Journal
GEOPHYSICAL JOURNAL INTERNATIONAL
Volume 197, Issue 1, Pages 636-641Publisher
OXFORD UNIV PRESS
DOI: 10.1093/gji/ggu018
Keywords
Geomechanics; Rheology and friction of fault zones; Fractures and faults
Categories
Funding
- French National research Agency (ANR) through the SEED programme (project FISIC) [ANR-11-0003-01]
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Fluid injection in deep sedimentary porous formations might induce shear reactivation of reservoir bounding faults. Here, we focus on 'blind' 1000-m-long normal faults (with shear displacement <= 10m), which can hardly be detected using conventional seismic surveys, but might potentially induce seismicity felt on surface. The influence of the dissymmetry in the internal structure of the fractured damage zone DZ is numerically investigated by using 2-D plane-strain finite-element simulations of a 1500-m-deep fluid injection into a porous reservoir. The problem is solved within the framework of fully saturated isothermal elasto-plastic porous media by both accounting for fault slip weakening and shear-induced degradation of fault core permeability. The numerical results show that the presence of a thick fractured hanging wall's DZ (with Young's modulus decreasing with the distance to the fault core due to the presence of fractures) strongly controls the magnitude M of the seismic event induced by the rupture. In the case modelled, M changed by more than 1.0 unit when the DZ thickness is varied from 5 to 50 m (M ranges from similar to 0.1 to similar to 1.5, i.e. from a 'low' to a 'low-to-moderate' seismicity activity). However, further extending DZ up to 90 m has little effect and the relationship reaches a quasi-horizontal plateau. This tendency is confirmed considering other initial conditions and injection scenarios. Finally, the presence of a thicker footwall DZ appears to lower the influence of hanging wall's DZ, but with lesser impact than the degree of fracturing.
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