Theoretical calculation of dispersion and attenuation curves of deep-guided wave in viscoelastic media

SUMMARY The low-velocity layer confined by surrounding rocks deep in the subsurface acts as a seismic waveguide. The compressional (P) and shear (S) waves propagate in the waveguide are reflected on the top and bottom interface, constructively interfered with to formulate the deep-guided wave. Deep-guided wave has high-frequency contents and notable dispersive features. The dispersion represents the kinematics information and can be used to image the low-velocity structures. The Earth media not only shows elasticity but also attenuates seismic waves. This article presents a theoretical study of deep-guided wave propagation and dispersion analysis in viscoelastic media. We utilize the Thomson–Haskell propagator matrix method to theoretically calculate the phase velocity dispersion and attenuation curves of the deep-guided wave in viscoelastic media. We apply the staggered-grid finite-difference scheme to numerically simulate the elastic wavefield propagation in the shale layer for validation. We have conducted a sensitivity analysis of the dispersion and attenuation curves of the deep-guided wave with respect to different media parameters. The theoretical calculation of dispersion and attenuation curves of deep-guided wave opens the doors for the simultaneous inversion of S-wave velocity and quality factor of the low-velocity layer in the future. Deep-guided waves hold the potential for high-resolution imaging of hydrocarbon reservoirs, geothermal reservoirs, coal seams, saline aquifers and fault zones.