Amplitude Partitioning And Elastic Wave Conversions In a Western Canada Offset VSP

A case study is presented of an offset vertical seismic profile conducted in northwest Alberta on a Precambrian test well. Despite pre-acquisition modeling, severe problems were encountered in retrieving useable signal from an offset source of around 1100m. The raw data were badly contaminated with mode conversions so that primary, upgoing energy from the 1800m zone of interest was ostensibly eliminated. A second phase of modeling was entered upon to explain the observed conversion patterns in the data. This process was iterative one involving modeling of the raypath geometries, P-wave and S-wave velocity layering about the borehole and the vertical components of non-normal incidence reflection and transmission coefficients.