HR: 17:50h
AN: NS54A-07 [Abstracts]
TI: Analysis of mesoscopic attenuation in gas-hydrate bearing sediments
AU: * Rubino, J G
EM: grubino@fcaglp.unlp.edu.ar
AF: CONICET, Departamento de Geofisica Aplicada, Facultad de Ciencias Astronómicas y
Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, Bue 1900, Argentina
AU: Ravazzoli, C L
EM: claudia@fcaglp.unlp.edu.ar
AF: CONICET, Departamento de Geofisica Aplicada, Facultad de Ciencias Astronómicas y
Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, Bue 1900, Argentina
AU: Santos, J E
EM: santos@fcaglp.unlp.edu.ar
AF: CONICET, Departamento de Geofisica Aplicada, Facultad de Ciencias Astronómicas y
Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque s/n, La Plata, Bue 1900, Argentina
AU: Santos, J E
EM: santos@fcaglp.unlp.edu.ar
AF: Department of Mathematics, Purdue University, 150 N. University Street, West Lafayette, IN
47907-2067, United States
AB:
Several authors have shown that seismic wave attenuation combined with seismic velocities constitute a
useful geophysical tool to infer the presence and amounts of gas hydrates lying in the pore space of the
sediments.
However, it is still not fully understood the loss mechanism associated to the presence of the hydrates, and most
of the works dealing with this problem focuse on macroscopic fluid flow, friction between hydrates and sediment
matrix and squirt flow.
It is well known that an important cause of the attenuation levels observed in seismic data from some
sedimentary regions is the mesoscopic loss mechanism, caused by heterogeneities
in the rock and fluid properties greater than the pore size but much smaller than the wavelengths.
In order to analyze this effect in heterogeneous gas-hydrate bearing sediments, we developed a finite-element
procedure to obtain the effective complex modulus of an heterogeneous porous material containing gas hydrates
in its pore space using compressibility tests at different oscillatory frequencies in the seismic range.
The complex modulus were obtained by solving Biot's equations of motion in the space-frequency domain with
appropriate boundary conditions representing a
gedanken laboratory experiment measuring the complex volume change of a representative sample of
heterogeneous bulk material. This complex modulus in turn allowed us to obtain the corresponding effective
phase velocity and quality factor for each frequency and spatial gas hydrate distribution.
Physical parameters taken from the Mallik 5L-38 Gas Hydrate Research well (Mackenzie Delta, Canada) were
used to analyze the mesoscopic effects in realistic hydrated sediments.
DE: 0545 Modeling (4255)
DE: 3004 Gas and hydrate systems
DE: 5102 Acoustic properties
DE: 5144 Wave attenuation
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly