Fluid effect on wave propagation in heterogeneous porous media

Fluid effect on wave propagation in heterogeneous porous media

Vogelaar, B.B.S.A.

Wapenaar, C.P.A. (promotor)

Civil Engineering and Geosciences

2009-03-18

Acoustic wave propagation through porous media is affected by the properties of the pore fluid and the matrix material. The acoustic velocity is extensively used for imaging of subsurface strata, and to predict petrophysical properties. In contrast, the attenuation (loss of wave energy) is not routinely used. This thesis reports the influence of fluid inhomogeneities (gas bubbles) on wave attenuation in fluid-saturated porous media. The underestimation of Biot-attenuation is due to heterogeneities on the microscale (microcracks in the grains or at the grain contacts) and on the mesoscale in the frame (e.g., interbedded shales) and the fluid (e.g., gas bubbles or gas layers). Mesoscopic inhomogeneities are described in local pressure equilibration models by local fluid flow. Applying the Rayleigh-Plesset-Biot model to literature data of resonant bar experiments on rock samples at frequencies from 0.6 to 6 kHz, a very good match between the reported and predicted attenuation was found. Using a gas-injection technique, a single bubble was created in an oil-saturated porous sample. Using Spectral Ratio Data Analysis, it was found that in this case the patchy saturation model gives a better prediction at 500 kHz. Differential Acoustic Resonance Spectroscopy (DARS) measurements on 45 natural rocks and artificial porous samples gave a good agreement with the Gassmann modulus for sealed porous samples. For open-pore samples the DARS modulus is governed by the relative fluid motion at the outer wall.

wave propagation
velocity
attenuation
patchy saturation
dars

http://resolver.tudelft.nl/uuid:1d8967a9-cd4f-49ae-ac77-203c51c33fae

9789090240510

Institutional Repository

doctoral thesis

(c) 2009 Vogelaar, B.B.S.A.