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The Impact of Strain Amplitude on Young's Modulus in Water-Saturated Sandstone

Abstract

Strain amplitude, frequency, stress conditions, and fluid saturation influence the stiffness response of rocks. In order to quantify the effect of frequency and strain amplitude, we performed low-frequency measurements on fully saturated Bentheimer sandstone samples to measure the dynamic stiffness at seismic frequencies (0.5 – 143 Hz) with strain amplitudes ranging from 10−7 to 10−5 . In order to quantify the effect of pressure, we increased the effective stress subsequently. The results show that Young’s modulus decreases with increasing strain amplitude even in the seismic-frequency range. The applied wave-stress signal contains the first harmonic at the central frequency, but the measured wave strain rate spectrum contains higher-order harmonics indicating hysteresis in the stress-strain response. The increased signal at higher-order harmonics is only captured for higher strain amplitudes. The general trend shows a decreasing signal with increasing order of harmonics. Remarkable is that the 3rd harmonic indicates a stronger signal than the 2nd harmonic and the 5th harmonic a stronger signal than the 4th. Understanding non-linearities and non-elastic mechanisms and their dependency on the strain amplitude for saturated samples are fundamental for the link between dynamic and static properties of reservoir rocks.

Category

Academic chapter

Language

English

Author(s)

Affiliation

  • SINTEF Industry / Applied Geoscience
  • Norwegian University of Science and Technology

Year

2022

Publisher

American Rock Mechanics Association (ARMA)

Book

56th U.S. Rock Mechanics/Geomechanics Symposium

ISBN

9780979497575

View this publication at Norwegian Research Information Repository