Shallow VSP survey using a small vibrator source

Soo-Kyung Miong, Joe Wong, Eric V. Gallant, Robert R. Stewart, Kevin W. Hall

A shallow VSP survey was conducted in the Rothney Test Well using the U of C EnviroVibe as a source and a downhole clamping 3-C geophone in the well. The receiver was placed at depths ranging from 5 m to 90 m at half-metre intervals. Two VSPs were recorded with the vibrator located 15 m and 30 m south of the well head. The three-component data were subjected to wavefield separation and vector rotation to separate P and S waves. Down-doing wavefields, as well as up-going and down-going tube waves, were removed to isolate the P-wave reflections. The residual up-going P-wave reflections were mapped using an approximate VSP/CDP procedure. The reflectivity maps showed good correlation with resistivity, gamma ray, and sonic velocity logs in the well. The experiment confirmed the belief that the EnviroVibe vibrator, when used as a source in near-surface VSP surveys, produces enough high-frequency energy to be effective for imaging relatively thin stratigraphy in the upper 100 m.