Stress Relaxing Simulation on Digital Rock: Characterize Attenuation Due To Wave-Induced Fluid Flow and Scattering

Digital rock physics (DRP) is essential to understand the wave elastic and attenuation characteristics of complex porous rocks, offering insights into interpreting seismic and sonic logging data. Most of the existing DRP technology can only simulate wave-induced fluid flow (WIFF) or scattering effects separately in a relatively narrow or single-frequency band. To incorporate both the effects of WIFF and elastic scattering simultaneously, we develop a stress relaxing simulation (SRS) technique on digital rocks to characterize the P wave dispersion and attenuation signatures in a broad frequency band. We propose to use the combined methodology of curve resampling and wavelet-packet denoising to suppress the high-frequency noise of the stress relaxation curve. For a digital rock containing pore-crack elements, we demonstrate that SRS is capable of characterizing the attenuation due to squirt flow and scattering as well as their interactions. The simulation results of wave dispersion and attenuation using SRS are overall consistent with other well-developed DRP technology of transmitted wave simulation (high-frequency band), forced oscillating simulation (intermediate-frequency band), and static simulation (low-frequency band), suggesting the reliability and robustness of the developed methodology. We also apply the SRS on a realistic 2D digital rock of porous sandstone. It is found that the attenuation due to elastic scattering of the microscopic heterogeneities is significantly higher than that caused by squirt flow, which might be caused by the lack of pore connectivity impeding the fluid exchange at the microscopic scale due to the limitation of 2D digital porous rocks.