The amount and distribution of residual oil saturation (ROS) are critical parameters for determining whether to apply an EOR process to a reservoir. A brief review of available ROS techniques is presented, indicating advantages, limitations, problems, and possible improvements of each technique. Advantages and disadvantages of each ROS-determination technique are summarized. Screening criteria for determining the best ROS technique under certain well bore or reservoir conditions are presented.This paper also presents results from comparisons of ROS measurements obtained from the literature as calculated from resistivity logs, pulsed neutron capture (PNC) logs, pressure coring, single-well tracer tests, nuclear magnetism logs (NML), carbon/oxygen (C/O) logs, and electromagnetic propagation tool (EPT) measurements. In this study, the ROS measured by each method is compared with that determined by other methods conducted in the same well. The comparison shows that average values of ROS determined by C/O log, PNC-LIL (log-inject-log), and single-well tracer test do not differ statistically when compared with other methods. The resistivity log tends to give higher than average [2 saturation units (s.u.)] ROS measurements, while pressure coring tends to give lower than average (4 s.u.) ROS values. EPT and NML show deviations of about 8 s.U. of ROS values from other methods, which indicates a statistically significant difference. ROS vertical profiles obtained by two different methods from the same well were compared to eliminate the ROS variation resulting from formation depth. The vertical profiles based on ROS zoning and foot-by-foot measurements were studied to provide more "resolution" for comparisons. The results show that discrepancies in measurement methods are more pronounced when vertical profiles are divided into different zones. This could mean that the discrepancies are much greater for some zones than for others. This approach offers the possibility of studying ROS-method discrepancies as a function of different ROS values.

An experimental study to investigate the influence of variations in test conditions and laboratory procedures on the electrical properties of rocks is presented. Results suggest that the cementation and saturation exponents in Archie's equation should be determined in the laboratory at near-reservoir conditions to prevent an error of up to 8% from being introduced during the determination of water saturation.

Improvements in reservoir characterization can greatly enhance reservoir performance predictions. Heterogeneity within most reservoirs, such as the Madison Group, can be better understood from integration of results from detailed core analyses. A fractured dolomite core sample from the Upper Madison Group, near Carter Creek gas field in southwest Wyoming was studied in detail to supplement the current methodology for delineating heterogeneities in core samples. Directional permeability, fracture system orientation, and other heterogeneities related to the core sample fabric were determined and quantified by studies of: impregnated thin-sections and use of computed tomography x-ray intensity, x-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Computed tomography (CT) is a fast, nondestructive, qualitative and quantitative tool for the evaluation of fracture systems and associated mineralogy. The scanning procedure employed involved assigning a density range that would highlight minerals having characteristic CT densities. This procedure helped to identify variations of fracture infilling materials. The core analyses data were integrated with the regional geology, downhole logs, and production data for final evaluation.

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Comparl son of the isoperms obtained by the parametric method with the isoperms plotted byWith the advent of enhanced oil recovery the graphical contouringtechnique show that: (1) (EOR) methods such as chemical flooding, miscible the parametric method gives a more reliable fit gas displacementand thermal methods, thrf?e-phase to the data points than manual techniques, relative permeabilitydata are needed to predict because it is based on mathematicaloptimization performances of field applications. Complexity and therefore eliminates subjective bias and (2) of experimental and calculation procedures for the graphical contouring method reveals the three-phaserelative permeabilitymeasurements is fluctuation in the original data points and a primary reason why published data in this area possible smaller scale trends that may be ire limited. Furthermore,arbitrarymethods used significant. The functional form presented in ior analysis and graphical representation of this paper can be used to estimate three-phase these experimental data are affected to some relative permeabilityfrom displacement (unsteady extent by subjectivebias. state) core flood experimentalresults.