HR: 17:30h
AN: S12G-07    [PDF]
TI: Separating Scattering from Intrinsic Attenuation
AU: * van Wijk, K
EM: kasper@acoustics.mines.edu
AF: physical acoustics laboratory, dept. of GP, CSM, 1500 illinois street, golden, CO 80401 United States
AU: Scales, J A
EM: jscales@acoustics.mines.edu
AF: physical acoustics laboratory, dept. of GP, CSM, 1500 illinois street, golden, CO 80401 United States
AB: The subsurface appears disordered at all length-scales. Therefore, wave propatation at seismic or ultrasonic frequencies is subject to complicated scatterings. A pulse propagating in the subsurface loses energy at each scattering off an impedance contrast, but also decreases in amplitude as the impulse interacts with fluids in the rock. We call the latter non-elastic effect "intrinsic Q", while the former is "scattering Q". It is often the fluids in the rocks that are of interest, but conventional reflection and transmission of the incident pulse only cannot deceipher the individual components of Q due to scattering and fluid movement in the pore-space. We present an approach that can unravel these two mechanisms, allowing a separate estimate of absorption. This method treats the propagation of the average intensity in the framework of radiative transfer (RT); the arrival of (what is left of) the incident pulse is modeled as the coherent energy, whereas the later arriving multiply scattered events form the incoherent intensity. The coherent pulse decays exponentially due to a combination of scattering and absorption, and so does the incoherent intensity. However, multiple scattering can re-direct energy back to the receiver, supplying a gain-term at later times that makes up the incoherent intensity. Strictly speaking, one can invert for scattering and absorption from the intensity at late times only, often modeled with the late-time equivalent of RT, diffusion. However, we will show that fitting both early- and late-time signal with RT constrains absorption and scattering constants more rigorously. These ideas are illustrated by laboratory and sonic-logging measurements.
DE: 0915 Downhole methods
DE: 3210 Modeling
DE: 5144 Wave attenuation
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting