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Modelling the dispersion and attenuation of seismic waves in partially saturated rocks is important for quantitative interpretation of seismic data. To observe the partial saturation effects on modulus and attenuation, three sandstone samples with different porosities were used in the laboratory experiment. The samples were measured by ultrasonic testing system under different water saturation using drainage process. The experimental results show that the bulk modulus more rapidly increased at higher saturations (>80 per cent), and attenuation peaks could be observed. Then we develop a new partial saturation model based on Chapman's theory and poroelastic theory. The new model is consistent with the Gassmann equation when the water saturation is 0 or 100 per cent. By analysing the characteristic frequency, the new model can be concluded in the form of a standard linear solid model. A comparison of the new model with the White model and the measured data is conducted. The results show that the model performed well at predicting the effective bulk modulus and attenuation of the rock with different water saturation. Finally, we discussed the impact of frequency, fluids and pore structures on the new model. The results reveal that the new model will be helpful in discussing partial saturation in rocks. [ABSTRACT FROM AUTHOR]

For many geophysical problems it is important to understand the influence of clay on the elastic behaviour of the rocks. However, this is difficult to measure because the complex petrophysical characteristics of tight sandstones make it challenging to control the clay parameters in natural samples. In this study, we synthesized nine tight sandstones with different clay types and content. Ultrasonic measurements and theoretical simulations were then used to analyse the influence of clay on the elastic modulus of brine saturated samples. We found that the shear modulus of smectite-rich samples decreased drastically after saturation, while the decrease observed in kaolinite-rich samples was relatively low. We propose that the reduction in surface energy caused by surface-particle clay hydration is a common mechanism that leads to shear softening in both kaolinite-rich and smectite-rich samples. However, the contact deformation caused by cation hydration of smectite is the primary mechanism leading to greater shear softening of tight sandstones containing smectite. Although the differential Kuster–Toksöz model is based on idealized pore shapes, a dual-porosity scheme can be used to explain and simulate the shear softening of artificial clay-rich tight sandstones. [ABSTRACT FROM AUTHOR]