Deep Geothermal Drilling Preparation for Renewable District Heating

Deep Drilling Preparation for Geothermal Energy: The Erdwärme Breisgau Project

The Erdwärme Breisgau geothermal project has received approval for its next phase, allowing Badenova and Herrenknecht to begin preparing a deep-drilling site near Hartheim in Baden-Württemberg, Germany. The partners plan to invest approximately €60 million to explore a geothermal reservoir located around 3,200 metres underground and develop a heating plant for regional district heating. 

Why Deep Drilling Matters for Geothermal Heating

Deep geothermal energy can provide a stable, renewable source of heat for district-heating networks. Unlike solar and wind power, which depend on weather conditions, geothermal heating can operate continuously when the underground reservoir and surface infrastructure are technically and economically viable.

The Erdwärme Breisgau project is designed to investigate a hot-water reservoir beneath the Hartheim area. The plan involves drilling two directional wells: one production well to bring hot thermal water to the surface and one injection well to return the cooled water to the same geological formation. Badenova’s project information states that the planned production and injection wells will be approximately 3,200 metres deep and separated by about 1,350 metres. 

This arrangement is commonly known as a geothermal doublet. It enables operators to extract heat from naturally hot underground water while maintaining pressure in the reservoir through reinjection. At the surface, heat exchangers transfer thermal energy from the geothermal fluid to a separate district-heating circuit.

However, the success of a geothermal project cannot be confirmed solely through geological modelling. The actual drilling programme must demonstrate whether the reservoir contains sufficient water, whether the water can flow at commercially useful rates and whether the temperature is high enough for the intended heating network.

Regulatory Approval Enables the Next Phase

A major milestone for Erdwärme Breisgau was the approval of the project’s main operating plan, known in Germany as the *Hauptbetriebsplan*. The Landesamt für Geologie, Rohstoffe und Bergbau, or LGRB, reviewed the proposal before authorising the next stage of development. The approval permits construction of the drilling site, installation of the drilling rig and the subsequent drilling and testing activities. 

The regulatory process involved consultation with affected municipalities, specialist authorities and other public-interest bodies. Such reviews are essential because deep geothermal projects may affect traffic, groundwater protection, land use, noise levels, nature conservation and public safety.

For project developers, approval of the main operating plan is more than an administrative milestone. It confirms that the proposed drilling programme, site design and operating procedures have passed the relevant regulatory review. It also creates the legal foundation for contractors to mobilise equipment and begin construction activities.

Nevertheless, approval does not eliminate geological or commercial uncertainty. The drilling results will determine whether the reservoir can support a viable heat project. Temperature, permeability, water chemistry and flow rates must all be confirmed through drilling, well logging and testing.

Badenova and Herrenknecht Form a Joint Venture

The project is being developed through Erdwärme Breisgau, a project company jointly owned by Badenova and Herrenknecht. Each company holds a 50 percent stake, creating an equal partnership between an energy supplier and a technology and infrastructure specialist. 

The partnership combines two complementary areas of expertise:

- Badenova contributes experience in energy supply, heat production and district-heating networks.

- Herrenknecht contributes knowledge of deep-drilling systems, underground construction and large infrastructure projects.

- The project company coordinates geological development, drilling, surface construction, testing and future heat integration.

- The partners share the financial exposure associated with exploration and reservoir development.

The two companies plan to invest around €60 million in developing the geothermal reservoir and constructing the heating plant. [1] This level of investment reflects the substantial cost of drilling, site preparation, well completion, surface equipment, heat exchangers, grid connections and project management.

A joint-venture structure can help distribute financial and technical risks. It can also improve decision-making by bringing together expertise from the subsurface, engineering and energy-market sides of the project. At the same time, the partners must establish clear responsibilities for cost control, drilling decisions, safety, communication and future operations.

Preparing the Drilling Site

Preparatory work at the site near the A5 motorway and the Hardt rest area is expected to begin in autumn 2026. Planned activities include earthworks, the creation of working and storage areas, and the installation of temporary construction infrastructure. 

Before a drilling rig can be erected, the site must be engineered to support heavy equipment and intensive construction activity. A deep-drilling rig can include a tall mast, engines, pumps, mud systems, pipe-handling equipment, control systems, workshops and accommodation or welfare facilities.

Typical site-preparation activities include:

- Clearing and grading the site.

- Constructing stable foundations for the drilling rig and ancillary equipment.

- Installing drainage systems and managing surface water.

- Creating separate areas for pipes, casing, drilling fluids and excavated material.

- Establishing temporary offices, workshops and welfare facilities.

- Installing electrical, water, lighting and communications systems.

- Building access routes for heavy vehicles and emergency services.

- Creating containment systems to prevent accidental releases.

The drilling site must be designed around safety and environmental protection as well as operational efficiency. Materials need to be stored in a way that prevents contamination, while traffic routes must allow the movement of large equipment without interfering with emergency access.

The surface layout also has to accommodate the sequence of drilling operations. Casing, cement, drilling fluid additives, fuel, spare parts and testing equipment must be delivered when needed. Poor logistics can cause delays, increase standby costs and create unnecessary disruption for nearby communities.

Transport and Construction Logistics

The location near the A5 offers an important logistical advantage because large components can reach the site through a major transport corridor. For a limited period, special transports are expected to access the drilling site directly from the motorway. Traffic management measures are intended to reduce disruption to surrounding municipalities. 

Deep-drilling projects require the movement of equipment that may be unusually heavy, wide or tall. Transport planning therefore needs to address:

- Route surveys and bridge-load restrictions.

- Temporary road closures or traffic controls.

- Delivery windows for oversized components.

- Coordination with motorway and local-road authorities.

- Escort vehicles and signalling arrangements.

- Emergency access during construction.

- Communication with residents and road users.

The delivery schedule is particularly important during rig mobilisation. Equipment may arrive in a defined sequence, beginning with foundations and support systems, followed by the mast, engines, pumps, pipe-handling equipment and control units.

A well-managed logistics plan can reduce construction time and limit disturbance. It also enables the project company to provide residents with accurate information about when traffic peaks, where temporary restrictions will occur and how long the most disruptive activities are expected to last.

Designing the Wells

The well design is one of the most important technical decisions made before drilling begins. Engineers must determine the well trajectory, casing programme, cementing strategy, drilling fluids, pressure-control equipment and completion design.

The Erdwärme Breisgau project is expected to use directional wells rather than simple vertical holes. Directional drilling allows the well paths to reach a target reservoir while keeping the surface facilities concentrated on one drilling pad. It also enables the production and injection wells to be separated underground even when they originate from the same general site.

A typical deep-geothermal well may include several sections with progressively smaller diameters. Steel casing is installed and cemented in stages to stabilise the borehole and isolate geological formations. The design must account for changing pressure, temperature and rock properties with depth.

Key pre-drilling engineering questions include:

- Where is the most productive part of the reservoir?

- Which geological formations require casing and cement isolation?

- What drilling-fluid properties are appropriate for the expected rock conditions?

- How will the project respond to lost circulation or unstable formations?

- Which materials can withstand hot and chemically aggressive thermal water?

- How will production and injection performance be measured?

- What well-control systems are required for safe operation?

The design process normally integrates seismic data, geological models, existing wells, regional studies and laboratory analysis. Because underground conditions are never known with complete certainty, the drilling programme should include decision points where the well plan can be adjusted based on real-time data.

Geological and Geophysical Preparation

Before drilling, project developers analyse all available geological and geophysical information. The objective is to estimate the depth, geometry, temperature and hydraulic properties of the target formation.

Seismic surveys can help identify geological layers, faults and structural features. Existing regional data may provide information about the Upper Rhine Graben, a geologically active region with significant geothermal potential. However, seismic interpretation remains an indirect method: it can indicate promising structures but cannot fully confirm flow rates or reservoir productivity.

Additional preparation may involve:

- Reviewing regional geological maps.

- Building three-dimensional geological models.

- Interpreting seismic reflection data.

- Estimating the geothermal gradient.

- Analysing regional groundwater systems.

- Modelling expected pressure and temperature conditions.

- Assessing potential fault zones.

- Comparing the target with nearby geothermal developments.

The drilling programme then becomes an exploration and data-acquisition campaign. Measurements taken while drilling can reveal the actual lithology, fracture zones, temperatures and fluid properties. These data are used to refine the reservoir model and determine whether the project should move toward long-term operation.

Thermal Water and Surface Heat Transfer

The geothermal concept depends on transferring heat from underground thermal water to the district-heating system. The extracted water will release its heat at the surface through heat exchangers before being returned to the same geological reservoir. [1]

This closed-loop approach separates the geothermal fluid from the water circulating through homes, businesses and public buildings. It can reduce the risk of introducing geothermal minerals into the district-heating network and allows the surface system to be designed around the needs of the heat customers.

The performance of the system will depend on several variables:

- Thermal-water temperature.

- Production flow rate.

- Injection capacity.

- Heat-exchanger efficiency.

- Pumping energy consumption.

- Water chemistry and scaling tendency.

- Corrosion resistance of equipment.

- Distance to the district-heating network.

High mineral content can lead to scaling or corrosion in wells, pumps, pipes and heat exchangers. For this reason, water samples obtained during testing must be analysed carefully. The results influence material selection, maintenance planning and the design of water-treatment systems.

The thermal water also has to be reinjected in a controlled manner. Reinjection maintains reservoir pressure and supports long-term operation, but the injection well must accept the required flow without causing excessive pressure or undesirable changes in the reservoir.

Safety and Environmental Protection

Safety planning begins long before the drilling rig arrives. Deep wells involve high pressures, heavy machinery, rotating equipment, high temperatures and complex fluid systems. A comprehensive health, safety and environment programme is therefore essential.

Important safety measures include:

- Well-control procedures and emergency response plans.

- Pressure-control equipment and blowout-prevention systems.

- Clearly marked exclusion zones.

- Training for drilling and construction personnel.

- Fire protection and medical response arrangements.

- Safe handling of chemicals and drilling fluids.

- Continuous monitoring of critical drilling parameters.

- Regular inspections and equipment maintenance.

Environmental protection focuses on groundwater, soil, surface water, noise, air quality, traffic and waste management. The site should be constructed with suitable containment and drainage systems so that drilling fluids, fuels and other materials cannot enter the surrounding environment.

Noise and lighting can become significant issues during continuous drilling operations. The project company must therefore apply appropriate mitigation measures and communicate clearly about the timing and duration of noisy activities.

Induced seismicity is another consideration in geothermal development. Monitoring systems can detect small seismic events and support operational decision-making. The project’s communication strategy should explain both the benefits and the potential risks without minimising legitimate public concerns.

Testing the Geothermal Reservoir

Drilling alone does not establish whether a geothermal project is commercially viable. After reaching the target formation, the wells must undergo testing to assess the reservoir’s performance.

Testing may include:

- Temperature measurements.

- Pressure monitoring.

- Flow testing.

- Injection testing.

- Well logging.

- Water sampling.

- Transient pressure analysis.

- Interference testing between wells.

These tests help determine the sustainable production rate and the amount of useful heat that can be delivered. They also provide information about pressure communication between the production and injection wells.

The project source material emphasises that the drilling phase will determine the actual temperatures and flow rates available from the reservoir. Only after these characteristics are confirmed can the partners decide whether the geological conditions support an economically viable operation and possible future expansion. 

This staged approach is important because geothermal projects carry resource risk. A reservoir may have an attractive temperature but insufficient permeability, or it may produce water at a useful flow rate but with chemistry that creates high operating costs.

Community Engagement and Public Information

Public communication is a central part of preparing a deep-drilling project. Residents may have questions about traffic, noise, construction duration, groundwater, seismicity, land use and the eventual benefits of the project.

The project company plans to offer site tours during the drilling phase so that interested members of the public can learn about the work directly. Such activities can make a highly technical project more understandable and provide opportunities for dialogue.

Effective engagement should include:

- Early notification of construction activities.

- Clear explanations of the drilling schedule.

- Information about transport routes and temporary restrictions.

- Publicly accessible environmental and safety information.

- A named contact for questions and complaints.

- Regular progress updates.

- Explanations of testing results and next decisions.

The benefits should also be described in concrete terms. A successful project could provide a local renewable heat source, reduce dependence on fossil fuels and support the expansion of district heating in the Freiburg region. Some reports state that the wider project ambition includes supplying thousands of households with geothermal heat. 

 Project Timeline and Decision Points

The current schedule separates site preparation from the main drilling campaign. Preparatory construction is expected to begin in autumn 2026, while the actual drilling is planned for the second half of 2027.

A typical project sequence may include:

1. Completion of detailed engineering and procurement.

2. Preparation of the drilling pad.

3. Installation of access, drainage and utility infrastructure.

4. Mobilisation of the drilling rig and support equipment.

5. Drilling of the first well.

6. Logging, completion and testing.

7. Drilling and testing of the second well.

8. Reservoir evaluation and economic assessment.

9. Construction or finalisation of the heating plant.

10. Connection to the district-heating network.

Each stage should have measurable completion criteria. For example, the project team may decide in advance which flow rate, temperature range and pressure behaviour would justify proceeding to the next phase.

Why the Project Is Significant

Erdwärme Breisgau illustrates the growing interest in deep geothermal energy as part of Germany’s heat transition. The project links subsurface resource development with district-heating infrastructure, creating a pathway for replacing part of the fossil-fuel supply used for urban and regional heating.

Its location in the Upper Rhine area is significant because the region has long been considered promising for geothermal development. At the same time, the project demonstrates that resource potential must be verified through careful drilling and testing rather than assumed from regional geology alone.

The cooperation between Badenova and Herrenknecht is also notable. It brings together the operational requirements of a heat supplier with the engineering capabilities of a specialist in underground infrastructure. Their shared investment of approximately €60 million signals confidence in the potential of geothermal heat while acknowledging the substantial cost of moving from exploration to operation. 

Conclusion

Preparing a deep-geothermal drilling project involves far more than transporting a rig to a construction site. It requires regulatory approval, geological analysis, well engineering, logistics, environmental safeguards, safety planning, reservoir testing and continuous communication with local communities.

For Erdwärme Breisgau, approval of the main operating plan allows Badenova and Herrenknecht to proceed with site preparation near Hartheim. The next decisive milestone will be the drilling campaign planned for the second half of 2027, when the project team will determine whether the approximately 3,200-metre-deep reservoir can deliver the temperature and flow rates required for reliable district heating. 

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