Experimental investigation of mechanical compaction on the physical and elastic properties of synthetic shales

Abstract

Three sets of synthetic shale samples with different clay minerals were prepared to study the effects of mechanical compaction stress on the physical and elastic properties of shales. The results suggest that the physical and elastic properties (i.e., porosity, density, acoustic velocity, etc.) of the mudstones vary greatly the compaction stress, and the type of clay minerals. For a given compaction stress, the synthetic shale with kaolinite exhibits the smallest density and a highest porosity, while the sample with smectite shows the highest density and the smallest porosity. Further, the velocity demonstrates a considerable dependence to compaction stress, both P- and S-wave velocities in different directions increase with the compaction stress. We also find that the velocity anisotropy parameters increase with the compaction stress, and the S-wave anisotropy is more sensitive to the compaction stress compared to the P-wave anisotropy. With respect to the mechanical properties, the dynamic Young's modulus increase with the compaction stress, while the Poisson's ratio decrease with the compaction stress. This can be attributed to the decrease in the porosity. The results also indicate that the mechanical properties display obvious anisotropic behaviours. Finally, strong correlations are observed between the porosity and the velocity anisotropy and mechanical anisotropy for all the prepared samples, providing a means of estimating seismic anisotropy from porosity in shales.