The greenhouses in The Netherlands are a major user of natural gas. The Trias Westland project is exploring the possibility to use geothermal heat as an alternative source for heating these greenhouses.

How does the harvesting of geothermal heat work?

Earth’s temperature rises with depth from the surface to the core. This gradual change in temperature is known as the geothermal gradient. In most parts of the world, the geothermal gradient is about 25° C per 1 kilometre of depth (1° F per 77 feet of depth).

Almost anywhere in the world, geothermal heat can be accessed and used immediately as a source of heat. The heat (energy) is stored in water which is present in the rock pores. When a well is drilled to this reservoir you can produce the brine. In some cases the water comes out of the ground automatically and in others you need a pump. In the Netherlands submersible pumps are required. After producing the warm water, the heat can be transferred to a heat network by heat exchangers.

Low-temperature geothermal energy can be used for heating greenhouses, homes, fisheries, and industrial processes. Low-temperature energy is most efficient when used for heating, although it can sometimes be used to generate electricity. High temperature flows can be used for electricity generation.

In the Westland area, how many MegaJoules of energy is currently used for heating greenhouses?

Currently, the Westland area uses 39 petajoules (PJ) per year of energy of which Greenhouses account for 31 PJ/year.

What are the main sources of this energy?

Total energy usage 31 petajoules per year. Of which 27 PJ comes from gas and 4 PJ from electricity.

How much of this can potentially be replaced with geothermal

The potential for sustainable use of geothermal energy is 38 PJ/jr.

Which layer do you want to research with the test boreholes?

The layer being researched here is referred to as the Trias layer. It was deposited between 252,2 till 201,3 million years ago. The name Trias refers to it being a three layered sequence; Buntsanstein, Muschelchalk and Keuper. In the Netherlands the Buntsantstein is the best reservoir for geothermal which consists of three sub-formations, the Hardegsen, Detfurth and Volpriehausen.

What are the characteristics that make a layer suitable for geothermal energy?

Good porosity and permeability as well as good layer thickness.

Before the drilling of the test borehole started, have you performed other tests of the geology and what were the results?

A lot of information about the Trias in the area is known from oil and gas drilling. Also seismic data is available.

Have there been similar drills in the area already?

Not till this depth. The deepest wells in the area are around 3500m. However, in the Netherlands there are multiple wells deeper than 5000 meter, so drilling technology is sufficient.

Once the borehole reaches a layer, how do you test the geothermal potential?

We hang in a submersible pump and produce the water to surface.

What is the timeline for the project?

Well tests will be performed in January for the first well. In case this is a success, we will drill another well. If not, we will open the well in a shallower layer.

Can the test borehole eventually be used for the production of geothermal energy?

Yes, if the Triaslayer is viable then a second borehole will be made. One from water production and the other for injection.

How long does a borehole stay productive?

The reservoir models predict a lifetime of at least 30 years, but probably more in the range of 50-70 years before the production well produces cold water. Another problem can be the wellbore integrity. Trias Westland has many corrosion and scaling mitigations in place, but there is always a risk that the well encounters problems during production.

How many MegaJoule does a borehole have to produce per year to be economically feasible at current energy prices?

The production capacity of Trias Westland will be approximately 25-45 MWth. Which saves about 25-40 million m3 of gas.

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