The first well of the Aardwarmte Alton geothermal project in the Dutch municipality of Dijk en Waard reached its reservoir at 2.5 km without trouble. Then it was tested, and it delivers less water than expected. HVC, the developer, has put the project on hold to decide whether drilling the remaining wells is technically and economically justified, ThinkGeoEnergy reported on 10 November; HVC's own notice is dated 29 October.
Drilling had started in September. The rig is to be dismantled and the well sealed while the company studies its options, a restart among them. HVC's director of heat called the result unexpected: about 20 km away, eight geothermal wells tap the same geological layer and are in successful use.
The plan on paper
ThinkGeoEnergy gives the outline of what was intended:
- four wells, each to about 2,400 m, aiming at water of 85 °C
- approximately €75 million approved by the shareholders for drilling and construction
- heat for homes and other buildings on HVC's existing heat network in the area
That network is not short of heat today. According to HVC it is fed by the company's biomass plant and its waste-to-energy plant in Alkmaar, and existing customers are not affected. What the pause does to the planned expansion of the network is still being looked at. HVC currently operates 18 geothermal wells supplying approximately 15 MWth, ThinkGeoEnergy writes.
Less water means less heat, whatever the temperature
A well test looks at three things: water temperature, production rate and how the water moves through the reservoir. HVC's statement points at the second. That matters for everything above ground, because the thermal output of a doublet is flow times temperature drop, and only one of those can be influenced at the surface.
If wells give less water, the operator's lever is to cool that water further before it goes back down: lower return temperatures from the network, a heat pump behind the geothermal exchanger, or both. Each degree taken out of the brine is paid for with heat transfer surface or compressor power. It is one reason geothermal operators care so much about return temperatures from their customers' substations - a badly balanced building that sends back warm water costs the well field output.
The other lesson is about sequence. Kutno in Poland, which received funding last week, has published an expected flow of at least 150 m³/h, but there too only the wells will tell. Surface plant - exchangers, pumps, filters - is best fixed after the test, when flow and water chemistry are known. A plate heat exchanger can be re-plated for a different duty; a borehole cannot.
Sources: ThinkGeoEnergy, HVC
