Permeability Evolution During Shear Zone Initiation in Low-Porosity Rocks

Permeability Evolution During Shear Zone Initiation in Low-Porosity Rocks

Kluge, C. (TU Delft Reservoir Engineering; Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences)
Blöcher, Guido (Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences)
Barnhoorn, A. (TU Delft Applied Geophysics and Petrophysics)
Schmittbuhl, Jean (Institut de Physique du Globe de Strasbourg)
Bruhn, D.F. (TU Delft Reservoir Engineering; Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences)

2021

Using an innovative experimental set-up (Punch-Through Shear test), we initiated a shear zone (microfault) in Flechtingen sandstone and Odenwald granite under in situ reservoir conditions while monitoring permeability and fracture dilation evolution. The shear zone, which has a cylindrical geometry, is produced by a self-designed piston assembly that punches down the inner part of the sample. Permeability and fracture dilation were measured for the entire duration of the experiment. After the shear zone generation, the imposed shear displacement was increased to 1.2 mm and pore pressure changes of ± 5 or ± 10 MPa were applied cyclically to simulate injection and production scenarios. Thin sections and image analysis tools were used to identify microstructural features of the shear zone. The geometry of the shear zone is shown to follow a self-affine scaling invariance, similar to the fracture surface roughness. The permeability evolution related to the onset of the fracture zone is different for both rocks: almost no enhancement for the Flechtingen sandstone and an increase of more than 2 orders of magnitude for the Odenwald granite. Further shear displacement resulted in a slight increase in permeability. A fault compaction is observed after shear relaxation which is associated to a permeability decrease by a factor more than 3. Permeability changes during pressure cycling are reversible when varying the effective pressure. The difference in permeability enhancement between the sandstone and the granite is related to the larger width of the shear zones.

Fault architecture
Fracture permeability
Granite
Microfault
Microstructure
Roughness
Sandstone

http://resolver.tudelft.nl/uuid:a7ffc180-584c-45dc-a1d7-0a727f5c92dd

https://doi.org/10.1007/s00603-020-02356-0

0723-2632

Rock Mechanics and Rock Engineering, 54 (10), 5221-5244

Institutional Repository

journal article

© 2021 C. Kluge, Guido Blöcher, A. Barnhoorn, Jean Schmittbuhl, D.F. Bruhn