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Strain and Flow Pathways in a Shale Fault Zone: An In-Situ Test of Fault Seal Integrity

Abstract : A series of small scale (decametric) injection tests were performed in a small fault at IRSN Tournemire underground laboratory in Toarcian shales. Pressure, induced strains and flow rate were monitored at the injection borehole. Monitoring systems comprising strain sensors and a resistivity streamer were installed in observation boreholes within the fluid invaded zone. A micro-seismic network was also deployed. This experiment shows complex interactions between flow and strain as both appear to be distributed between major discontinuities and the fracture network in the damage and core zones. Permeability variations can be approximated as exponential functions of fluid pressure, with different coefficients below and above a threshold, defining the Fracture Opening Pressure. Hydraulic opening is typically associated with dilatant shearing of fractures. However, the associated strain appears small and largely reversible. Rupture on the main fault plane is triggered after several hours of injection, resulting in a permanent change of flow pathways and flow rate. Numerical modeling based on these experimental results suggest fluid channeling along a fault zone could occur in the subcritical Coulomb regime without fault activation at the larger scale.
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P. Henry, Y. Guglielmi, C. Gout, R. Castilla, P. Dick, et al.. Strain and Flow Pathways in a Shale Fault Zone: An In-Situ Test of Fault Seal Integrity. Fifth International Conference on Fault and Top Seals 2019, EAGE, 2019, Palermo, Italy. ⟨10.3997/2214-4609.201902318⟩. ⟨hal-02391332⟩

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