Estimation of elastic wave properties of tight sandstones using a reformulated digital rock physics method and ultrasonic experiments

SUMMARY: Tight sandstone reservoirs, as a sort of widely distributed unconventional hydrocarbon resource, are characterized by complex microstructural features that give rise to intricate elastic wave responses. In this study, we estimate the wave properties of tight sandstones using a reformulated digital rock physics method. Nine tight sandstone cores from the Sichuan and Ordos Basins in China are selected for X-ray diffraction and ultrasonic measurements under varying pressures and fluid saturations. Variations in elastic wave velocities with respect to effective pressure are analysed for both gas and water saturation. Computed tomography (CT) scans at two resolutions are conducted to reconstruct multiphase digital rocks and investigate the effects of mineral boundaries (MB). Numerical simulations using the finite element and finite difference methods are then performed and compared with the ultrasonic data. The results show that the simulations can effectively estimate elastic properties when accounting for the effects of MB. Furthermore, the resolution of CT scans determines the scale of microstructures captured, which in turn dictates the pressure range over which the numerical simulations produce valid results. The findings indicate that the wave responses derived from these simulations are intrinsically linked to the scan resolution