HR: 0830h
AN: S41C-02    [Abstracts]
TI: Spectral element modeling of fault-plane reflections arising from fluid pressure distributions
AU: * Haney, M M
EM: mmhaney@sandia.gov
AF: Sandia National Laboratories, Geophysical Technology Sandia National Laboratories P.O. Box 5800 MS-0750, Albuquerque, NM 87185 United States
AU: Snieder, R
EM: rsnieder@mines.edu
AF: Colorado School of Mines, Department of Geophysics Colorado School of Mines, Golden, CO 80401 United States
AU: Ampuero, J
EM: ampuero@erdw.ethz.ch
AF: ETH Honggerberg, Institute of Geophysics Seismology and Geodynamics ETH Honggerberg (HPP), Zurich, CH-8093 Switzerland
AB: In order to better understand the origin of fault-plane reflections in compacting sedimentary basins, we have numerically modeled the elastic wave equation via the spectral element method (SEM) for several different fault models. Using well log data from the South Eugene Island field, offshore Louisiana, we derive empirical relationships between the elastic parameters (e.g., P-wave velocity and density) and the effective-stress along both normal compaction and unloading paths. These empirical relationships guide the numerical modeling and allow us to investigate how differences in fluid pressure modify the elastic wavefield. We chose to simulate the elastic wave equation via SEM since irregular model geometries can be accommodated and slip boundary conditions at an interface, such as a fault or fracture, are implemented naturally. The method of including a slip interface retains the desirable qualities of SEM in that it is explicit in time and does not require the inversion of a large matrix. We perform a complete numerical study by forward modeling shot gathers over a realistically-sized Earth model using SEM and processing the simulated data to reconstruct post-stack time-migrated images of the kind that are routinely interpreted in the seismic industry. We dip filter the seismic images to highlight the fault-plane reflections prior to making amplitude maps on the fault plane. With these amplitude maps, we compare the reflectivity from the different models to diagnose which contributes most to the observed fault reflectivity. To lend physical meaning to the value of compliance for a slipping fault, we propose an equivalent-layer model under the assumption of weak scattering. This allows us to use the empirical relationships between density, velocity, and effective stress from the South Eugene Island field to relate a slipping interface to an amount of excess pore pressure in a fault zone.
UR: http://www.mines.edu/~rsnieder/thesis_Haney.pdf
DE: 3210 Modeling
DE: 5104 Fracture and flow
DE: 7203 Body wave propagation
DE: 8045 Role of fluids
DE: 8105 Continental margins and sedimentary basins
SC: Seismology [S]
MN: 2005 Joint Assembly