In CCS wells, cyclic injection of cold CO₂ into the hot subsurface may lead to debonding between sealant and steel casing. We test how thermal cycling affects the sealing ability of five different types of sealant (S1 to S5) surrounding a simulated steel wellbore. We use cylindrical sealant samples with a stainless steel (AISI 316 L) pipe in the centre, cured at 150°C and 30 MPa for 28 days. Using 3 bar N₂ leak tests at room temperature, we test how much the sealant-steel interface leaks before and after thermal cycling under unconfined and confined (1.5 MPa) conditions. We also conduct push-off experiments using a 500 kN loading frame before and after. For the unconfined test, we place the sample on a custom-built jig, whereas for confined tests we have a similar assembly inside a conventional triaxial vessel. The samples are brought to 60°C. Subsequently, we inject 5°C water through the central pipe at 80 mL/min for 2 mins, and let the sample reheat for 12 mins. We repeat this 16 times. Afterwards, we allow the sample to cool to room temperature, and repeat the N₂ leak test in-situ. The results show that under unconfined conditions, the interface leaks more for all sealant types except S3. The key parameter controlling performance is the linear thermal expansion coefficient, where an expansion coefficient closer to that of steel indicates better performance. Under confinement, all sealant types perform better post-thermal cycling, due to the prolonged exposure to confining pressure.

The TU Delft campus geothermal project has joint objectives of research and commercial thermal energy production. It has been developed and will be operated by the Geothermie Delft (GTD) consortium, a commercial cooperation between TU Delft, Aardyn, EBN and Shell Geothermal. This report gives an overview of the research activities that have been carried out during the implementation of the doublet drilling the wells DEL-GT-01 and DEL-GT-02, and the sidetracks DEL-GT-02-S1 and DEL-GT-02-S2 in the period June - December 2023. The research programme and related operations during the installation of the campus geothermal wells have been led by the scientific team of TU Delft department of Geoscience and Engineering. The project is part of the national research infrastructure for solid Earth science (https://epos-nl.nl/), and offers the possibility to do state of the art research on an operating geothermal system.
The main research activities that were carried out during the implementation of the geothermal wells included rock sampling in the form of a detailed drill cutting sampling set, full cores and sidewall cores of the caprock and the geothermal reservoir, open-hole logging of the reservoir formations and the installation of a fibre optic cable in the producer (still to be carried out).
Overall, the following samples and data were collected as part of the scientific programme:
- 15m of 4”core from the direct caprock of the producer reservoir section
- 71m of 4”core from the reservoir section of the producer
- 78 sidewall cores from the injector reservoir section
- 2400 cutting samples
- 3000m of open-hole and closed-hole logging data
Details of these activities can be found in the report and the related appendices. All data presented in this report have been published via TU Delft institutional data repository and can be found online as part of the data collection associated with the research programme of the project: Geothermal Project on TU Delft Campus Collection at https://doi.org/10.4121/85b3725b-80fa-4b0b-9db2-475bfd8f0265.

As part of the Synergetic Utilisation of CO (Formula presented.) storage Coupled with geothermal EnErgy Deployment project, investigating CO (Formula presented.) reinjection with different seismic methods, both passive and active seismic surveys have been conducted at the geothermal power plant at Hellisheiði, Iceland. During the 2021 survey, two geophone lines recorded noise for a week. We process the passive-source data with seismic interferometry to image the subsurface structure around the CarbFix2 reinjection reservoir. To improve image quality, we perform an illumination analysis to select only noise panels dominated by body-wave energy. The results show that most noise panels are dominated by air-wave energy arriving from the direction of the power plant. We use panels with a near-vertical incidence to create a zero-offset image and a larger selection of body-wave-dominated panels to create virtual common-shot gathers. We process the gathers with a simple reflection seismology processing workflow to obtain stacked images. The zero-offset images show a relatively lower signal-to-noise ratio and only horizontal reflectors. The stacked images show slightly dipping reflectors and possibly lateral amplitude variations around the expected injection region. This could indicate a region of interest for future research into the reinjection reservoir.