Slopes of an airborne electromagnetic resistivity model interpolated jointly with borehole data for 3D geological modelling

Abstract

International audienceWe investigate a novel way to introduce resistivity models deriving from airborne electromagnetic surveys into regional geological modelling. Standard geometrical geological modelling can be strengthened using geophysical data. Here, we propose to extract information contained in a resistivity model in the form of local slopes that constrain the modelling of geological interfaces. The proposed method is illustrated on an airborne electromagnetic survey conducted in the region of Courtenay in France. First, a resistivity contrast corresponding to the clay/chalk interface was interpreted confronting the electromagnetic soundings to boreholes. Slopes were then sampled on this geophysical model and jointly interpolated with the clay/chalk interface documented in boreholes using an implicit 3D potential-field method. In order to evaluate this new joint geophysical–geological model, its accuracy was compared with that of both pure geological and pure geophysical models for various borehole configurations. The proposed joint modelling yields the most accurate clay/chalk interface whatever the number and location of boreholes taken into account for modelling and validation. Compared with standard geological modelling, the approach introduces in between boreholes geometrical information derived from geophysical results. Compared with conventional resistivity interpretation of the geophysical model, it reduces drift effects and honours the boreholes. The method therefore improves what is commonly obtained with geological or geophysical data separately, making it very attractive for robust 3D geological modelling of the subsurface

Hydrogeophysical Characterization in a Volcanic Context From Local to Regional Scales Combining Airborne Electromagnetism and Magnetism

“…While well data often constrain resistivity models (e.g., Ball, Davis, et al., 2020; Reninger et al., 2016), no near‐surface drill holes exist and the great spatial variability of lithology and groundwater processes on volcanoes would not be perceived from scarce drill holes. In order to take such complexity into account, we experiment with an approach based on the definition of geo‐electrical features.…”

Agglomerative hierarchical clustering of airborne electromagnetic data for multi-scale geological studies

“…Alternatively, coupled with borehole data, 3D geological structures can be highlighted, located and characterized (Auken et al, 2008;Christensen et al, 2015) but this cannot be automated for large datasets. Alternatively, resistivity contrasts linked to specific geological contacts can be represented as isoresistivity depth maps or interpolated resistivity slope maps (Reninger et al, 2016). This remains quite specific as both approaches require simple geological contexts to be reliable.…”