Permeability Variations Associated With Fault Reactivation in a Claystone Formation Investigated by Field Experiments and Numerical Simulations

Journal Article · 31 January 2018 · Journal of Geophysical Research. Solid Earth

DOI: https://doi.org/10.1002/2017JB015149 · OSTI ID:1461130

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

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1. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Energy Geoscience Division
2. Federal Office of Topography, Swisstopo, Wabern (Switzerland)

We studied the relation between rupture and changes in permeability within a fault zone intersecting the Opalinus Clay formation at 300 m depth in the Mont Terri Underground Research Laboratory (Switzerland). A series of water injection experiments were performed in a borehole straddle interval set within the damage zone of the main fault. A three-component displacement sensor allowed an estimation of the displacement of a minor fault plane reactivated during a succession of step rate pressure tests. The experiment reveals that the fault hydromechanical (HM) behavior is different from one test to the other with varying pressure levels needed to trigger rupture and different slip behavior under similar pressure conditions. Numerical simulations were performed to better understand the reason for such different behavior and to investigate the relation between rupture nucleation, permeability change, pressure diffusion, and rupture propagation. Here, our main findings are as follows: (i) a rate frictional law and a rate-and-state permeability law can reproduce the first test, but it appears that the rate constitutive parameters must be pressure dependent to reproduce the complex HM behavior observed during the successive injection tests; (ii) almost similar ruptures can create or destroy the fluid diffusion pathways; (iii) a too high or too low diffusivity created by the main rupture prevents secondary rupture events from occurring whereas “intermediate” diffusivity favors the nucleation of a secondary rupture associated with the fluid diffusion. However, because rupture may in certain cases destroy permeability, this succession of ruptures may not necessarily create a continuous hydraulic pathway.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE), Building Technologies Office (EE-5B); Japanese Atomic Energy Agency (JAEA); Swiss Federal Nuclear Safety Inspectorate (ENSI)
• Grant/Contract Number: AC02-05CH11231
• OSTI ID: 1461130
• Alternate ID(s): OSTI ID: 1422025
• Journal Information: Journal of Geophysical Research. Solid Earth, Journal Name: Journal of Geophysical Research. Solid Earth Journal Issue: 2 Vol. 123; ISSN 2169-9313
• Publisher: American Geophysical UnionCopyright Statement
• Country of Publication: United States
• Language: English