Using Residual Oil Saturation (Sor) to Reduce Uncertainty in Reservoir Modeling - A Case Study

Abstract

Abstract Residual hydrocarbon saturation is one of many important inputs necessary to have an accurate dynamic model. It is defined as the remaining hydrocarbon after the reservoir has been fully flooded. An Sor study has been performed in one of the major carbonate fields onshore Abu Dhabi UAE. The hydrocarbon is oil and the flooding fluids are water and lean gas. The residual oil saturation to both water flooding (Sorw) and to gas flooding (Sorg) were calculated. The determination of Sor is one of the most difficult Petrophysical parameters to be precisely determined in carbonate reservoirs due to their high degree of heterogeneity. In this study we applied practical methods using all available data such as Core data (Sponge core, Liquid trapper & Imbibitions SCAL), Cased hole PNS logs and Open Hole Resistivity logs. Pros and cons of each method will be addressed in the paper. A comprehensive data matrix & analysis was completed; results from different methods were compared to select the appropriate value to be used in the dynamic model. The impact of the Sor uncertainty on oil recovery was evaluated by performing an uncertainty analysis in the dynamic modelling, for example, an on-going major project which aims to assess the value of developing one of the most complex areas within the field. Uncertainty of both Sor to water and gas were evaluated by assigning ranges based on actual measurements. The study results lead to recommendations for additional field Sor measurements and data acquisition optimisation to reduce remaining uncertainties, which will be presented.