Frequently Asked Questions
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Frequently Asked Questions (FAQs)
13 - How is the seismic risk (if any) addressed?
Seismicity is a serious consideration in any technology that interacts with the deep subsurface. However, the seismic risk of Endoria's closed-loop Ultra-Deep Geothermal concept is fundamentally different from the mechanism that caused the earthquakes associated with oil and gas production (extracting materials from the subsurface of the Earth).
In Groningen (the northern province of The Netherlands), natural gas was extracted from a reservoir at approximately 3 km depth. Decades of gas production reduced reservoir pressure and caused compaction of the reservoir rock. This changed the stress conditions along existing geological faults and resulted in induced earthquakes. The relatively shallow depth of approximately 3 km, combined with the soft soils in the region, also contributes to the strong effects experienced at the surface.
Endoria's concept is fundamentally different. The system is designed as a closed-loop geothermal system: the working fluid circulates within an engineered subsurface system and is not permanently extracted from the surrounding geothermal formation. There is therefore no comparable depletion of a gas reservoir and no requirement to produce hydrocarbons or continuously remove formation fluids from the subsurface.
Furthermore, Endoria's target is the SuperHot temperature regime, with the required depth determined by the local geothermal gradient rather than by a fixed drilling depth. In continental Europe this may require drilling considerably deeper than the Groningen gas reservoirs.
That said, greater depth and a closed-loop configuration do not mean that seismicity can be ruled out entirely. Drilling, changes in pressure and temperature, thermal stresses and the presence of pre-existing geological faults can potentially influence the stress state of the subsurface. This is why geological and geomechanical characterization, continuous monitoring and site-specific seismic risk assessment are essential parts of Endoria's development approach.
Importantly, Endoria's concept does not depend on hydraulic stimulation of a large fracture network in the same way as conventional fracture-based EGS projects. This is expected to substantially reduce the principal mechanism associated with induced seismicity in such systems. Nevertheless, the actual seismic response must be demonstrated and validated on a project-specific basis.
In short: Endoria does not claim that seismicity is impossible. Rather, the closed-loop design is intended to fundamentally reduce the mechanisms that can lead to induced seismicity, while the greater operating depth provides an additional physical difference from the shallow Groningen gas reservoirs.
SodM ('Staatstoezicht op de Mijnen' - the Dutch State Supervision of Mines) itself recognizes that geothermal energy can induce seismicity and therefore advises particular caution in areas with existing seismicity or active faults. That makes site selection and geomechanical assessment particularly important for any Dutch project.
Visualized:
Groningen: gas extraction → reservoir pressure depletion → reservoir compaction → stress changes on existing faults → induced earthquakes.
Endoria: closed-loop circulation → no permanent extraction of geothermal fluids → no comparable reservoir depletion → fundamentally different subsurface pressure regime.
Mechanical vibrations and noise
The challenge of Ultra-Deep Geothermal is not simply drilling deeper. It is maintaining control of the entire drilling and well system as depth, temperature, pressure and mechanical loads increase simultaneously.
During drilling, the drill bit and bottom-hole assembly generate mechanical vibrations as the bit interacts with the formation. These include axial, torsional and lateral vibrations. Such drilling dynamics are fundamentally different from induced seismicity caused by geological fault movement.
As drilling progresses into deeper and harder formations, managing these dynamics becomes increasingly challenging because of the increasing length of the drillstring, higher temperatures and pressures, and more demanding rock conditions. Advanced BHA design, drilling-parameter optimization, downhole monitoring and vibration management are therefore essential.
Drilling a deep geothermal well inevitably generates mechanical vibrations within the drilling system. However, these vibrations are fundamentally different from induced seismicity and are expected to have a predominantly local range. This does not mean that seismicity risk is eliminated. Site-specific geomechanical assessment, monitoring and operational controls remain essential.
The main sources of vibration at the surface are the drilling rig, drive system, pumps, generators and associated equipment. The drill bit itself operates deep below ground, and vibration energy generated at the bit is progressively attenuated as it propagates through the surrounding rock.
As wells become deeper, managing drillstring dynamics becomes increasingly challenging because of the extreme length of the drillstring, higher temperatures, pressures and demanding rock conditions. This is primarily a drilling-engineering challenge rather than an indication that significant vibration will be transmitted to the surrounding area.
For a Dutch project, potential vibration and noise impacts on nearby residents (radius: approximately 300 m.) and sensitive buildings would be assessed during the permitting and engineering process. Site-specific modelling, baseline measurements, vibration monitoring and appropriate mitigation measures can be used to ensure that the drilling operation remains within applicable environmental requirements.
In practice, noise from the surface drilling installation is expected to be a more relevant potential source of local disturbance than ground vibration from the deep drilling process itself.
Technical Disclaimer & Risk Assessment
The technical risk assessment presented herein has been compiled to the best of our knowledge and belief, based on available scientific and industry knowledge, internal expertise, and consultations with specialized geothermal and drilling professionals. It is intended to provide an overview of the principal geological, technical, operational, environmental and regulatory risks currently identified in connection with Ultra-Deep Geothermal Energy and Enhanced Geothermal Systems (EGS).
However, Ultra-Deep Geothermal and particularly SuperHot EGS remain emerging technologies, and significant aspects of deep subsurface conditions and high-temperature operation have not yet been demonstrated at commercial scale. Consequently, there may be additional technical, geological, operational or other risks that are currently unknown, insufficiently understood, or not yet identifiable at the present stage of technological development.
The risks identified in this assessment should therefore not be regarded as exhaustive. Actual subsurface conditions, drilling performance, well behaviour, temperature, pressure, material performance, heat-transfer characteristics and other project-specific conditions may differ materially from current assumptions and models.
Further geological investigation, engineering studies, exploratory drilling, testing, monitoring and regulatory assessment will be required to progressively validate assumptions and reduce uncertainty as each project advances. This assessment is therefore intended as a high-level technical overview and should not be regarded as a definitive assessment of all risks associated with a specific project or as a substitute for detailed project-specific engineering, safety and regulatory assessments.