Remaining Oil Saturation Determination in Dukhan Arab C and Arab D Reservoirs

The Dukhan Field Arab C and Arab D Jurassic reservoirs have been developed via natural depletion followed by peripheral water injection of variable salinity waters. Additionally, the Arab D crestal development has been influenced by the expansion of the primary gas cap and subsequent gas cycling project. Six wells were recently drilled, cored and logged in areas of the reservoir that had been partially swept by water with the objective to quantify the remaining oil saturation (ROS) at these locations. Data acquisition to determine the oil saturations consisted of coring and acquiring a comprehensive logging suite comprised of resistivity, induction, dipole sonic imager, sonic scanner, electric imager, nuclear-magnetic resonance, and dielectric. The coring utilized low-invasion methods, with deuterium oxide tracer, to assess the degree of invasion. The cores were analyzed for routine properties and by Dean Stark analysis for ROS. Core description was done at a thin section and macroscopic level. Wellbore salinity samples from separate flow units were obtained to characterize the water in the swept zone to assist in evaluation of the water saturation from the logs. Following collection of the data, analysis was performed to: • Integrate the core and log saturation data to develop most likely estimates of ROS. • Examine the impact of throughput using reservoir simulation models. • Assess remaining oil saturation by reservoir, zone, and rock type. • Assess the uncertainty and establish ranking criteria in ROS measurements. ROS from high-quality deep resistivity logs using true formation water salinity data provided the most likely measure of ROS at reservoir conditions. The integrated analysis resulted in a consistent set of ROS measurements grouped by zones and rock types. This dataset can be used for additional studies identifying future opportunities for improved recovery from the reservoirs.