The EPOS-eNLarge project includes plans to drill a 4.5 km deep well for scientific monitoring. We’ve asked TU Delft Prof. Phil Vardon and project manager Dr. Susanne Laumann about this.
Q: How special is a 4.5 km deep well?
A: It’s pretty unusual to do this and even more unusual to do so for science. There are more than 4000 boreholes deeper than 1km in the Netherlands, yet only 50 deeper than 4.5km and only 9 of these are onshore. Of these, these were mainly drilled to explore for oil and gas and therefore have limited data available, and there is only one borehole which is not abandoned. The last of these boreholes was drilled around 20 years ago. This is the first time a monitoring well as deep as this has been drilled in a geothermal system.Q: Why so deep? Why do we care what happens at 4.5 km?
A: Two reasons. First, we want to monitor the fluid flow from the geothermal wells on campus. In the geothermal system hot water is extracted from the so-called producer well and cold water re-injected in the injector. Both of these wells are located at a depth of around 2.5 km. The rocks in which the geothermal project is installed have varying flow-through properties. The hot and cold fluids will therefore move heterogeneously through these rocks, and we want to understand how it does so. We have to drill deeper than the 2.5 km of the well, in order to be able to monitor this process in three dimensions.
Secondly, we want to investigate the geothermal potential of deeper geological formations with high temperatures >120 °C, that are suitable for electricity production. In the Netherlands, shallower formations are usually exploited, where the cooler temperatures are much less suitable for generating electricity. The deep formations are likely to be fractured and have lower permeability, such that the flow behaviour may be more complicated. This calls for research.
Q: What can you do with this well?
A: We will use it for seismic and electromagnetic monitoring of an operating geothermal system, as well as for in-depth research on various geological formations (by taking cores and performing geophysical logging). We consider this to be a multipurpose borehole. While we have detailed plans, we also think the opportunity of drilling to such depths should be exploited beyond the geothermal aspects. We know that the samples and data will be in high demand, so we will organise a workshop before detailed designing and drilling to ensure we make maximum use of the opportunity to undertake such a special project. We will get additional input from an international and multi-disciplinary group of people from science, geothermal industry, governmental institutions and geological surveys.Q: When will this well be drilled?
A: Within the next 5 years. Drilling this deep requires a lot of preparation, starting from finding the best location, permitting and having a well thought out design. We are eager to get started though, and will be making detailed plans!