Comparison of lithology and net pay uncertainty between deterministic and geostatistical inversion workflows

Assessment of the uncertainty associated with net pay estimates can be made from inversion of seismic data, either using deterministic inversion followed by probabilistic interpretation, or directly with geostatistical inversion. The uncertainty from the deterministic workflow is higher than from the geostatistical workflow. The difference in uncertainty increases as the thickness of the reservoir beds decreases. However, the estimates of mean net pay are very similar, suggesting that deterministic inversion followed by a probabilistic interpretation is able to provide reasonable estimates even when the reservoir is seismically thin. The uncertainty in the detailed distribution of lithology and properties in 3D space is also higher in the deterministic workflow. This is because the geostatistical inversion is able to overcome, to some degree, the limited seismic bandwidth by integrating all of the available information, especially the rock physics properties of the different lithologies, simultaneously during the inversion.