Eric V. Gallant

Seismic physical modeling at the University of Calgary

The seismic physical modeling facility at the University of Calgary has existed since 1985. Recently, we upgraded it by replacing obsolete components with modern alternatives. We constructed a 3D positioning system based on high-precision linear electric motors, and coupled it to arrays of multiple transmitting and receiving piezoelectric transducers. We wrote customized software executing on the latest generation of desktop computers for controlling transducer movements, selecting and activating individual transducers, and acquiring and recording files of digital seismograms. The modernized facility enables us to collect scale-model seismic gathers at rates of thousands of traces per hour. We present examples of data from modeled 2D marine and land seismic surveys.

VSP survey in a shallow well using a small vibrator source

Summary A shallow VSP survey was conducted in the University of Calgary Test Well using an EnviroVibe vibrator source and a downhole clamping 3C geophone. The goal was to evaluate VSPs for imaging thin-bed stratigraphy in the nearsurface environment. Two offset VSPs were obtained with the vibrator located 15m and 30m south of the wellhead. The vertical component data were subjected to wavefield separation to remove down-going P and S waves, and laterarriving (low-velocity) up-going and down-going events. The residual up-going P-wave reflections were further processed and mapped using a simplified VSP/CDP procedure. Features on the resulting reflectivity maps corresponded closely to the near-surface stratigraphy of the Paskapoo formation close to the well as identified by sonic velocity, resistivity, and natural gamma-ray logs. The project confirmed that the EnviroVibe vibrator used in nearsurface VSP surveys produces enough high-frequency energy to be effective for imaging relatively thin lithological beds in the upper 100m.

3D ground‐penetrating radar over ice and permafrost

Ground penetrating radar (GPR) studies have been conducted at two sites (Devon Island, Nunavut and Bowness Park, Calgary) to study the character of ice, permafrost, and the shallow subsurface. We have used Sensors and Software Inc.’s NOGGIN 250 MHz system as well as the Pulse EKKO 4 system with 50, 100, and 200 MHz antennae. A 3D GPR survey was conducted over a frozen lagoon at Bowness Park in Calgary. Hyperbolic velocity analysis gave ice velocities of about 0.15 m/ns with velocities decreasing into the sediments to about 0.11 m/ns. We interpret the ice thickness to be about 0.4 m from the GPR, which is consistent with augur holes drilled through the ice. Channel sediments and stratigraphy beneath the ice are interpretable from the 3D radar reflectivity. Penetration of the 250 MHz data reached about 4 m at several locations in the area. On the Devon Island, we were surveying near or on the rim of the Haughton meteorite impact structure. A number of shallow excavations found the permafrost to be at a depth of 50-60 cm beneath a silty or brecciated layer. We found a strong reflection returned from the surface layer-topermafrost interface.