Spatial resolution and amplitude studies in anisotropic seismic reflection: a physical modelling study

Abstract

Physical seismic modelling experiments have been conducted to analyse the effects of anisotropy on spatial resolution and amplitudes of reflectors of varying sizes using phenolite and plexiglass materials which simulate anisotropic and isotropic media respectively. Cylindrical holes of progressively increasing sizes were drilled into the bottom centres of both models. The hole sizes were varied from 0.19 to 1.33 and from 0.35 to 2.10 times the expected Fresnel-zone diameters in phenolite and plexiglass respectively. These holes, while serving as reflectors, also simulate a range of geological features, e.g. pinnacle reefs, intrusions, seals, and pipes, etc. The spatial extents of the reflector boundaries are estimated by marking the half-amplitude points of the horizontal reflector events with respect to the amplitude at the centre of the reflectors. The degree of horizontal resolution is determined by comparing the seismically estimated reflector dimension with the true spatial dimension of the reflector. The resolving potentials of pressure and shear body waves in anisotropic and isotropic media were compared using the collected data. Results obtained so far indicate that the presence of anisotropy would significantly affect the spatial resolving powers of body waves. Hence spatial resolution in an anisotropic medium would be quite different from that determined for the same medium if it is assumed isotropic. Consequently, the spatial resolution of seismic events from the base of thick shale sediments is most likely to be affected.