Coda and Intrinsic Attenuations From Ultrasonic Measurements in Tight Siltstones

Abstract

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 method • Ultrasonic P wave coda attenuation in oil-water partially saturated siltstones is stronger than that at the full saturations • Coda and intrinsic attenuations depend on permeability, grain size, and skewness but generally do not depend on mineral content

Experimental Study on Petrophysical Properties as a Tool to Identify Pore Fluids in Tight-Rock Reservoirs

“…Siltstones were measured at a confining pressure of 50 MPa and a pore pressure of 25 MPa, whereas dolomites at 80 and 10 MPa, respectively. The adopted saturation method is described in the studies by Ba et al (2017) and Ma and Ba (2020). The partially gas-water and oil-water saturation tests were performed on the dolomites, but we conducted these tests only in five siltstones, and we set full saturation in others (gas, water, and oil, respectively).…”

“…P-and Swave attenuation were estimated by using one wave period with the centroid-frequency shift and spectral-ratio methods (Toksöz et al, 1979;Quan and Harris, 1997). The detailed measuring procedures and error analysis are given in the study by Ma and Ba (2020).…”

Temperature Effect on the Velocity‐Porosity Relationship in Rocks

“…(2009) and Ma et al. (2020). Ultrasonic measurements were performed with the central frequency of 1 MHz.…”

“…To measure the wave velocity, we use the ultrasonic wave pulse method described in Guo et al (2009) and Ma et al (2020). Ultrasonic measurements were performed with the central frequency of 1 MHz.…”

A stable implementation measure of multi-transmitting formula in the numerical simulation of wave motion

“…For the numerical simulations of near-field wave motions and the response of geological structures, the control equations of different media should be determined to obtain the reliable wave propagation characteristics [1][2][3][4][5]. Moreover, we need to truncate models of media in a finite-computational domain by introducing artificial boundaries.…”