Probabilistic Simultaneous Inversion of Vp/Vs Ratios Using Solely Zoeppritz Equation for PP-wave

We introduce a methodology for probabilistic calculation of the Vp/Vs ratios in layers 1 and 2 solely from calibrated PP seismic gathers without postulating Vp/Vs1 ratio to be known. We utilize the Zoeppritz equation for calculation of PP-reflection coefficients at an interface of two homogeneous, isotropic, elastic layers and invert it to estimate Vp/Vs1 and Vp/Vs2. This way we obtain all Vp/Vs1-Vp/Vs2 pairs that satisfy intercept-RC(angle) at each point of interest. Moreover, we calculate statistical parameters such as standard deviation at each point. By doing so, we create uncertainty maps which can yield useful information about quality of data and depict zones of unreliable data. We test the methodology in the Barents Sea gas reservoir. It serves as an alternative to reflectivity-based AVO screening during early exploration, opening up for more quantitative interpretations without going to more cumbersome simultaneous AVO inversion which requires good well ties and a reliable low-frequency model.