HR: 09:30h
AN: S21A-07    [PDF]
TI: Seismic Frequency Attenuation and Fluid Motion
AU: Kumar, G
EM: gautam.kumar@lycos.com
AF: British Gas India Pvt. Ltd., 3rd Floor, Tower B, First India Place Sushant Lok - I Mehrauli - Gurgaon Road, Gurgaon, Del 110092 India
AU: Batzle, M L
EM: mbatzle@mines.edu
AF: Colorado School of Mines Geophysics Department, 1500 Illinois St, Golden, CO 80401 United States
AU: * Hofmann, R
EM: rhofmann@mines.edu
AF: Colorado School of Mines Geophysics Department, 1500 Illinois St, Golden, CO 80401 United States
AB: The relations among the different modes of attenuation (1/Qk, 1/Qp, 1/Qs, 1/Qe) are controlled by the mobility of the pore fluid within rocks. Attenuation covering the exploration seismic band (20 -1000 Hz) was derived at low amplitudes by measuring the phase angles between the applied stress and sample strain. Assuming that attenuation can be defined from the complex moduli as the ratio between imaginary part and real part.of the complex moduli., Winkler and Nur (1979) showed that one of three relations must hold: (1) 1/Qs $<$ 1/Qe $<$ 1/Qp $<$ 1/Qk; or (2) 1/Qs = 1/Qe = 1/Qp = 1/Qk; or (3) 1/Qs $>$ 1/Qe $>$ 1/Qp $>$ 1/Qk. The applicable relation is controlled by the compressional to shear velocity ratio or Poisson's ratio. In partially saturated rocks with high fluid mobility, 1/Qk is a maximum and 1/Qs is minimum (relation 1). At 100% liquid saturation with no fluid motion, 1/Qs is now the maximum and 1/Qk is the minimum (3). In contrast, for the same liquid saturated sample, if macroscopic fluid motion is permitted across an open boundary, the 1/Qk can again reach the maximum. However, the fluid mobility and attenuation mechanisms are strongly frequency dependent and interrelated. Thus, the scale of partial saturation or diffusion lengths and fluid mobility will control the attenuation relationships.
UR: http://crusher.mines.edu/Atten
DE: 5102 Acoustic properties
DE: 5144 Wave attenuation
DE: 5194 Instruments and techniques
DE: 5199 General or miscellaneous
SC: Seismology [S]
MN: 2003 Fall Meeting