Sensitivity of coda wave interferometry to fluid migration through rock

Area of Science:

• Acoustics
• Geophysics
• Materials Science

Background:

• Sound speed in porous media is sensitive to fluid composition.
• Fluid substitution alters acoustic properties, impacting wave propagation.
• Understanding fluid dynamics in porous materials is crucial for various applications.

Purpose of the Study:

• To demonstrate coda wave interferometry's capability in detecting subtle sound speed variations.
• To investigate the resolution of fluid motion detection using coda wave interferometry.
• To identify the optimal waveform time for maximum sensitivity to fluid displacements.

Main Methods:

• Application of coda wave interferometry to analyze acoustic wave propagation in porous media.
• Mathematical modeling of sound speed changes due to fluid substitution.
• Derivation of a scaling relationship to quantify fluid motion resolution.

Main Results:

• Coda wave interferometry successfully senses minute local sound speed changes.
• Fluid motion resolution is governed by a scaling relationship involving waveform time, wavelength, and attenuation.
• A temporal optimum for sensitivity to fluid displacement exists, contrary to the assumption that later arrivals are always best.

Conclusions:

• Coda wave interferometry offers high resolution for detecting small fluid displacements in porous media.
• The study reveals an optimal time window for maximizing sensitivity, challenging conventional understanding.
• The findings provide a physical basis for optimizing fluid motion monitoring in geophysical and material science contexts.