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

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