Acquisition and preliminary analysis of the Castle Mountain shallow VSP dataset
Joe Wong, Henry C. Bland, Kevin W. Hall, Robert R. Stewart
As part of the 2006 geophysics field school for the University of Calgary Department of Geology and Geophysics, a shallow VSP survey was conducted by students in two water wells at the Castle Mountain Ski Resort near Pincher Creek in southwestern Alberta. The wells were drilled in unconsolidated sand and gravel to total depths of about 37 and 42 meters, ending a meter or so into shale bedrock. A 7.3 kg sledge hammer source was used with a pressure-proofed clamping 3C geophone and an eight-element hydrophone array as the downhole sensors. A Geometrics R60 seismograph recorded data at various source offsets from the wellhead. Both P and S events were present on the data. Using picked arrival times and source-detector separations, apparent velocities were estimated to lie between 1100 m/sec to 2000m/sec for the P wave, and between 350m/sec to 400 m/sec for the S wave. A more accurate P-wave velocity versus depth profile around one of the wells was obtained by modelling the arrival times using a refracting boundaries ray-tracing program. Future processing of the data will attempt to identify reflections from the overburden/bedrock interface for VSP/CDP imaging.