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Experimental investigation of the elastic behaviours of lacustrine shales remains sparse, although they play an essential role in source rock evaluation, unconventional reservoir exploration and development, and the seal integrity evaluation for geological storage of CO2 and nuclear waste disposal. We make the ultrasonic velocity measurement of 63 organic‐rich shale samples (Chang 7, Qingshankou and Lucaogou formation) from three typical lacustrine basins in China. It is found that the P‐ and S‐wave velocity of Chang 7 and Qingshankou shale corresponding to the fresh‐brackish lacustrine depositional environment is mainly impacted by the clay and organic matter content, whereas their elastic anisotropic magnitude is mostly influenced by clay content. The P‐ and S‐wave velocities of Lucaogou shale corresponding to the saline lacustrine depositional environment are mainly affected by the total organic carbon and porosity and exhibit weak anisotropy linked to organic matter enrichment. Exponential law well captures the relationship between anisotropic magnitude and velocity perpendicular to bedding for both saline and fresh‐brackish water lacustrine shales, although there exists notable discrepancy, particularly at low velocities. The disparity in elasticity between laminations has a profound impact on the magnitude of elastic anisotropy and shapes the trend of velocity variations. [ABSTRACT FROM AUTHOR]

To improve our understanding of wave dispersion and adsorption signature of organic shales, we select a set of vertical shale samples cored from different formations and conduct the forced-oscillation measurements in seismic frequencies of 2–800 Hz at the oven-dried conditions. The results demonstrated that both Young's modulus and Poisson's ratio of immature Barnett and Eagle Ford shales and mature Mancos shale remain roughly constant and the extensional attenuations are also insignificant at the entire frequency band. However, the mature Jungar shale exhibits strong dispersions with the magnitude of 23.4 per cent for Young's modulus at the confining pressure of 3.4 MPa. The dispersion and magnitude of Jungar shale overall exhibit a decreasing trend with increasing pressure, but still maintain strong attenuation at the confining pressure of 20.8 MPa. It is found that the single parameter of TOC, thermal maturity and clay content are not the controlling factors of wave dispersion and adsorption signatures. Instead, the geochemical index |${\rm{TOC}} \times {S_1}/({S_1}{\rm{ + }}{S_2})$| is positively correlated with dispersion and attenuation magnitude, suggesting that organic richness and maturity level jointly control the wave adsorption characteristics. Geochemical analysis and phenomenological modelling imply that such kinds of energy dissipation in organic shales are possibly caused by the viscous friction at interfaces between inorganic grains and the surface of liquefied or bitumen-filled organic matter. Besides, a modified standard linear solid model containing multiple sets of a characteristic frequency is proposed and well captures the continuous dispersion signatures considering that the Jungar shale contains various maturity-induced viscous organic matter. [ABSTRACT FROM AUTHOR]