Shale elastic property relationships as a function of total organic carbon content using synthetic samples

• We have produced synthetic shale samples with controlling percentage of clay minerals, and TOC content in-situ stress conditions.
• P- and S-wave velocities of synthetic samples vary under isotropic stress conditions with respect to TOC and clay mineral content.
• The acoustic impedance trend tends to reduce as an increase in TOC content and clay mineral.
• Our approach enabled to introduce an equation that can be used to estimate TOC content of shale formations.

Understanding the main factors that control elastic properties of organic shale is crucial for exploration and successful gas production from unconventional reservoirs. Mechanical and dynamic elastic properties are important shale characteristics that are not yet well understood as there have been a limited number of investigations involving organic rich shale samples. Synthetic shale core samples whose clay mineralogy, non-clay mineral content and Total Organic Carbon (TOC) content are known can be used to study variations of elastic parameters in a controlled experimental environment including in-situ stress conditions.A total of 17 synthetic shale samples with different mineral composition and TOC percentage were created for our investigations under isotropic stressed and unstressed conditions. Ultrasonic transducers were used to measure body wave velocities, which were then used to calculate the elastic properties of different shale samples. The results demonstrate that P- and S-wave velocities vary under isotropic stress conditions with respect to the TOC and clay mineral content. It is shown that isotropic stress significantly impacts velocity and the velocities of P- and S-waves are inversely proportional to TOC content. In addition, the increase in the TOC content reduced density and increased shale porosity. This study presents equations that allow us to estimate shale TOC content using compressional and shear wave velocities and density.