A field test on the hydromechanical behaviour of flowing and nonflowing fractures in the 2.5 km COSC-1 borehole in crystalline rock, Sweden
(2025) In Hydrogeology Journal 33(2). p.425-448- Abstract
Understanding the initiation, propagation and evolution of water injection-induced fractures is essential for geo-energy applications. Hydromechanical stimulation experiments were conducted in a deep borehole drilled into crystalline bedrock to gain insights into these processes, involving simultaneous in-situ measurements of three-dimensional fracture displacements, injection flow rates, and water pressure in 2.4-m isolated borehole sections at 500-m depth. Three distinct sections were tested in the COSC-1 borehole (Sweden): a section of intact rock, a section with a hydraulically conductive fracture and a section with nonconductive fractures. Acoustic televiewer measurements conducted before and after the experiments confirmed the... (More)
Understanding the initiation, propagation and evolution of water injection-induced fractures is essential for geo-energy applications. Hydromechanical stimulation experiments were conducted in a deep borehole drilled into crystalline bedrock to gain insights into these processes, involving simultaneous in-situ measurements of three-dimensional fracture displacements, injection flow rates, and water pressure in 2.4-m isolated borehole sections at 500-m depth. Three distinct sections were tested in the COSC-1 borehole (Sweden): a section of intact rock, a section with a hydraulically conductive fracture and a section with nonconductive fractures. Acoustic televiewer measurements conducted before and after the experiments confirmed the generation of new fractures. Accurate positioning of measurement tools was ensured through gamma log profiling and an innovative FFEC-based method for detecting flowing fractures. The tests revealed several transitional pressure values associated with mechanical events, with intact rock requiring the highest pressure to induce fracturing, followed by the nonconductive fracture section and the initially conductive fracture section. Following fluid injection, transient pressure decays were observed that were associated with leakage from newly generated fractures, providing insights into fracture behaviour under stimulation. Vertical displacements were predominant across the different tests, with measured displacements typically ranging from 10 to 100 µm. Fracture activation modes primarily involved the normal opening of subhorizontal fractures that were parallel to the metamorphic foliation, with some irreversible slip at higher pressures. However, a more complex scenario was observed in the test interval with previously nonconductive fractures, involving competition between the opening of subhorizontal fractures and reverse shearing of a steeply dipping fracture.
(Less)
- author
- organization
- publishing date
- 2025-03
- type
- Contribution to journal
- publication status
- published
- subject
- keywords
- Borehole instruments, Deep fracture hydrogeology, Fractured rocks, Hydrogeomechanics, Sweden
- in
- Hydrogeology Journal
- volume
- 33
- issue
- 2
- pages
- 24 pages
- publisher
- Springer Nature
- external identifiers
-
- scopus:105003306358
- ISSN
- 1431-2174
- DOI
- 10.1007/s10040-025-02886-3
- language
- English
- LU publication?
- yes
- id
- bc7e7fcf-f35d-4e13-a48d-63882cc843b0
- date added to LUP
- 2026-01-09 13:11:29
- date last changed
- 2026-01-09 13:12:34
@article{bc7e7fcf-f35d-4e13-a48d-63882cc843b0,
abstract = {{<p>Understanding the initiation, propagation and evolution of water injection-induced fractures is essential for geo-energy applications. Hydromechanical stimulation experiments were conducted in a deep borehole drilled into crystalline bedrock to gain insights into these processes, involving simultaneous in-situ measurements of three-dimensional fracture displacements, injection flow rates, and water pressure in 2.4-m isolated borehole sections at 500-m depth. Three distinct sections were tested in the COSC-1 borehole (Sweden): a section of intact rock, a section with a hydraulically conductive fracture and a section with nonconductive fractures. Acoustic televiewer measurements conducted before and after the experiments confirmed the generation of new fractures. Accurate positioning of measurement tools was ensured through gamma log profiling and an innovative FFEC-based method for detecting flowing fractures. The tests revealed several transitional pressure values associated with mechanical events, with intact rock requiring the highest pressure to induce fracturing, followed by the nonconductive fracture section and the initially conductive fracture section. Following fluid injection, transient pressure decays were observed that were associated with leakage from newly generated fractures, providing insights into fracture behaviour under stimulation. Vertical displacements were predominant across the different tests, with measured displacements typically ranging from 10 to 100 µm. Fracture activation modes primarily involved the normal opening of subhorizontal fractures that were parallel to the metamorphic foliation, with some irreversible slip at higher pressures. However, a more complex scenario was observed in the test interval with previously nonconductive fractures, involving competition between the opening of subhorizontal fractures and reverse shearing of a steeply dipping fracture.</p>}},
author = {{Guglielmi, Yves and Niemi, Auli and Tsang, Chin Fu and Dobson, Patrick and Cook, Paul and Juhlin, Christopher and Dessirier, Benoît and Tatomir, Alexandru and Basirat, Farzad and Lorenz, Henning and Rosberg, Jan Erik and Lundberg, Emil and Almqvist, Bjarne and Roberts, Roland}},
issn = {{1431-2174}},
keywords = {{Borehole instruments; Deep fracture hydrogeology; Fractured rocks; Hydrogeomechanics; Sweden}},
language = {{eng}},
number = {{2}},
pages = {{425--448}},
publisher = {{Springer Nature}},
series = {{Hydrogeology Journal}},
title = {{A field test on the hydromechanical behaviour of flowing and nonflowing fractures in the 2.5 km COSC-1 borehole in crystalline rock, Sweden}},
url = {{http://dx.doi.org/10.1007/s10040-025-02886-3}},
doi = {{10.1007/s10040-025-02886-3}},
volume = {{33}},
year = {{2025}},
}