HR: 0830h
AN: S41A-11    [Abstracts]
TI: Converted-wave PS arrivals in tilted TI media: Analysis of ray-paths and amplitudes
AU: * Ramos-Martinez, J
EM: jrmartin@imp.mx
AF: Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152 Col. San Bartolo Atepehuacan, Mexico City, D.F 07730 Mexico
AU: Calderon-Macias, C
EM: ccaldero@imp.mx
AF: Instituto Mexicano del Petroleo, Eje Central Lazaro Cardenas 152 Col. San Bartolo Atepehuacan, Mexico City, D.F 07730 Mexico
AB: Converted-waves, i.e., downgoing P-waves that convert upon reflection to S-waves, excited by a compressional source and recorded by horizontal geophones provide a measure of media properties that relate to rock type and fluid saturation. Other uses that have arisen from measuring, analyzing and interpreting PS-waves, include improved structural imaging in formations with occurrence of gas and analysis of seismic anisotropy for estimating fracture density and orientation. Addressing anisotropy in the seismic processing flow is paramount due to the strong influence of this phenomenon in the wave path. Furthermore, analyses of both traveltimes and amplitudes that include anisotropic parameters provide a better picture of the subsurface. Anisotropy types used to describe common geologic scenarios include vertical and horizontal transversely isotropy (VTI and HTI, respectively). Presence of horizontal shale formations is a common cause of the VTI type, while a single vertical fracture system is a typical example of the HTI. Another degree of complexity is to consider a tilted symmetry axis corresponding to a formation with thin layers that are dipping, or the presence of non-vertical fractures. These media, described as tilted TI, have important observable effects on the converted-wave arrivals: i) asymmetry of the wave-path; ii) shear-wave splitting; and iii) non-zero amplitudes at zero offset. Based on numerical modeling, effects of the tilt in the simmetry axis on arrival times, travel path, and amplitudes of the converted waves are analyzed. Ultimate objectives of the work include quantifying these effects on converted-wave data processing, and investigating the reflected wavefield signature for retrieving tilt angle in situations where the stress field induces thin layering or fractures with a tilted symmetry axis.
DE: 0900 EXPLORATION GEOPHYSICS
DE: 0902 Computational methods, seismic
DE: 0910 Data processing
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2005 Joint Assembly