Title: HTEM data improve 3D modelling of aquifers in Paris Basin, France,
Abstract: In Paris Basin, we evaluate how HTEM data complement the usual borehole,
geological and deep seismic data used for modelling aquifer geometries. With
these traditional data, depths between ca. 50 to 300m are often relatively
ill-constrained, as most boreholes lie within the first tens of meters of the
underground and petroleum seismic is blind shallower than ca. 300m. We have
fully reprocessed and re-inverted 540km of flight lines of a SkyTEM survey of
2009, acquired on a 40x12km zone with 400m line spacing. The resistivity model
is first "calibrated" with respect to ca. 50 boreholes available on the study
area. Overall, the correlation between EM resistivity models and the
hydrogeological horizons clearly shows that the geological units in which the
aquifers are developed almost systematically correspond to relative increase of
resistivity, whatever the "background" resistivity environment and the
lithology of the aquifer. In 3D Geomodeller software, this allows interpreting
11 aquifer/aquitar layers along the flight lines and then jointly interpolating
them in 3D along with the borehole data. The resulting model displays 3D
aquifer geometries consistent with the SIGES "reference" regional
hydrogeological model and improves it in between the boreholes and on the
50-300m depth range.