A milestone geothermal project in northern Germany has not succeeded in finding a good enough reservoir section in the primary target. According to information released, the reservoir turned out too thin and also came in shallower than expected at around 3,000 m (versus an expected 3,300 m). In addition, core cut from the reservoir also confirmed that the quality of the sandstone was not as good as foreseen.
Time for a Post Drill Analysis
The original target depth of the Hamburg Geothermal Project was around 3,300 m, where water of 130°C was expected to be found in Upper Triassic/Lower Jurassic Rhaetian sandstones. A seismic survey was carried out in 2010, which suggested that the reservoir interval had sufficient thickness and that no significant faulting had taken place. It is interesting to see that a 300 m mismatch between predicted and actual depth has happened; this will no doubt be part of the post drill analysis. At the same time, a 300 m difference is unlikely to be a deal breaker if the reservoir properties would have been sufficient. It is therefore more likely that quality (and thickness) form the most important barriers. The geothermal project aimed at producing 10 MW, enough to heat around 5,000 homes.
N-S seismic line showing the target horizon (Zielhorizont) for the geothermal project. The Injection well is currently being drilled. Source.
Similar issues elsewhere
It is not the first time a recent geothermal exploration well disappoints. The Leeuwarden geothermal project team in the northern part of the Netherlands is currently mulling over the question to drill a second well on their Rotliegend target after the first well proved a more challenging reservoir than expected. According to the project website, the financial outlook of the project is “very challenging”.
Part of the potential workaround proposed for the Leeuwarden geothermal project is to implement a high-temperature storage solution where water produced from the Rotliegend during summer – when there is less of a demand – is temporarily stored in a shallower aquifer. This can subsequently be produced during the winter months. An exploration well will be drilled in 2023 to further investigate the potential of the shallow subsurface to meet the requirements.
Heat pump the solution?
In Hamburg, the partnership has come up with yet another solution to make the project work, even though high-temperature storage is also being looked at. Instead of the Triassic target, the well found an Eocene sandstone that has shown better reservoir quality and a greater thickness (130 m) than expected. Obviously, the temperature is much more limited than the Triassic target (probably in the order of 40-50 degrees), but the partnership is now looking at a solution that involves heat pumps to increase the temperature to a desired 80°C.
