In this news item we have answered the other questions that were asked during the round of questions at the environmental permit information meeting about drilling on 26 July.
Are you missing something or do you have another question? Tell us by emailing info@geothermiedelft.nl
Fractures are naturally present in every substrate. Some of these faults have already formed during the deposition when the geological formation to be tapped was still on the surface. Now this formation lies at a depth of 2 km. The 'blue' fault on slide 14 is a fault surface in the Delft sandstone that does not continue into the 'overburden', i.e. the sealing layers above the reservoir. This fracture surface has been interpreted as pressure permeable and non-occlusive and assessed as extremely low risk. Nevertheless, both the production well and the injection well are placed on the same side of the fracture so that the direct water flow direction from the injection well to the production well does not cross the fracture surface.
Absolutely, investigating the presence of shallow gas is always part of the job package. The Pijnacker oil field is relatively far away and the best references in the vicinity are the Delft 07 and Delft 08 wells (see NLOG). These are hundreds of meters away and the well of Geothermie Delft is drilled exactly in between. We know from these wells that no shallow gas has been detected and that we have an absolute overpressure there with the drilling mud* weights used. This overpressure ensures that the drilling process remains stable and prevents reservoir fluids, such as salt water with dissolved gas, from entering the wellbore. We will therefore maintain a slightly higher mud weight for Geothermie Delft in order to maintain the high pressure.
*Drilling fluid or drilling mud: Drilling fluid is used during drilling. This is a mixture of water (or oil) with clay particles and possibly other substances. The drilling fluid has four functions:
The drilling company continuously measures the composition of the drilling fluid and adjusts it as necessary so that it can serve all functions and ensure safety during drilling.
The drilling will continue at a depth of about 1600 meters under the Yellow Chemistry building. There is no need to consider this as there is absolutely no interference even 100 meters away from the GTD drilling site. The activities at Yellow Chemistry can take place completely simultaneously without mutual hindrance. There is also continuous coordination with the BLVC (Accessibility, Liveability, Safety, Communication) coordinator of TU Delft about all parallel implementation projects on and around the site of the TU Delft Campus. This also includes construction traffic.
The sand layers a few hundred meters away will be pierced with an overpressure drilling mud. This drilling mud has a plastering effect and the overpressure also ensures that no liquids penetrate into the sand layers. As a result, there is no interaction with the contents of the reservoir. After a few days after the start of the drilling, a steel borehole casing (casing) is installed and cemented (the first layer of the double casing). This prevents the farmer's rinse from leaking. In the future, consideration will also be given to shallow heat storage, possibly using this reservoir via other boreholes. In that case, coordination must take place.
By placing the conductor as deep as possible, the shallow freshwater or brackish groundwater layers are physically separated from the production and injection well. In addition, the geothermal sector recently established an Industriesta
