Estimating perturbed stress from 3-D borehole displacements induced by fluid injection in fractured or faulted shales

Journal Article · 03 March 2020 · Geophysical Journal International

DOI: https://doi.org/10.1093/gji/ggaa103 · OSTI ID:1605301

Guglielmi, Yves ^[1]; Nussbaum, Christophe ^[2]; Rutqvist, Jonny ^[1]; Cappa, Frédéric ^[3]; Jeanne, Pierre ^[1]; Birkholzer, Jens ^[1]

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1. Lawrence Berkeley National Laboratory, Energy Geosciences Division, Berkeley, CA 94720, USA
2. Federal Office of Topography, Swisstopo, Seftigenstrasse 264, CH-3084 Wabern, Switzerland
3. Lawrence Berkeley National Laboratory, Energy Geosciences Division, Berkeley, CA 94720, USA, Université Côte d'Azur, CNRS, Observatoire de la Côte d'Azur, IRD, Géoazur, Nice, France, Institut Universitaire de France, Paris, France

SUMMARY Hydrofracturing stress measurements in fractured and anisotropic shales are notoriously difficult, because opening of existing geological features tends to prevent the creation of a pure hydraulic fracture perpendicular to the least compressive principal stress. Here we show how adding 3-D borehole-displacement measurements while conducting the hydraulic injection test helps to better constrain the principal stress orientations and magnitudes. We developed a 3-D fully coupled hydromechanical numerical model to analyse the displacement, fluid pressure and injection flow-rate data measured during an injection pressure-step-rate test conducted to activate a faulted borehole interval in the Mont Terri Opalinus Clay (Switzerland). We find that injected fluids can only penetrate the fault when it is at or above the Coulomb failure pressure. Borehole displacement orientations are sensitive to a ∼15° variation in the stress–tensor orientation and a 1 MPa stress magnitude variation. Although some dispersion occurs while rupture is propagating along the fault plane ∼4 m away from the borehole, the maximum density of displacement orientations consistently informs about the stress orientation. Thus, an extended injection step-rate approach coupled with an accurate in situ measurement of the borehole wall displacements can be used to better constrain the local stress field perturbations in fractured shales and in heterogeneous rock in general.

• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• Grant/Contract Number: DEAC02-05CH11231
• OSTI ID: 1605301
• Journal Information: Geophysical Journal International, Journal Name: Geophysical Journal International Vol. 221 Journal Issue: 3; ISSN 0956-540X
• Publisher: Oxford University PressCopyright Statement
• Country of Publication: United Kingdom
• Language: English