Variation in dynamic elastic shear modulus of sandstone upon fluid saturation and substitution

Abstract

Experimental acoustic measurements on sandstone rocks at both sonic and ultrasonic frequencies show that fluid saturation can cause a noticeable change in both the dynamic bulk and shear elastic moduli of sandstones. We observed that the change in dynamic shear modulus upon fluid saturation is highly dependent on the type of saturant, its viscosity, rock microstructure, and applied pressures. Frequency dispersion has some influence on dynamic elastic moduli too, but its effect is limited to the ultrasonic frequency ranges and above. We propose that viscous coupling, reduction in free surface energy, and, to a limited extent, frequency dispersion due to both local and global flow are the main mechanisms responsible for the change in dynamic shear elastic modulus upon fluid saturation and substitution, and we quantify influences.

Effects of desiccation on the elastic wave velocities of clay-rocks

“…The results presented above show two remarkable features, which were not observed in other sedimentary formations (e.g., sandstones and limestones) subjected to low mechanical pressures and to saturation paths involving the same narrow range of water content(e.g., [21][22][23]): when the degree of saturation decreases, and lies in the range 0-50%. In the case of samples EST05-624 and EST05-687, V p increases with two distinct trends, depending on the two main textural directions in which it is measured, whereas V s increases significantly, by as much as 10%.…”

“…Firstly, this phenomenon is clearly associated with the clay matrix. In particular, it was not observed in ''clean'' sandstones with the same range of water content at low mechanical pressures (e.g., [21][22][23]), whereas it seems to have been enhanced in sample EST05-687, which had a higher clay content (see Table 1 and Fig. 3d).…”

Rock physics template from laboratory data for carbonates

“…They also mentioned that the pore shape is not easy to quantify but is one important rock property for the elastic properties. Other researchers like for example Khazanehdari and Sothcott (2003), Baechle et al (2009), Adam et al (2006 or Pimienta et al (2014) add this. They all summarized that the change of dynamic shear modulus with saturation, especially for carbonates is a result of rock-fluid interaction and the underlying rock microstructure.…”

Frequency-dependent wave velocities in sediments and sedimentary rocks: Laboratory measurements and evidences

“…In the above example with synthetic unconsolidated sand (see Figure 1), ultrasonic velocities of dry and water-saturated samples could well be described by assuming the matrix stiffness is not affected by the water. For natural rocks, this assumption is often not valid; interaction with water often results in significant rock softening (Khazanehdari and Sothcott, 2003;Adam et al, 2006). The underlying mechanisms are not fully understood yet.…”