Processing and inversion of SkyTEM data. Peace River North-Western Area. Report # 2018-06 for Geoscience BC.

This study is part of the Peace Project. The Peace Project is a collaborative effort involving Geoscience BC, the Ministry of Forests, Lands and Natural Resource Operations, the Ministry of Environment, the BC Oil and Gas Commission, the Ministry of Natural Gas Development, BC Oil and Gas Research and Innovation Society (BC OGRIS), Progress Energy Canada Ltd., and ConocoPhillips Canada, with additional support from the Peace River Regional District and the Canadian Association of Petroleum Producers. The authors of this report acknowledge the in-kind and funding support these partners have made to this study, through their contributions to the Peace Project.

This report covers the processing, inversion and (hydro)geological interpretation of the SkyTEM data over a portion of the entire SkyTEM survey acquired in the Peace Project. More specifically, it contains results covering the Peace River “North-Western” area. The AEM and navigation data were first re-processed, starting from raw data, adopting state of the art methodologies aimed at reducing artefacts in the data, and therefore in the derived models. They were then inverted to 3D resistivity models using both Laterally and Spatially Constrained Inversions. Preliminary inversion results were analyzed against ancillary information and provided feedback for data post-processing and final inversions. An extensive set of high-resolution maps of electrical resistivity slices (1:50.000 scale) at different elevations and depths has been provided. The resulting 3D model was then correlated to known geological information to produce a hydrogeological model.

From a geophysical standpoint, the main results of this study include: spatial variability of the resistivity models reflecting potential changes in geology, both near surface and at depth; excellent fit between measured and modelled data, independent of geology or flight lines; seamless models, despite the data were acquired under varying conditions and over a period of several weeks; depth of investigation exceeding, in places, 300 m; effective removal of potential canopy effects; good correlation with depth to bedrock inferred from boreholes.

The derived qualitative geological interpretation highlights: differentiation of different facies within the glacial cover (e.g., resistive glaciofluvial deposits versus the more conductive glaciolacustrine deposits); confirmation of several near surface resistive features associated with paleovalleys and/or areas of thick Quaternary cover identified by previous studies of borehole data; presence of other near surface resistive features that could be of hydrogeological relevance; clear conductive response of the shale bedrock formations (Sully and Buckinghorse); predominantly resistive response of the sandstone Dunvegan bedrock formation; inconsistent response of the predominantly sandstone Sikanni bedrock formation (variability of the sandstone responses might be due to inhomogeneous grain size or water quality); presence of resistive units, in places, at the bottom of the Buckinghorse formation; presence of deep (in excess of 200 m) features with geological continuity, extending over significant distances.

The detailed hydrogeological interpretation and 3D modelling is mainly focused on buried palaeovalleys, which represent the most promising potential for sustainable groundwater production in the area. Some of those valleys were likely formed as tunnel valleys containing enclosed depressions that may be filled with coarse-grained material. At least two generations of valleys seem to be present separated by a widespread glaciolacustrine unit and fluvial sediments. These units, together with the older bedrock units, are included in a 3D model. Although only constructed for a small portion of the entire survey area, this model can potentially be used for planning future groundwater modelling.