Seismic Fluid Identification Considering Pore Structure Effects

Saturated rocks typically contain pores of various geometric shapes. The complex pore structure not only significantly affects the elastic and seismic response characteristics of rocks but also influences the accuracy of petrophysical parameter predictions. Existing rock physics inversion methods struggle to quantitatively describe pore type distributions and their geological implications, and there remains a lack of comprehensive inversion methods for simultaneously determining pore types and petrophysical parameters in porous reservoirs. Porosity, pore structure, and fluid properties collectively reflect the reservoir's physical attributes, pore space complexity, and pore fluid types. Establishing an accurate relationship between seismic parameters and reservoir pore characteristics can enhance the reliability of reservoir predictions. In this paper, taking the oil and gas-bearing sandstone reservoir as an example, the influence of reservoir pore space geometry on rock elastic parameters and seismic AVO reflection coefficients is theoretically considered from the perspective of seismic petrophysics, and the relationship between seismic reflection coefficient and effective pore structure is established. By combining the Biot-Gassmann pore theory and Russell's linear approximation equation, a target functional containing the fluid term and pore structure was derived. Based on the stochastic inversion algorithm, the inversion of the fluid term and pore structure is stably achieved.