Role of Saturation on Elastic Dispersion and Attenuation of Tight Rocks: An Experimental Study

Abstract

Using the forced-oscillation method, we measure the dispersion of Young's modulus, extensional attenuation, and Poisson's ratio of tight sandstone and carbonate samples at seismic frequencies (1-1000 Hz) under a constant confining pressure of 20 MPa and for a water saturation varying between 0% and 100%. The experimental data suggest that the dispersion of Young's modulus and attenuation of tight rocks is significant in a broad frequency band spanning over 1-1000 Hz. A comparison with the high-porosity and high-permeability sample data shows a contrasting dispersion and attenuation characteristics. For the tight sandstone, Young's modulus reaches a maximum dispersion of 16% at 60% water saturation and a 13% dispersion at 100% saturation. Attenuation is insignificant in dry condition and for water saturation ≤30%. In contrast with the peak attenuation occurring at very high water saturation (e.g., 80-100%) in partially saturated high-porosity rocks, peak attenuation of tight sandstone takes place at a water saturation of 60%. For the tight carbonate, the magnitude of dispersion (~3%) and attenuation are markedly lower for all saturation levels. In the explored frequency range (1-1000 Hz), Young's modulus increases monotonously, and no obvious attenuation peak is observed when saturation levels are greater than 10%. Using well-established theoretical models based on physical properties and microstructure of the tested rocks, we suggest that the observed attenuation characteristics are possibly attributed to the combined physical mechanism of microscopic (squirt) flow, mesoscopic flow in partially saturated rock, and shear dispersion due to viscous flow in grain contacts. Key Points:• Dispersion and attenuation of both tight sandstone and carbonate are distributed across frequency range of 1-1000 Hz • Extensional attenuation in tight sandstone is saturation dependent with a maximum at 60% saturation, which contrasts with that of porous sandstones • The coupled pore fabric and fluid distribution heterogeneity in tight rocks might cause complex dispersion and attenuation characteristics

Wave Propagation in Infinituple‐Porosity Media

“…The measured data can be found in Li et al. (2020), Batzle et al. (2006), and Zhou et al.…”

Analysis of the frequency dependence characteristics of wave attenuation and velocity dispersion using a poroelastic model with mesoscopic and microscopic heterogeneities

“…Ren et al ., 2009; Quintal et al ., 2011a; Zhao et al ., 2015, 2017; He et al ., 2018, 2020) and also using laboratory experiments (e.g. Batzle et al ., 2006; Bouzidi and Schmitt, 2006; Yin et al ., 2017; Li et al ., 2020a and 2020b).…”

Combined effects of permeability and fluid saturation on seismic wave dispersion and attenuation in partially-saturated sandstone

“…Porous rocks are normally saturated with multiphase fluids underground (Zhao et al, 2017;Li et al, 2020a). When seismic waves passing through such subsurface rocks, it is unavoidable to create dissipative and dispersive responses.…”

“…Consequently, efforts must be made to precisely measure the dispersion and attenuation at seismic frequency bands and under varying physical conditions. Due to the high requirement of precision and the complexity of laboratory measurements, there are limited teams capable of conducting low-frequency measurements so far (Spencer, 1981;Batzle et al, 2006;Tisato and Quintal, 2013;Pimienta et al, 2015Pimienta et al, , 2019Mikhaltsevitch et al, 2016;Li et al, 2020a). The most prospecting method in low-frequency measurements is the forced-oscillation technique, allowing measurements over a wide frequency range and under varying physical conditions.…”