New borehole-based techniques for in situ stress measurement and related thermo-hydro-mechanical processes

Accurate in situ stress characterization is essential for predicting the subsurface response to interventions such as underground construction, fluid injection, and fluid extraction. At depths of 2–5 km, which are typical of many such projects, the stress field is often heterogeneous and influenced by complex geological features. This makes reliable stress measurement both operationally critical and technically challenging. Borehole stability is another key concern, as deep boreholes are prone to stress-induced deformations such as breakouts that can damage equipment, impede drilling, and even lead to borehole collapse.

We present results and ongoing developments from two projects focused on novel in situ stress measurement techniques and thermo-hydro-mechanical processes around boreholes. These projects are based on experiments conducted at the Bedretto Underground Laboratory (BedrettoLab) in Switzerland (Ma et al., 2022). The BedrettoLab offers multiple boreholes, up to 400 m in length, located within a fractured granitic rock mass with an overburden of more than 1000 m.

The first project developed an improved technique to estimate the full stress tensor by inverting three-dimensional displacement data obtained during fluid injections in isolated borehole intervals (Bröker et al., 2025). A total of eleven test intervals were investigated, with displacements measured using a SIMFIP (Step-rate Injection Method for Fracture In situ Properties) probe. The results yield a complete stress profile obtained along approximately 60 m of an inclined borehole, revealing significant stress heterogeneity and rotations around an intersected fault zone.

In the second project, we developed a novel borehole probe to investigate the formation of thermally induced breakouts, which are strongly controlled by the in situ stress field. The probe can heat a packed-off borehole section while measuring borehole wall displacement. After extensive calibration in the laboratory, the probe was deployed in the BedrettoLab, and three in situ heating tests were successfully conducted up to 140 °C. Although no borehole breakouts were induced, the experiments provide valuable insight into thermo-hydro-mechanical coupling at borehole walls and its role in breakout initiation and borehole stability.

References:

Bröker, K., Guglielmi, Y., Soom, F., Cook, P., Hertrich, M., & Valley, B. (2025). In situ quantification of fracture slip induced by hydraulic injections in a deep borehole: A comparison of two different borehole techniques. Submitted to IJRMMS. https://doi.org/10.2139/ssrn.5967430

Ma, X., Hertrich, M., Amann, F., Bröker, K., Gholizadeh Doonechaly, N., Gischig, V., Hochreutener, R., Kästli, P., Krietsch, H., Marti, M., Nägeli, B., Nejati, M., Obermann, A., Plenkers, K., Rinaldi, A. P., Shakas, A., Villiger, L., Wenning, Q., Zappone, A., et al. (2022). Multi-disciplinary characterizations of the BedrettoLab – a new underground geoscience research facility. Solid Earth, 13(2), 301–322. https://doi.org/10.5194/se-13-301-2022