HR: 0800h
AN: NS31B-0398    [Abstracts]
TI: Offset Dependence of Effective Q (Scattering and Intrinsic) Attenuation: Measurements from Permanent Down-hole Geophones
AU: * Mangriotis, M
EM: mdaphne@berkeley.edu
AF: University of California at Berkeley, 415 Davis Hall, Berkeley, CA 94720, United States
AU: Rector, J
EM: jwrector@lbl.gov
AF: University of California at Berkeley, 415 Davis Hall, Berkeley, CA 94720, United States
AU: Herkenhoff, F
EM: efhe@chevron.com
AF: Chevron Energy Technology Company, Building D, 6001 Bollinger Cyn Rd, San Ramon, CA 94583, United States
AU: Nihei, K
EM: knih@chevron.com
AF: Chevron Energy Technology Company, Building D, 6001 Bollinger Cyn Rd, San Ramon, CA 94583, United States
AB: Attenuation (Q) profiles were determined from a VSP study of a well in the Lawrence Livermore National Lab facility using permanent down-hole geophones and a vertical elastic generator source. We used the zero-offset data to determine the interval velocity profile, and combined gamma ray, and other log information to model the density and P- and S- wave velocity profile. From these profiles we generated synthetic offset data using a 2- dimensional elastic finite difference model assuming laterally homogeneous layers and compared the attenuation measured from the synthetic data with the attenuation measured from the real data. The attenuation of the zero-offset synthetic data is slightly larger than the attenuation predicted by the O"Doherty and Anstey formula for 1-D scattering, whereas the attenuation of the zero-offset real data is substantially greater than the attenuation of the synthetic data, and the amplitudes predicted by the ODA approach. We modeled the angle-dependent scattering Q with an empirical function that captures the behavior of the offset synthetic data, and adjusted the amplitudes of the real data to examine whether the intrinsic Q is laterally homogeneous. We then generated additional viscoelastic models for a Voigt and Standard Linear Solid Q to match the amplitude and phase components in the real data. We computed horizontal space average Q factors at different depth intervals and concluded that the primary source of attenuation in our location is intrinsic.
DE: 0935 Seismic methods (3025, 7294)
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting