Simultaneous prediction of geofluid and permeability of reservoirs in pre-stack seismic inversion

Geofluid discrimination and permeability prediction are indispensable steps in reservoir evaluation. From the perspective of pre-stack seismic inversion, predicting fluid indicators is an effective method for obtaining fluid properties directly from seismic data. In contrast, the direct prediction of permeability from observed seismic gathers is constrained by the difficulty in establishing a link between permeability and elastic parameters. However, we show that the pore structure parameters in seismic petrophysical theory are highly related to permeability, providing a new solution for predicting permeability using seismic data. Therefore, the correlation between the shear flexibility factor and permeability is first verified based on logging curves and laboratory data, and the results demonstrate that the shear flexibility factor can give an indicator of reservoir permeability. Secondly, an approximate reflection coefficient equation is derived for the direct characterization of the shear flexibility factor. In the proposed equation, a novel fluid indicator, expressed as the ratio of Russell’s fluid indicator to the square of the shear flexibility factor, is defined for the simultaneous prediction of fluid types and permeability. With the validated response of the novel fluid indicator to geofluid types, we achieve simultaneous predictions of fluid types and reservoir permeability characteristics from pre-stack seismic data, employing a boundary-constrained Bayesian inversion strategy. The model tests and the application on field data from a clastic reservoir confirm the effectiveness and applicability of the method.