A laboratory approach for the calibration of seismic data in the western part of the Swiss Molasse Basin: the case history of well Humilly-2 (France) in the Geneva area

Abstract A collection of 81 plugs were obtained from the Humilly-2 borehole (France), that reached the Permo-Carboniferous sediments at a depth of 3051 m. Experimental measurements of physical parameters and mineralogical analysis were performed to explore the links between sedimentary facies and seismic characteristics and provide a key tool in the interpretation of seismic field data in terms of geological formations. The plugs, cylinders of 22.5 mm in diameter and $\sim$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mo∼</mml:mo> </mml:math> 30 mm in length were collected parallel and perpendicular to the bedding in order to explore their anisotropy. Ultrasound wave propagation was measured at increasing confining pressure conditions up to 260 MPa, a pressure where all micro-fractures are considered closed. The derivatives of velocities with pressure were established, allowing the simulation of lithological transitions at in-situ conditions. At room conditions, measured grain densities (kg/m 3 ) range from 2630 to 2948 and velocities vary from 4339 to 6771 and 2460 to 3975 ${\text {m/s}}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mtextm/s</mml:mtext> </mml:math> for P- and S-waves propagation modes, respectively. The largest seismic-reflections coefficients were calculated for the interface between the evaporitic facies of the Keuper (Lettenkohle) and the underlying Muschelkalk carbonates ( R $_{\text {c}}=$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:msub mml:mrow/ mml:mtextc</mml:mtext> </mml:msub> mml:mo=</mml:mo> </mml:mrow> </mml:math> 0.3). The effective porosity has the range of 0.23% to 16.65%, while the maximum fluid permeability $\left( \text {m}^{\text {2}}\right)$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mfenced mml:msup mml:mtextm</mml:mtext> mml:mtext2</mml:mtext> </mml:msup> </mml:mfenced> </mml:math> is 9.1 $\times \text {10}^{-{\text {16}}}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> mml:mrow mml:mo×</mml:mo> mml:msup mml:mtext10</mml:mtext> mml:mrow mml:mo-</mml:mo> mml:mtext16</mml:mtext> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> . A positive correlation between porosity and ultrasound velocity has been observed for P- and S-waves. The link between velocities and modal content of quartz, dolomite, calcite, and micas has been explored. This paper presents a unique set of seismic parameters potentially useful for the calibration of seismic data in the Geneva Molasse Basin.