Rock physics inversion for CO₂ characterization at Sleipner

We combine Full-Waveform Inversion (FWI) and rock physics inversion to provide quantitative estimates of CO₂ saturation at Sleipner. The rock physics tool is based on uniform saturation and patchy saturation rock physics models. The patchy saturation model takes into account the attenuation at the mesoscopic scale. The uniform saturation model uses an effective fluid phase plugged into the Biot theory. The latter model will be mainly used in the Sleipner case. The rock physics inversion is implemented using an oriented Monte Carlo method (neighbourhood algorithm). We generate P-wave velocity using the FWI technology and then invert selected rock physics parameters using the rock physics inversion tool. The methodology is applied to both synthetic and real datasets. We propose a method to extract the baseline frame properties using P-wave velocity combined with S-wave velocity and density. We estimate the CO₂ saturation using P-wave velocity model derived from 2D FWI and evaluate the associated uncertainty. We show that the CO₂ saturation at Sleipner can reach 90% with an uncertainty of 0.1 to 0.2. We estimate a Brie exponent, which is describing the distribution type, ranging between 5 and 25, which indicates that the mixture is between patchy and uniform saturation.