Seismic Spectral Modification by Resonant Oscillation of Liquid Drops in Pores

Low frequency passive seismic spectroscopy (LFPSS) posits that hydrocarbons in a reservoir modify the spectrum of a passing seismic wave such that it induces a resonance behavior in the approximate range of 1 – 10 Hz. The mechanism for this effect has never been adequately specified, but one theory states that the resonance of oscillating oil drops due to capillarity somehow induces a resonance in the seismic wave spectrum as well, where the spectral peak is at the oil drop resonant frequency, ω0. In this paper, we consider the spectral modification of a seismic wave by resonating fluid drops. We limit ourselves to the case of longitudinal vibration of elongated pores, which is the case of pore motion generally considered by LFPSS proponents. From our analysis, we find that the effect on the seismic spectrum of oscillating drops does not support the LFPSS hypothesis, irrespective of the magnitude of the resonant frequency.