (BTES) (research stage)

While shallow systems are mature, deeper EGS and storage systems remain under research and demonstration.

3. Lessons from Groß Schönebeck: EGS in Practice

At Groß Schönebeck, a former gas exploratory well  E GrSk 3/90 , was successfully converted into an EGS injection well. This stands as a field example of how repurposing can work when geological conditions align.

Using:

3D geological modeling

Reservoir simulation

Cross-flow testing between injection and production wells

Engineers designed multi-stage fracture concepts for fracture-dominated EGS systems.

However, Christi was clear:

Repurposing does not automatically improve heat extraction or well longevity.

Its purpose is to add value to existing infrastructure rather than abandon it.

Performance largely depends on the effectiveness of hydraulic stimulation and fracture geometry.

In short: repurposing is an economic optimization strategy , not a performance miracle.

4. The Economic Reality: Where the 50–60% Savings Come From

The primary economic advantage is obvious:

Drilling has already been done.

Avoiding new drilling can reduce capital expenditure by 50–60%, making projects financially attractive , but only under the right conditions.

Key Cost Drivers

Heating distribution infrastructure

Integration into district heating systems

Electricity price benchmarks (~30 cents)

Heating energy prices (~12 cents)

Government offtake structures (e.g., affordability constraints in Indonesia)

Christi estimates the “impact advantage” of repurposing at around 50% compared to greenfield geothermal development.

But without district heating demand or viable offtake pricing, economics quickly become strained.

5. Storage & Hybrid Systems: ATES and BTES Potential

Beyond power and heat production, storage systems are emerging as a promising use case.

ATES and BTES technologies are particularly attractive in:

Northern Europe

Canada

These regions have:

Strong seasonal heating and cooling demand

Existing wells with bottom casing diameters greater than 7 inches

District heating infrastructure

However, BTES requires multiple wells in a network for effective storage functionality. Single-well applications are limited.

In former oil and gas regions, these systems could help:

Balance seasonal energy demand

Stabilize district heating networks

Lower heating costs

But again , infrastructure integration is key.

6. Regulatory Complexity: A Cross-Border Challenge

Within Central Europe, regulations differ widely. Each country:

Protects well integrity differently

Has distinct liability frameworks

Applies unique permitting procedures

Liability for legacy wells remains one of the biggest non-technical barriers.

Christi stressed the need for:

Minimum integrity standards

Transferable technical criteria

A consortium-based approach

Scalable frameworks adaptable at local levels

While subsurface physics may be similar across borders, governance is not.

7. TRANSGEO’s Core Lesson: No Universal Workflow

One of the most important insights from the TRANSGEO pilot feasibility studies is this:

Reservoir characteristics are not transferable.

Engineering workflows cannot simply be copied from one site to another.

Each project requires:

Site-specific modeling

Demand-side evaluation

At least two economically viable geothermal reservoirs

At least two possible energy applications within a single well

District heating demand must already exist — or be realistically deployable.

Without demand, even technically viable wells fail economically.

8. Future Outlook: Massive Opportunity, Tough Reality

Europe has thousands of oil and gas wells.

The opportunity is immense.

But the real question is:

How many countries are willing to commit those wells to geothermal conversion?

Scaling depends on:

Policy commitment

Regulatory harmonization

District heating expansion

Financial risk-sharing models

Emerging technologies like closed-loop systems could further accelerate adoption. Christi noted that closed-loop systems are effective , but currently limited to around 100 kW, primarily for heating rather than electricity generation.

Supercritical or superhot rock concepts, requiring two to three wells, could push boundaries further , though these remain technologically and economically complex.

Final Reflection: From Abandonment to Asset

Repurposing hydrocarbon wells is not a silver bullet. It does not automatically increase productivity or extend well life.

What it does is transform stranded infrastructure into potential geothermal assets.

But viability is rare. Out of 1,000 abandoned wells, none may qualify.

The transition depends not just on geology — but on policy, economics, district heating networks, and national commitment.

The geothermal transition will not be powered by theory alone.

It will be powered by selective, strategic, economically viable conversions.

And as Christi’s insights reveal, the future of repurposed wells lies at the intersection of engineering realism and political will.

You missed: Inside the Geothermal Startup Mind: The Strategy, Funding & Sacrifices Behind Teverra’s Growth

At Alphaxioms, we continue to explore how oil and gas repurposing can unlock geothermal value , not through assumptions, but through rigorous technical assessment and economic discipline.

Alphaxioms appreciates Christi's insightful and indepth analysis on what it takes on turning Oil and gas wells into Geothermal Energy.