Quantitative prediction of porosity and gas saturation based on a new dual-porosity rock-physics model and Shuey?s Poisson ratio for tight sandstone reservoirs

The prediction accuracy of physical parameters from seismic data has strong dependence on the quality of the used elastic parameters and rock-physics models especially for tight sandstone reservoirs. In this study, a new dual-porosity model with stiff and compliant porosities is firstly deduced from classical differential effective medium model according to the characteristics of both pores and fractures development in tight sandstones, it is the product of power function of both compliant and stiff porosities, and is independent of the addition order of pores. Then, the Shuey & rsquo;s AVO (Amplitude Variation with Offset) approximation is expanded, and a new Shuey Poisson & rsquo;s ratio which is the reciprocal of the difference between 1 and Poisson & rsquo;s ratio is defined and inverted from Shuey Poisson & rsquo;s ratio reflection seismogram to ensure the inversion accuracy of both P-wave impedance and ShueyPR. Next, a new two-dimension rock-physics template on P-wave impedance versus Shuey Poisson & rsquo;s ratio is built by the new dual-porosity model and Gassmann equations to characterize the quantitative rela-tionship between P-wave impedance, Shuey Poisson & rsquo;s ratio and physical properties and is used to invert the porosity and saturation through global optimization algorithm. The new method has been applied to quantitative reservoir prediction of tight sandstone of Shaximiao Formation of QL gas field in Northwest Sichuan, China. Real application indicates that the distribution of high-porosity reservoirs with porosity more than 8% and their gas saturation can be accurately predicted. <comment>Superscript/Subscript Available</comment