Shear‐wave velocity anisotropy in sedimentary rocks: A laboratory study

Abstract

A systematic laboratory study of shear-wave velocity anisotropy in sedimentary rocks has been carried out as a function of both hydrostatic and uniaxial stress. The presence of shear-wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver. The magnitude of the observed velocity anisotropy is dependent upon the magnitude and nature of the applied stress and the lithology of the rock sample. Shales exhibit significant velocity anisotropy independent of both uniaxial and hydrostatic stress, which suggests the presence of preferentially aligned minerals. Sandstones also exhibit significant velocity anisotropy, but the anisotropy is strongly dependent upon the stress. Hydrostatic stress was found to diminish the velocity anisotropy and uniaxial stress was found to enhance it. This implies the presence of preferentially oriented cracks. Limestones exhibit weak velocity anisotropy. These laboratory observations may be helpful in in situ identification of lithology.

Texture development in naturally compacted and experimentally deformed silty clay sediments from the Nankai Trench and Forearc, Japan

“…Bennett et al, 1981;Fawad et al, 2010;Jones, 1994;Rai and Hanson, 1988;Voltolini et al, 2009). Microfabrics, especially preferred alignment of minerals, control this anisotropy, which in turn has implications for seismic and hydrogeological modeling (e.g.…”

“…Microfabrics, especially preferred alignment of minerals, control this anisotropy, which in turn has implications for seismic and hydrogeological modeling (e.g. Johansen et al, 2004;Rai and Hanson, 1988;Voltolini et al, 2009). Fabric genesis also changes the frictional behavior of clay-bearing sediments (e.g.…”

Experimental mechanical compaction of clay mineral aggregates—Changes in physical properties of mudstones during burial

“…Successful imaging of the reservoir intervals depends on correct parameters describing the wave propagation through the overlying shaley sequences. The existing shale velocity database suggests that seismic propagation through shales is a function of the intrinsic anisotropy of the clay minerals (Banik, 1984;Hornby et al, 1994;Vernik and Liu, 1997), compliance between clay minerals (Sayers, 1994) and their microstructure (Rai and Hanson, 1988;Vernik and Nur, 1992). Velocities in clay-matrix supported silisiclastic sediments are also sensitive to the chemistry of the fluids saturating their pore spaces (King, 1966;Liu et al, 1994) and the stress state (Jones and Wang, 1981;Johnston, 1987) over the whole porosity range found in mudstones and shales.…”

Velocity anisotropy of Upper Jurassic organic-rich shales, Norwegian Continental Shelf

“…Beside the nonlinear trend of velocity-effective stress trends at low effective stress levels, some authors show less sensitivity of velocity to effective stress by observing a linear relationship between these two parameters even at low effective stress levels (Vernik and Nur, 1992;Vernik and Landis, 1996;Dewhurst and Siggins, 2006;Sondergeld and Rai, 2011). Rai and Hanson (1988) document a small pressure dependence of the velocity values measured in fresh and well-preserved shale cores. Similar behavior is observed for the measured velocities in the Draupne shale which is collected from a relatively fresh core (acquired in 2013).…”