Breakthroughs in geothermal drilling: Eavor’s FOAK closed-loop commercial project in Germany

MARK HODDER, Eavor Technologies 

As the energy industry seeks to align growing energy demand and the need for clean technologies, geothermal energy is gaining renewed attention, not just for its sustainability, but for its potential to deliver reliable baseload heat and power. Eavor Technologies, a Canadian innovator in Advanced Geothermal Systems (AGS), is on a mission to enable geothermal anywhere in the world, regardless of the local geology, with its closed-loop solution, the Eavor-Loop^TM.  

Eavor has taken a bold step forward in proving the scalability of this technology, with its Geretsried project in Germany. As the first commercial implementation of the company’s closed-loop geothermal system, the project is setting new benchmarks in drilling performance.  

For those familiar with oil and gas operations, the technical parallels in drilling methodology, equipment adaptation, and performance optimization will be immediately recognizable. What sets this project apart is how those familiar techniques are being reimagined for geothermal applications, drilling deeper and reaching hotter temperatures, with increasingly impressive results.  

These results—proof of the ability to optimize drilling performance and come dramatically down the learning curve at a first of a kind project—provide tangible real-world results that indicate future Eavor-Loops can be scaled globally and affordably. 

PROJECT OVERVIEW 

Fig. 1. Conceptual visualization of how an Eavor-LoopTM works.

The Geretsried project features four Eavor-Loops drilled from a single surface pad, targeting the Jurassic Malm carbonate reservoir in southern Germany. The Malm formation is a tight, fractured carbonate with low porosity (~3%), low permeability (~0.1–10 mD), and high unconfined compressive strength (~80-180 MPa). These characteristics make it unsuitable for conventional hydrothermal or EGS systems but ideal for closed-loop geothermal.  

The local geothermal gradient (~34°C/km) supports high thermal output at a 4,500-m depth, and the formation’s mechanical competence enables long horizontal multi-laterals (>3,000 m) to achieve greater than 8,000-m well lengths for each drilled lateral. The project design is coupled with surface facilities and an Organic Rankine Cycle (ORC) power plant. Unlike conventional hydrothermal systems, Eavor’s technology does not require underground aquifers of hot water, nor does it use fracing, which makes the closed-loop geothermal system ideal for this area in Germany.  

An Eavor-Loop consists of two sets of multi-lateral wellbores, positioned within 60 to 80 m vertically in a competent formation, as depicted in the conceptual schematic, Fig. 1. The main wellbores are drilled from a common surface location, and the laterals are connected toe-to-toe underground, essentially forming a massive subsurface radiator.  

After connection of the laterals, heat is collected from the subsurface through conductive heat transfer into a controlled working fluid, sealed off from the surrounding rock. The multilateral wells are not cased with steel but rather are sealed off with Eavor’s proprietary Rock-Pipe^TM sealant (see more under enabling technologies). The nature of the closed loop, with a colder inlet fluid temperature than on the outlet side, coupled with minimal open hole frictional effects, allows for a natural thermosiphon that circulates the working fluid through the surface facility without the need for any parasitic pump loads. 

DRILLING PERFORMANCE AND LEARNING CURVE 

Fig. 2. Geretsried Loop 1 average lateral bit run lengths for each lateral on both wells, overlaid with on-bottom ROPs. A and B represent the outlet and inlet wells, respectively.

The first Eavor-Loop at Geretsried involved drilling and connecting six lateral pairs; 12 approximately 3,000-m horizontal wells, the longest of which reached 3,267 m and total measured depth of 8,145 m. Once the first laterals were drilled and connected, the drilling program was refined and optimized by identifying stratigraphic targets, refining fault models, and interpreting real-time drilling data to guide trajectory adjustments and mud system changes.  

This repetition enabled a steep drilling learning curve, with each run refining bottomhole assemblies (BHAs), bit selection, and drilling parameters. The result: a more than 90% improvement in on-bottom rate of penetration (ROP) and a significant reduction in non-productive time (NPT). 

Key performance indicators included: 

• On-bottom ROP: From less than 15 m/hr on the first lateral, to over 25 m/hr on the sixth. 

• Bit run lengths: Improved from an average of 1,200 m to over 3,000 meters, with several laterals drilled to total depth (TD), using a single bit, Fig. 2. 

• Overall drilling time: Reduced from over 100 days, each, for the first four lateral pairs to approximately 50 days for the final two. 

These gains were achieved despite non-technology-related challenges, such as borehole instability and hydraulic communication between laterals, which were mitigated through operational adjustments and fluid design changes. 

ENABLING TECHNOLOGIES 

Several proprietary and adapted technologies played a critical role in enhancing drilling performance: 

• Insulated drill pipe (IDP): Modified to reduce thermal conductivity from 23 BTU/h•ft•°F to less than 0.75 BTU/h•ft•°F, representing a >95% reduction. This enabled drilling in rock temperatures exceeding 150°C while maintaining BHA temperatures below 120°C, allowing the use of conventional 150°C-rated oil and gas tools. 

• Rock-Pipe^TM sealant: Eavor's proprietary sealing method reduced permeability by more than 10x. The two-stage chemical process sealed near-wellbore permeability, maintaining a closed system while cutting well construction costs by over 40%, compared to cemented casing. 

• Active magnetic ranging (AMR): Initially deployed via wireline, AMR was later integrated into the BHA, enabling real-time ranging and reducing ranging time by over 80%. This allowed for precise wellbore intersections at over 8,000 m on each lateral pair on the first attempt. 

• Multilateral sidetracking: Sidetracking operations were optimized using bent-housing motor assemblies and improved whipstock and milling configurations. A one-trip sidetracking system under development is expected to reduce sidetrack initiation time to under four days, saving up to a day per operation. 

INSULATED DRILL PIPE (IDP) EXPLAINED 

Eavor’s IDP technology enables lower drilling fluid temperatures which, when combined with mud cooling technology, allows for a step change in the ability to cool bottomhole assemblies efficiently at depth. Heat flow into the pipe is minimized by an internal and/or external coating, reducing counter-current heat transfer and the exposure of the drilling fluid to high temperatures. Subsequently, cooler mud is delivered to the bottomhole assembly (BHA) allowing better reliability and less tool failures. Additionally, the introduction of cold drilling fluid at the bit-rock interface reduces the tensile strength of the rock and can increase the effective rate of penetration.  

The drill pipe insulation system can be applied to any size and grade of existing industry drill pipe to suit the operator’s requirements. The pipe can be handled with conventional tools and equipment, requiring no modification to existing drilling rig technology. 

ROCK-PIPE™ EXPLAINED 

Rock-Pipe™ is Eavor’s completion method for sealing the open-hole sections of an Eavor-Loop, making sure the working fluid stays isolated from the surrounding rock. This method eliminates the need to cement casing/liners in the multi-laterals. This allows for greater surface area for heat transfer and significantly reduces the complexities associated with multiple liners being set in one motherbore. 

Rock-Pipe works by pumping a fluid train into one or more legs of an Eavor-Loop after the laterals have been intersected using Eavor-Link™ AMR. The fluids create a chemical reaction within the rock matrix, which reduces the near-wellbore permeability of the open-hole section. In field tests at Eavor-Lite™ in Canada, the permeability reduction from Rock-Pipe showed over 99% reduction in leak-off rates over the five-year life of the pilot.  

Fig. 3. Duration of ranging and intersection activities across each lateral, differentiating between conventional ranging techniques and the Eavor-LinkTM AMR system. Prior to Lateral 4 Eavor-LinkTM was run in validation mode, switching to primary after operational issues with the wireline tools on that lateral.

The result is better thermal performance, since there’s no fluid exchange with the formation and reduced water usage, due to the low leak-off rate. Rock-Pipe is intended to be effective for the entire life of an Eavor-Loop. It is possible, however, to re-apply Rock-Pipe to an Eavor-Loop in the future if required. 

ACTIVE MAGNETIC RANGING (AMR) EXPLAINED 

The construction of each subsurface loop requires the successful intersection of each lateral, which in turn requires the ability to detect and steer from one wellbore into the other. Successful execution on the first lateral pairs in Geretsried used existing off-the-shelf ranging tools and techniques, using pump-down wireline sondes at each ranging point in the well. Several ranging shots are required along the lateral length; therefore, significant time is attributed to wireline operations.   

In conjunction with several industry partners, Eavor developed a novel solution that incorporates the same active magnetic ranging (AMR) components into a fixed BHA component. The tool collects and analyzes the data downhole, allowing for “on the fly” ranging shots during drilling, removing the need to trip wireline into and out of the hole.  

This represents a step-change in lateral performance and is further improved with each ranging operation through a similar learning curve methodology, as noted earlier. This technology was implemented in Geretsried from the fourth lateral onward, after experiencing operational failures with the wireline-based tools, and has a noticeable impact on drilling times and subsequently on project economics, reducing the time dedicated to ranging activities by more than 80%, Fig. 3. 

OPERATIONAL CHALLENGES AND MITIGATIONS 

Two major challenges impacted early drilling operations: 

Fig. 4. Average durations from the first four vs final lateral pairs, demonstrating the improvement from mitigating and resolving the key drilling challenges. Planned design changes to eliminate hydraulic communication on future loops, combined with overall learning curve, provide line of sight to delivery of less than 20 days per lateral pair.

• Hydraulic communication: Poor cement coverage through the casing exit intervals led to unintended fluid flow between lateral pairs, forcing sequential rather than concurrent drilling. Isolation packers and improved cementing strategies are planned for future loops to restore concurrent drilling capability. 

• Borehole instability: Unexpected geomechanical instability of the Malm formation caused stuck pipe events. High-resolution acoustic image logs revealed breakout patterns and weak bedding planes, guiding mud weight and trajectory adjustments, eliminating stability issues in the final two lateral pairs. 

Despite these setbacks, the final two lateral pairs showed marked improvement, averaging 50 days each—down from over 100 days each for the first four. With proper isolation, future lateral pairs are expected to be completed in under 20 days, Fig. 4. 

These initial challenges in early drilling operations at Geretsried are indicative of the learning curve that begins with a new first-of-a-kind project. The project is a proving ground for Eavor’s closed-loop technology and a real-world demonstration of coming down the learning curve to enable global expansion, affordability, and scalability. 

SCALABILITY AND FUTURE IMPACT 

Fig. 5. A bird’s eye view of Eavor’s facility at Geretsried, Germany.

The Geretsried project not only validates the Eavor-Loop concept but also sets the stage for broader deployment. By pushing lateral lengths and depths beyond initial plans, Eavor has demonstrated the potential to boost energy output by more than 35% per loop. Seismic reprocessing, stratigraphic modeling, geomechanical simulations, and real-time geological supervision have created a robust subsurface framework that supports future scalability. In addition, further torque and drag optimization supports extending lateral drilling lengths and increased lateral count per parent bore, and IDP effectiveness enables loop placement in deeper and hotter targets.   

These learnings are directly transferable to future European projects and beyond, offering a pathway to competitive levelized cost of heat (LCOH). The combination of improved drilling efficiency, enabling technologies, and design optimizations positions Eavor to deliver scalable geothermal energy with oil and gas-style execution. 

Looking ahead, other areas to further lower the cost of supply include leveraging economies of scale by honing the supply chain, creating fit-for-purpose Eavor-Loop rig designs and maximizing Organic Rankine Cycle efficiencies. 

CONCLUSION 

Eavor's Geretsried project (Fig. 5) exemplifies how technical innovation and operational discipline can redefine geothermal drilling. For oil and gas professionals, the parallels in drilling methodology and the adaptation of conventional tools to geothermal contexts offer a compelling case for cross-sector collaboration. The knowledge and expertise in oil field services are crucial to scaling geothermal closed-loop technology globally. As Eavor continues to refine its approach, the promise of scalable, cost-effective geothermal energy everywhere becomes increasingly tangible. 

REFERENCE 

Hodder, M. et al “Multi-Lateral Drilling Learning Curve at Eavor’s Geretsried Project.” GRC Transactions, Vol. 49, 2025, Reno, NV, USA (2025) 

MARK HODDER is Eavor Technologies’ lead for well engineering. He is an expert in well design, modelling, and efficient execution of drilling operations, with global expertise encompassing a variety of well types and basins that include thermal SAGD / CSS, carbon capture and storage (CSS), and geothermal. Prior to joining Eavor, Mr. Hodder worked for Royal Dutch Shell as senior well engineer and subject matter expert, providing technical guidance to challenging and complex well designs in Shell’s global onshore portfolio. .