Acoustic micro-lapses: A novel approach to characterizing attenuation

Abstract

Attenuation is observed experimentally using acoustic micro-lapses. This novel approach consists of synchronizing the shooting of two wavefields; the second, called Tracking Wave (TW) is to probe the stiffness oscillations occurring during the creep induced by the first wave, called Pilot Wave (PW). By computing EΔ_t, a quantity proportional to the energy difference between the two waves as function of phase shift, it is observed that for tight sandstone and aluminium samples, EΔ_t is constant, indicating that the medium responds elastically as expected. For Lucite and Berea sandstone EΔ_t depicts distinct maxima implying that TW senses the transitory perturbations induced by PW, confirming thus wave dissipation. To assess these results, quasi-static tests using two Heaviside functions show that upon the application of the second load, the composite creep compliance develops a strong discontinuity, which reveals the existence of two unrelaxed moduli; this explains the spectral differences between both waves.