Toward Quantitative Remaining Oil Saturation (ROS): Determination Challenges and Techniques

Abstract

Abstract Remaining Oil Saturation (ROS) is a crucial input to reservoir development projects. Determination of such a time-dependent parameter assists the evaluation of the sweep efficiency, provides calibration points for simulation models and also sets the basis for future workover and EOR projects. Quantification of ROS in waterflooded areas has always been a known challenge to resistivity-based techniques. The mixed water salinity environment, due to differences between original connate water and injected water, and the impact of the imbibition process on the saturation exponents are the main hindrances. Over the past few years, data acquisition strategies have been deployed to overcome these challenges. The strategies include in-situ measurements that are insensitive to water salinity and to fluid displacement processes, such as Nuclear Magnetic Resonance in Log-Inject-Log mode, Carbon/Oxygen, and Dielectric logs. Extensive wireline formation testing programs usually follow to confirm the findings from the aforementioned measurements. Depending on the well's criticality, special coring programs might also be included such as sponge coring or liquid trapper. Special planning and standardization efforts are necessary for such extensive data acquisition programs to ensure data quality and consistency. This paper presents Saudi Aramco data acquisition strategies for ROS applications. It also highlights the main challenges and the technologies deployed to resolve them. Advantages and limitations of these technologies are reviewed. Lastly, our ongoing efforts to reduce the uncertainties of such analyses are presented.