Denmark has one of the most widespread uses of district heating covering more than two-thirds of all households and it is still being expanded.

As part of the decarbonization efforts of the district heating network the Danish Energy Technology Development and Demonstration Programme has awarded more than 11 million Euro for a new closed geothermal well concept to be tested in a new well to be drilled in Aalborg, Northern Denmark and it is expected that the well will be ready to produce geothermal heat late 2026 for direct use without heat pumps with the local utility company as the heat off taker.

The new concept is a co-axial closed loop well solution drilled to 3-5 km with a horizontal section of 3-5 km with an outer casing/liner and a vacuumized pipe-in-pipe completion inside. A circulating fluid will flow in the outer casing string of the co-axial solution, and in this process, the fluid will be heated along the horizontal section to the approximate temperature of the subsurface before returning to the surface in the inner insolated pipe with a continuous vacuum, that nearly eliminates the heat loss, as it acts like a long thermo flask.

To project will consist of a number of phases and tasks to ensure a successful project execution, learning process and dissemination of the results.

This project is the steppingstone for multi well geothermal projects (5-10 wells) drilled in start pattern to directly supply cities with geothermal heat to the district heating network through a heat exchanger.

Determining the economic feasibility of deep geothermal projects requires precise numerical forecasting of thermal performance. By simulating the injection of supercritical CO₂ near its critical point using different thermodynamic models, this study assesses the potential of CO₂ closed-loop geothermal systems. To evaluate the precision and reliability of existing tools, we compare results from a commercial reservoir simulator and a custom-developed numerical model.

Distinct equations of state (EOS), such as Peng–Robinson (PR), Span–Wagner (SW), and Soave-Redlich-Kwong (SRK), are employed for predicting PVT properties. Consistent EOS usage across simulation platforms enables accurate comparisons and highlights modeling sensitivities near critical conditions.

Simulation results demonstrate the advantages of using supercritical CO₂ as a working fluid. Its lower viscosity and higher thermal expansivity compared to water contribute to enhanced heat extraction and a strong thermosiphon effect. Temperature-induced density variations further drive natural convection, enhancing fluid circulation in closed-loop systems and maximizing energy recovery without additional pumping.

Variations in PVT property predictions between EOS implementations underscore the importance of careful input selection and improved simulation accuracy, particularly under near-critical conditions. Our numerical model offers insights into thermosiphon dynamics and wellbore heat transport, while the commercial simulator excels in evaluating reservoir-scale thermal performance.

Our analysis confirms the viability of CO₂-based closed-loop geothermal systems for efficient and sustainable heat generation. The findings underscore the importance of enhancing simulation tools—such as expanding EOS libraries and refining near-critical fluid modeling—and offer a pathway for bridging the gap between conventional petroleum engineering tools and renewable energy solutions.

In 2023, a major energy provider and operator of an extensive district heating network announced the development of a deep geothermal power plant. By the end of 2024, drilling operations commenced, and by May 2025, the third and final well successfully reached its planned total depth, targeting a naturally occurring hot water reservoir approximately 3,000 meters below the surface.

As of now, production testing—intended to assess formation water temperature, chemical composition, and flow rates—has not been conducted. Therefore, this paper focuses on the planning and execution phases of the drilling campaign.

We present Weatherford’s Lost-in-Hole (LIH) Preventive Initiative as a continuous improvement strategy, highlighting lessons learned from the first to the third well. Emphasis is placed on the joint efforts of Weatherford’s Drilling Engineering and Interpretation and Evaluation teams in accurately interpreting downhole and surface data to assess risks and inform our client on mitigation strategies and drilling practices. The Initiative serves as a replicable example, crucial for minimizing wellbore stability issues, preventing lost-in-hole incidents and tool damage, reducing Non-Productive Time (NPT), and ultimately enhancing drilling performance across the project.

Over the past few years, Kemco has successfully engineered, planned, and executed several complex heavy workover (WO) operations on geothermal wells in Bavaria and Rhineland-Palatinate, Germany. Contrary to common misconceptions, workovers are not straightforward, quick projects; they involve numerous interdependent processes and demand meticulous planning and engineering due to their inherently dynamic nature.

Each region in Germany presents unique well failure mechanisms, necessitating a thorough analysis of root causes to implement effective, long-term remedial actions.

This presentation shares insights from Kemco's experience, highlighting best practices during engineering, planning, and execution phases, as well as common failure causes and mitigation strategies.

In SGP-TR-223&224 we derived a double-convolution integral, involving solely the measured signal of a conservative tracer, to predict the ‘fluid mining’ output of a co-produced micro-solute during fluid re-circulation in a geothermal reservoir operated by means of a well doublet, and illustrated our formula’s use for various reservoir settings in the Upper Rhine rift valley and the N-German sedimentary basin.

It was perceived as a major advantage that the tracer-based approach works as a model-independent tool, viz. the signal of any conservative artificial tracer, as recorded in inter-well or inter-horizon circulation tests (that are conducted under flow conditions representative of the future ‘fluid mining’ process), can be used to predict the geothermal co-production output of any fluid-‘mined’ solute (in particular: lithium), and its gradual depletion during reservoir fluid turnover, irrespective of the availability, parametrizing, and calibration of a reservoir model (distributed- or lumped-parameter, numerical or analytical, assuming whatever structure and boundaries).

In SGP-TR-227 we used the incipient signal of a conservative tracer recorded for a hydrothermal reservoir (Upper Rhine rift valley, Eastern side) to constrain the prediction of lithium depletion and cumulative lithium output during the first decade of the intended ‘geothermal co-production’ operation.

After one more year of tracer signal recording, the further tracer data available can also be exploited for model calibration — the more so, as a reliable reservoir model still remains indispensable for thermal output forecast. Though generally unsuited for hydraulic parameter calibration, mid-to-late tracer signals may (significantly) constrain the uncertainty associated with remote reservoir boundaries.