Velocity‐porosity‐clay content systematics of poorly consolidated sandstones

Abstract

Compressional velocities have been measured as a function of confining pressure for 14 West Delta Block (Louisiana) sandstone cores. The dry velocity data for these poorly consolidated sandstones at 10 MPa confining pressure plot on a linear velocity‐density trend with well‐consolidated sandstones but not loose sands. The dry velocity data also show linear trends of decreasing velocity with increasing porosity along contours of constant clay content similar to those obtained at 40 MPa by Tosaya and Nur (1982) for saturated sandstones. The spacing between clay contours indicates that a large portion of the velocity variation with clay content is due to microporosity, which is not included in point counting, within the clays. The slope of the velocity‐porosity trends indicates that cementation increases with decreasing porosity.

Re-evaluation of temperature at the updip limit of locked portion of Nankai megasplay inferred from IODP Site C0002 temperature observatory

“…Han et al (1986) measured Vp for sedimentary rocks and showed a linear relationship between Vp, porosity, and clay content. Taking the Vp of approximately 4 km/s obtained from seismic surveys (e.g., Nakanishi et al 2008), the porosity was estimated at approximately 10% for 50% clay (Han et al 1986) to approximately 0% for 70% clay (Kowallis et al 1984). Although we did not determine the clay abundance below Site C0002, these estimates are in general agreement with resistivity-derived values.…”

Review article "Remarks on factors influencing shear wave velocities and their role in evaluating susceptibilities to earthquake-triggered slope instability: case study for the Campania area (Italy)"

“…Nevertheless, this effect was found to be negligible in rocks with identical porosity, lithology and similar clay content. We add that, for poorly consolidated sandstones at 10 MPa confining pressure, Kowallis et al (1984) showed dry velocity data with linear trends of decreasing velocity with increasing porosity similar to those obtained by Tosaya and Nur (1982) for saturated sandstones at 40 MPa. A correlation between compressional and shear wave velocities can be obtained from the equations shown in Table 2b proposed by Castagna et al (1985) and Han et al (1986).…”

“…Those clay particles create a micro-porosity made of pores smaller than 1 µm, which increases the porosity of the medium and greatly influences the velocity of seismic waves, decreasing it (e.g. Kowallis et al, 1984;Tosaya and Nur, 1982;Han et al, 1986, Goldberg andGurevich, 1998;Klimentos and McCann, 1990). …”

Contact micromechanics in granular media with clay

“…The first studies showed that scatter in the velocity-porosity relationships for consolidated rocks could be partially explained by clay content (DeMartini et. al., 1976;Tosaya and N u , 1982;Kowallis et. al., 1984).…”