Vitesse des ondes ultrasonores, soniques et sismiques dans les argilites du tunnel de Tournemire. Effet de l’anisotropie et de la fracturation naturelle.
B. Zinszner, P. Meynier, J. Cabrera, P. Volant
Oil & Gas Science and Technology – Rev. IFP, Vol. 57 (2002) N°4, pp. 341-353
Abstract in english but full text in French.
Elastic wave velocities in dense shale were measured at three scales of investigation: ultrasonic (laboratory), sonic (log) and seismic (tomography), using IPSN research facilities in the Tournemire tunnel (Aveyron, France).Tournemire shale exhibits a high transverse isotropy and the sonic/seismic measurements were performed in both a naturally fractured area (tectonic, near a subvertical fault) and a nonfractured area. This allows an investigation of the impact of fractures on wave velocity.Among the conclusions of practical importance for applied geophysics, one can point out:- the high P wave velocity anisotropy measured on centimetric samples is quantitatively the same that measured at decametric scale using seimics tomography;- the tectonic fractures have a noticeable impact on P wave velocity. The P velocity is lower in the fractured area. Unfortunately, the S-wave velocity could be measured at ultrasonic frequency only.