Mapping Buried Aquifers with HTEM in the Fort McMurray, Alberta Region

Abstract

Heliborne time-domain electromagnetic systems (HTEM) have proven to be effective tools in mapping sub-surface resistivity. As these systems are able to measure increasingly earlier time channels after the waveform's turn-off, they improve their ability to resolve resistivity contrasts in near-surface geology. This is demonstrated with the VTEM system over the Aspen property, near Fort McMurray, Alberta. This area provides a useful setting in mapping near-surface resistivity variations, specifically the location and geometry of the Pemmican Valley aquifer. This begins with the a Tau constant analysis of the earliest time channels of the VTEM decay curve that laterally mapped the Pemmican Valley aquifer and the existence of a shallower, previously unmapped, east-west trending aquifer. This is confirmed through 1D inversions of the dataset. The 1D inversion models accurately resolve the main near-surface geo-electrical units within the Aspen property when compared to resistivity well logs and a ground DC resistivity survey. Analysis of the stitched 1D inversion section maps provides useful resistivity maps that reflect the geological model.