Effect of pore structure on the dispersion and attenuation of fluid-saturated tight sandstone

Abstract

The pore structure of tight sandstone has an important effect on its elastic properties, and also determines the fluid-flow-related wave dispersion and attenuation mechanisms. However, in these dispersion models, only compliant pores with a fixed aspect ratio and content have been considered, which is not completely realistic in reservoir rock. A procedure is presented to obtain the pore aspect distribution of compliant pores (cracks) from the pressure dependence of the velocities. Based on the pore aspect distribution of the compliant pores, Gurevichs squirt-fluid model is modified to consider the complex pore structure of reservoir rocks. The extended Gurevich squirt-flow model is consistent with Gassmanns equation at the low-frequency limit, and with the MavkJizba model at high frequency. To illustrate the validation of the extended Gurevich squirt-flow model, we compare the predictions of our squirt model with the laboratory measurements of two examples of water-saturated tight sandstone at ultrasonic frequency. On the basis of the pore structure, the new model is more accurate in predicting the pressure dependence of the compression and shear velocities for these two samples. Considering the aspect ratio distribution of compliant pores in the tight sandstone samples, the new model for predicting the dispersion curve shows a relatively wide squirt-flow relaxation frequency range, which even covers the typical seismic frequency and sonic logging frequency. This observation indicates that squirt-flow may be important, even in the typical seismic exploration frequency for tight sandstone with a special pore structure.