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Swiss Journal of Geosciences
Fig. 8 | Swiss Journal of Geosciences

Fig. 8

From: 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

Fig. 8

Example of two cycles of pressurization–depressurization of compressional-waves (sample HU25X). The non-linear velocity/pressure correlation at low pressure (up to ca. 175 MPa) is due to the closure of cracks/pores. The linear velocity/pressure correlation is due to intrinsic compressibility elastic moduli of the mineral skeleton of the rock. The velocity measurements during the depressurization run (filled symbols) show larger values than those obtained during the pressurization runs (empty symbols). This effect (hysteresis) is interpreted as due to the only partial re-opening of fractures and microcracks that close during pressurization. The intrinsic velocity \(\textit{V}_{\text {p}}(\text {0})\) was calculated by the linear regression (red line) intersection of the high-pressure part of the second depressurization 2nd run back to the zero-confining pressure. These coefficients of the linear regression are corresponding to the pressure derivative of velocities. The fitting curve was calculated on the 2nd complete run using the Wepfer and Christensen (1991) equation

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