Although the 4km-deep hole drilled by Trias Westland provided a ‘wealth of data’, the extraction of sustainable heat from the Trias layer is not sufficiently profitable. The organisation has therefore decided to fall back on Plan B and extract warm water from the Lower Chalk layer. This option is anticipated to deliver 19 to 22 MW, which is not enough to supply all the growers that have committed themselves to this project with geothermal heat.

A core of 30 metres of stone was brought up in the last specimen extracted from the drill hole. A study of this core revealed that the porosity (permeability) of the rock from the Trias layer was zero. This means that the flow of water at this depth is very difficult, if not impossible. Additionally, traces of gas were discovered in the pores of the sandstone, rendering the performance of a normal well test using a pump impossible. “An enormous disappointment,” says Floris Veeger, project manager for geothermal heat of Trias Westland. This prompted a decision to close off this deep section with two concrete plugs and to extract heat from the shallower Delft sandstone layer, in line with the other projects in the Westland area. This was disappointing for the participants and initiators, because no new layer of soil was made accessible that would help phase out the dependency on natural gas in the province of Zuid-Holland.

Well test

The Delft Sandstone Layer is nevertheless thicker and more permeable than anticipated. Apart from this, an additional layer of sand (at a greater depth) was discovered, which will not be used for this project, however. The organisation expects to extract water of a temperature of 85 to 90 degrees from the Delft Sandstone layer, at a depth of 2.3 km. The first well test is expected to take place next weekend. If, after this, the definitive decision is made to drill the second well, a second well test will take place at the end of April which will provide more information about the exact heat yield of the geothermal project. To be able to provide all participants with sufficient geothermal heat, a second doublet will be necessary. Director Marco van Soerland does not exclude that Trias Westland will do this, even though no concrete plans have been drawn up for this purpose. The potential yield in geothermal heat from the Lower Chalk layer in the Westland area is estimated at 300 to 400 MW.

Text/photos: Mario Bentvelsen.