The elastic properties and anisotropy of artificial compacted clay samples

Abstract

Clay minerals are a major component of hydrocarbon reservoir rocks, and are known to play important roles in physical and elastic properties of rocks. However, it is difficult to directly measure these properties of single-crystal clays due to their small particle size. Therefore, we construct three sets of artificial clay samples with different compaction stresses to investigate the effect of the compaction stress and clay mineralogy on their elastic properties and anisotropy. All the dry samples are measured by the pulse-transmission method. The results indicate that the compaction stress and clay mineralogy have significant influence on the physical and elastic properties of the clay samples. The microstructures of clay samples indicate that the clay platelets are aligned almost perpendicularly to the direction of compaction stress, and the ultrasonic velocity analysis validates the assumption of transverse isotropy of our clay samples. The velocities increase with the compaction stress, especially at low stress, which corresponds to the rapid porosity reduction at low stress levels. Velocity anisotropy parameters increase with increasing of compaction stress due to the increase of texture sharpness for clay minerals during the compaction process. The elastic moduli of the clay samples display a significant stress sensitivity and a strong directional dependence, with the Young’s moduli increasing and the Poisson’s ratios decreasing with the compaction stress. A simple theoretical template is used to quantify the orientation distribution functions (ODF) of clay platelets, and the Generalised Legendre coefficients of ODF increase with the increase of compaction stress, especially at low stress. Further, both the P- and S- wave anisotropy increase with the ODF coefficients W200 and W400, especially P-wave anisotropy.

The effect of near‐surface azimuthal anisotropy on a joint interpretation of seismic and electrical resistivity data

“…Shales are known to show significant elastic (Vernik and Liu, 1997; Bayuk et al ., 2007; Gong et al ., 2021) and electrical resistivity anisotropy (Hossain and Newton, 2014). As prior information, we were provided with shallow vertical seismic profiling (VSP) data acquired in the borehole located 300 m to the North from the studied site.…”