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Fracture permeability and seismic wave scattering –Poroelastic Linear-Slip Interface model for heterogeneous fractures Seiji Nakagawa and Larry R. Myer, Lawrence Berkeley National Laboratory, Berkeley, CA, USA Summary Schoenberg’s Linear-slip Interface (LSI) model for single, compliant, viscoelastic fractures has been extended to poroelastic fractures for predicting seismic wave scattering. However, this extended model results in no impact of the in-plane fracture permeability on the scattering. Recently, we proposed a variant of the LSI model considering the heterogeneity in the in-plane fracture properties. This modified model considers wave-induced, fracture-parallel fluid flow induced by passing seismic waves. The research discussed in this paper applies this new LSI model to heterogeneous fractures to examine when and how the permeability of a fracture is reflected in the scattering of seismic waves. From numerical simulations, we conclude that the heterogeneity in the fracture properties is essential for the scattering of seismic waves to be sensitive to the permeability of a fracture. Introduction Schoenberg originally formulated the Linear-Slip Interface (LSI) model for predicting the frequency- and compliance-dependent scattering of seismic waves, by a flat, two-dimensional fracture (Schoenberg, 1980). This original model is for a viscoelastic fracture and a background. The applicability of the model has been demonstrated by many laboratory experiments (e.g., Pyrak-Nolte et al. 1990; Myer et al., 1990; Hsu and Schoenberg, 1993). For examining the effect of pore fluids, poroelastic version of the models have been developed, for open fractures (Bakulin and Molotkov, 1997) and fractures clogged with gouge materials with a range of permeability (Nakagawa and Schoenberg, 2007). These poroelastic LSI models, however, predicted that the scattering of seismic waves are not affected by the in-plane (or fracture-parallel) permeability of a fracture, because no permeabililty terms appear in the models (Note that the “clogged-fracture” model predicts dependency on the out-of-plane [or fracture- normal] permeability of the fracture, owing to the gouge layer.) The primary reason for this apparent lack of sensitivity to permeability may be that these poroelastic LSI models assume a fracture with a homogeneous distribution of fracture properties including mechanical compliance, width (opening), fluid properties, and permeability. Heterogeneous distributions of these properties can result in increased local gradients of wave- induced fluid pressures, which can enhance the fluid flow within the fracture. (e.g., Dvorkin et al., 1994; Pride and Berryman, 2003ab)

Fracture permeability and seismic wave scattering—Poroelastic linear‐slip interface model for heterogeneous fractures