A study on the relationship between rock microstructure and wave disperson in carbonates and sandstones
* Presenting author
Rock anelasticity, i.e. acoustic wave velocity dispersion and attenuation, is related to porosity, texture and pore fluids. The relation is important to provide a basis for further rock physics studies and field applications of seismic exploration. In this work, ultrasonic compressional and shear wave velocities are measured in full-water and full-gas saturated tight carbonates, sandstones and volcanic rocks. By adding experimental data from the literature, we evaluate the compressional wave velocity dispersion as a function of porosity for all these lithologies (296 samples). It shows that the dispersion peaks at approximately 15 % porosity for each lithology, which we consider as a characteristic porosity, indicating that wave dispersion increases with porosity in the low porosity range, but decreases in the high porosity range. The poroelasticity theory is used to model the compressional wave dispersion. Results reveal that the microcrack radius and porosity have peaks at moderate porosities (15-19 %) for the three lithologies. The characteristics may be related to the diagenesis process and thus to microstructure of different lithologies. The new findings here reflect the intrinsic natures of shallow earth rocks, which will contribute to better understandings on earth rocks for researchers of rock physics and exploration geophysics areas.