On the low-frequency elastic response of Pierre Shale during temperature cycles

Abstract

Summary The impact of temperature on elastic rock properties is less-studied and thus less-understood than that of pressure and stress. Thermal effects on dispersion are experimentally observed herein from seismic to ultrasonic frequencies: Young’s moduli and Poisson’s ratios plus P- and S-wave velocities are determined by forced-oscillation (FO) from 1 to 144 Hz and by pulse-transmission (PT) at 500 kHz. Despite being the dominant sedimentary rock type, shales receive less experimental attention than sandstones and carbonates. To our knowledge, no other FO studies on shale at above ambient temperatures exist. Temperature fluctuations are enforced by two temperature cycles from 20 via 40 to 60○C and vice versa. Measured rock properties are initially irreversible but become reversible with increasing number of heating and cooling segments. Rock property-sensitivity to temperature is likewise reduced. It is revealed that dispersion shifts towards higher frequencies with increasing temperature (reversible if decreased), Young’s moduli and P-wave velocity moduli and P-wave velocity maxima occur at 40○C for frequencies below 56 Hz, and S-wave velocities remain unchanged with temperature (if the first heating segment is neglected) at seismic frequencies. In comparison, ultrasonic P- and S-wave velocities are found to decrease with increasing temperatures. Behavioural differences between seismic and ultrasonic properties are attributed to decreasing fluid viscosity with temperature. We hypothesize that our ultrasonic recordings coincide with the transition-phase separating the low- and high-frequency regimes while our seismic recordings are within the low-frequency regime.

Anisotropic 4D seismic response inferred from ultrasonic laboratory measurements: A direct comparison with the isotropic response

“…Although these assumptions seem to be reasonable, the best way is to remove them by conducting seismic frequency measurements on saturated rocks with controlled pore pressure. The forced‐oscillation technique (e.g., Rørheim et al., 2022) is commonly used for this purpose; however, it is non‐standard for most laboratories. Other potential issues include the impact of heterogeneity (He & Wang, 2020), which is difficult to be accounted for by any laboratory measurements on core plugs.…”

On Frequency-Dependent Rock Experiments: A Comparative Review

“…Batzle et al [33] identified nodes and antinodes to extend this upper boundary by distributing the measurements accordingly. Since dispersion is a fluid-dependent phenomenon, viscosity-manipulation either by fluids such as glycerine [33,103,122,129,131,145,[168][169][170]218] or temperature [33,50,107,190] may shift the transition from unprobed to probed frequencies due to altered fluid mobility. Viscosity-manipulation by temperature [271] is explored at high but unexplored at low temperatures for FO.…”

“…Neither PT measured V P0 nor V S0 significantly changed perhaps due to Draupne's low calcite content. Rørheim et al [190] combined FO and PT at elevated temperatures for 0 and 90 • Pierre specimens: FO measured E V and E H dispersion shifted towards higher frequencies while FO converted and PT measured V P0 , V P90 , V S0 , and V S90 oppositely decreased and increased with temperature. Two simple frequency-dependent bound water models were also proposed.…”

Calibración de modelos de física de rocas poroelásticos en shales orgánicas argentinas y aplicaciones

“…Un estudio exhaustivo de las propiedades elásticas de las shales para un rango de bajas frecuencias fue llevado a cabo por Szewczyk [2017]; Szewczyk et al [2018a, b]; Lozovyi y Bauer [2019]; Mikhaltsevitch et al [2021]; Rorheim et al [2022]. Los autores ensayan muestras de shales por medio de la técnica de oscilaciones forzadas utilizando un dispositivo propio que permite el control del esfuerzo deviatórico, presión poral, obtención de ultrasonido y mediciones estáticas [Szewczyk et al, 2016].…”