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Organic shales can split into laminae or thin layers due to their fissility and are usually characterized as transverse isotropic (TI) medium. Understanding their elastic and anisotropic properties plays a significant role in geophysical modeling and imaging, reservoir geomechanics, and reservoir characterization. Ones can obtain their velocity anisotropy through laboratory and field measurements or rock-physics models. However, the measurements are scarce, and theoretical modeling of Thomsen’s anisotropy parameters generally requires extra inputs, which are sometimes difficult to obtain. This paper compiled ultrasonic data of 159 self-sourced reservoir shale samples from literature and our own measurements. Simple exponential models can capture the trends of the P- and S-wave anisotropy parameters, ε and γ, decreasing with increasing vertical P- and S-wave velocities, with R2 being above 0.84. The error in estimated anisotropy is small for high-velocity ( Vp0 > 4 km/s) shales but relatively large for low-velocity ( Vp0 < 4 km/s) shales. We analyze the influences of multiple geological factors on the proposed anisotropy-velocity relationships. We observe that the velocity anisotropy generally increases with clay content. In addition, mature shales (0.6 < Ro (%) < 1.4) generally have stronger anisotropy strength spreading in a broader range than overmature ones (Ro (%) > 1.4). Overall, no single parameter dominates the source of velocity anisotropy, which is jointly affected by the coupled factors of clay content, organic matter, porosity, maturity level, and geological history. The empirical model has the potential to offer a fast and straightforward method of predicting P- and S-wave anisotropy strength from vertical P- and S-wave velocities.

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