As more and more fields mature in their production life cycle, EOR/IOR methods attain increasing significance. To plan these recovery methods optimally an accurate measure of the remaining hydrocarbon saturation is required to establish if there are sufficient hydrocarbons left in the reservoir to make a recovery process worthwhile. Integrating the state of the art Liquid Trapper coring technique and laboratory analysis on whole core and plugs reduce the uncertainty in this crucial reservoir parameter. New developments in dielectric logging techniques provide accurate remaining saturation answers with depth resolution of the scale of core plugs, for effective comparison and enhanced confidence on the answers.
The current study aims to evaluate the remaining oil saturation (ROS) after a water flood in 4 different wells located in a depleted zone of a Cretaceous carbonate reservoir in a giant field, onshore Abu Dhabi. This is the first time a multi-well study involving liquid trapper technique is conducted in the subject field with an objective of better capturing the reservoir heterogeneities and their possible impact on the ROS.
Laboratory measurements were conducted on reservoir core samples ranging from full diameter whole cores down to small plugs. The multi-scale analysis confirmed the variations in rock properties and the influence of heterogeneity on the reservoir properties, and ROS distribution. Petrophysical Groups (PG) were also defined and the final ROS values were distributed per PGs. ROS values from cores were compared with the continuous log measurement from the new multi frequency dielectric tool, deployed for the first time in the country. The array sensors of the tool make the borehole correction robust while the dispersion analysis of the multi-frequency data provides saturation answers unaffected by pore fluid salinity and carbonate texture. The uncertainty in ROS measurements and best practices for future is also discussed.