Resolution Issues with Regard to Seismic Elastic Lithologic Modeling

Keith Wrolstad

The resolution of thin layers in the earth's subsurface has been investigated using non-normal incidence, plane-layer elastic synthetic modeling. Single-layer and multilayer models are computed with varying layer thicknesses having elastic constants appropriate for water- and hydrocarbon-saturated sands, shales, and carbonates. Pre-stack and post-stack attributes of the synthetic traces are computed to investigate reflection and transmission propagation effects. Tuning and multiple interference must be considered in the interpretation of amplitude versus offset (AVO). Converted shear events must be identified, as they always have increasing AVO. Even though the top and bottom of a thin-layer reflector cannot be resolved, the compressional primary elastic reflection coeffi ients are still observable if corrections are made for tuning and multiple interference. Strong angle or offset dependent attenuation occurs upon transmission of elastic waves through low Poisson's ratio, gas-saturated sands. Amplitude and phase attributes of partial stack traces are very useful for observing very subtle changes in wave shape caused by these propagation effects.

AAPG Search and Discovery Article #91035©1988 AAPG-SEPM-SEG Pacific Sections and SPWLA Annual Convention, Santa Barbara, California, 17-19 April 1988.