Geothermal Research Well on TU Delft Campus

A fibre optic cable will be installed together with the ESP. The cable is currently manufactured by Halliburton and expected to be deployed to Delft in Q2 2025.

Fibre requirements 2 x Single Mode (SM) fibre for pressure measurements 2 x Single Mode (SM) fibre for acoustic measurements Data requirements Pressure: Pressure gauges connected to a single-mode (SM) fibre provides a Distributed Pressure Sensing (DPS) system.

• Temperature: Acquired using a single-mode (SM) fibre based on Brillouin Scattering.
• Acoustics: Distributed Acoustic Sensing (DAS) through a single-mode (SM) fibre.
• Cable specifications:

All the optical fibres will be placed inside a Fibre in Metal Tube (FIMT). This FIMT is filled with Sepigel and will accommodate the Extra Fibre Length (EFL). This EFL ensure that the fibres will not break in case the cable stretches. The FIMT is placed inside a stainless steel tube (Tubing Encapsulated Fibre – TEF) with an OD of 4mm. The stainless steel tube is in theory the outside of the FO cable. In order to protect the cable, several additional components are included.

This local monitoring network has been equipped with optical fibres which connect the boreholes laterally and are also placed downhole. Fibre-optic cables were installed in shallow trenches, linking the two shallow boreholes DAPGEO-02-01B, DAPGEO02-02B and the central borehole DAPGEO-02 (200 m). DAS cable: one straight and one helically wound fibre.

The campus geothermal project consists of a doublet targeting the early Cretaceous Delft sandstone formation. The target reservoir location is situated within a syncline bounded to the south-west by a seismically-inactive fault, at approximately 1-km distance, and to the north-east by another seismically-inactive fault, at approximately 4-km distance from the surface location.

Both wells are deviated to north and east-northeast, respectively, such that they move away from the closer fault and target a deeper (hotter) portion of the reservoir. To the east and north-east of the reservoir are two other geothermal projects that serve to provide heat mainly to greenhouses, highlighting the proximity and potential of interaction of geothermal projects.

The Multi-Purpose Research Borehole DAPGEO-02 consists of 4 boreholes:

• One central borehole with a depth of 499 m
• One 200 m deep borehole in the close vicinity (~12 m distance) of the central location
• Two 50 m deep boreholes located further away (~100 m distance) from the central location.

The two 50 m boreholes (DAPGEO-02-01B, DAPGEO-02-02B) are used for seismic monitoring, equipped with geophones and fibre-optic cables. Geophones were installed in the multipurpose borehole at 440 and 490 m depth.

Three-component accelerometer install at surface DAPGEO-02