The effect of viscoelasticity and microplasticity on the P- wave attenuation in dry and water-saturated sandstone: An experimental study

Abstract

Seismic studies use a viscoelastic model of a standard inelastic body that does not take into account the effect of microplasticity of the rocks. The modern approach introduces the new components, which indeed improves the efficiency of the seismic methods. The aim of this study is to determine the combined effect of viscoelasticity and microplasticity on the longitudinal wave's attenuation. The high-resolution measurements performed on dry and water-saturated sandstone by a pulse frequency of 1 MHz within the strain ranges of ~ (0.3–2.0) × 10-6 under 10 MPa confining pressure. Within the range of 0.5–2.5 MHz at both states of the dry and water-saturated sample, the frequency dependence of P- wave attenuation Qp−1(f) forms a peak due to the viscoelasticity. Microplasticity effect manifests as a non-linear dependence of the wave attenuation Qp−1(ε) on the strain amplitude. By increasing the strain amplitude the attenuation peak in the saturated sandstone shifts towards the higher frequencies and Qp−1- values. The indicators of microplastic deformation on the wave profile are the stress plateau and the stress drop feature. Within the range of 1.5–2.5 MHz frequencies the microplasticity is increased on the attenuation spectrum. The significant difference between dry and water-saturated sandstone can be observed as a change in peak and value of the attenuation. Considering microplasticity in the models and introducing the number of stress plateaus into a wave profile shows a significant effect of this factor on the wave attenuation. Unconventional behavior of the wave attenuation is explained by a joint action of viscoelastic and micro-plastic mechanism. The results of this study can contribute in improvement of the methods of geological interpretation of the seismic and acoustic data.