Coda and Intrinsic Attenuations From Ultrasonic Measurements in Tight Siltstones.

We have performed ultrasonic measurements on tight siltstone samples to obtain the P wave coda and intrinsic attenuations using a single isotropic scattering model and the spectral ratio method. The results indicate that attenuation is predominantly caused by scattering. Intrinsic attenuation increases with gas saturation and permeability and decreases with grain size, whereas coda attenuation is stronger under partial saturation conditions and increases with grain size. Porosity and mineral composition do not have significant effects on attenuation. The triple‐porosity and scattering models are used to simulate the intrinsic and scattering attenuations, respectively. The results show that the intrinsic attenuation is predominately caused by wave‐induced fluid flow between microcracks/micropores and intergranular pores. The model incorporating the scattering effects of microcracks underestimates the scattering loss in the coda, which may thus be better explained by heterogeneities in the clustering structure of grains. Key Points: Coda and intrinsic attenuations in siltstones are estimated with a single isotropic scattering model and the spectral ratio methodUltrasonic P wave coda attenuation in oil‐water partially saturated siltstones is stronger than that at the full saturationsCoda and intrinsic attenuations depend on permeability, grain size, and skewness but generally do not depend on mineral content [ABSTRACT FROM AUTHOR]