	SSP 1994 project summary:

[EPCC home] [SSP home] [2001 projects] [2000 projects] [1999 projects] [1998 projects] [1997 projects] [1996 projects] [1995 projects] [1994 projects] [1993 projects]

Modelling of Near-Field Properties of Seismic Wave in an Anisotropic Medium

In seismic monitoring of hydrocarbon reservoirs, the process of excitation, propagation and recording of important three-component seismic data is far from satisfactory. In a heterogeneous medium, many effects exist which cannot be directly assigned to either the source, medium or receiver. Further analysis is requried to help make this distinction clearer, so that the target zone may be resolved with confidence. The computation of complete body wave radiation from a seismic source in a homogeneous isotropic medium (2 elastic constants) does not pose anyu special probelms because the analytic form of Green's function exists for such a medium. However, no anlaytic solutions are as yet available for the case of a general anisotropic medium (21 elastic constants defining the microscale heterogeneity) The anisotropic case is particularly important as it provides a way of simulating heterogeneities and fractures around the source region. Fortunately, computations for the anisotropic medium can be achieved numerically. A 2d finite difference method based upon the elastodynamic equation of motion has been developed to study this problem.

The current simulation uses a finite different scheme which cannot compute displacements further than several wavelengths from the source due to inherent limitations of the hardware - principally time but also space. This prevents us from examining the impact of the near-field terms on tha actual recorded far-field radiation. In addition, there is no satisfactory way of simultaneously visualizing the results - directionally dependent wave properties of polarization, slowness and amplitude. This is required for a more thorough analysis of this effect.

The project involves the adaptation of the current finite difference code to run on a parallel machine. This will then be run and tested for different VSP (vertical seismic profile) geometries. Finally it is hoped that detailed visualization of polarization properties and slowness surfaces for seismic waves generated by a source embedded in an unbounded isotropic anisotropic medium will then be possible.

Sergio Damas Arroyo worked on this project.

Compressed PostScript of Sergio's final report is available here (489867 bytes) .

Webpage maintained by mario@epcc.ed.ac.uk