Comparing the uncertainties inherent to different reservoir rocktyping methods for a giant carbonate reservoir

Abstract

We apply, evaluate and compare several reservoir rock typing (RRT) approaches for a giant carbonate reservoir in the Middle East that is characterized by poor rock quality and a thick transition zone. These workflows are used to define RRTs by comparing several approaches, namely pseudo clouds from porosity and permeability data for each subzone, global hydraulic elements, petrophysical grouping using MICP data and Lucia classes. Then, the permeability models obtained from each RRT approach are used as input data for building the water saturation models using two different approaches, Leverett J-functions and the Geo2Flow software. The application of this workflow leads to a significantly change of the saturation distribution and subsequently revised the oil-in-place estimation for the field, especially because the reservoir has a thick transition zone. The variations in saturation distributions and oil-in-place arising from the different RRT approaches are likely larger than the uncertainty in the geological data itself. The saturation distributions do not only impact oil-in-place estimates but also predictions for the subsequent reservoir simulation models.