Simulation of Heterogeneous Sandstone Experiments Characterized Using CT Scanning
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Coreflood experiments in naturally heterogeneous sandstone outcrop cores have been conducted and then simulated. The displacements included waterfloods and polymerfloods using tracers for the oil and/or water during both single-phase flow and two-phase flow. Those involving the displacement of viscous polymer solution were unstable. The cores were characterized by a combination of air permeability measurements on each square centimeter of each face, CT scans of cross-sections of the core spaced one centimeter apart along the length of the core and by multiple water and oil tracers. Fine-grid simulations were then made using these characterization data as input and comparisons made with pressure, tracer, saturation distribution and production data from the corefloods. The agreement between the experiments and simulations is good. This work highlights our efforts to use numerical simulation to analyze our own experimental data on the naturally heterogeneous Antolini sandstone cores. The cores were used in the CT scanner-assisted study of the effects of heterogeneity on miscible and immiscible displacement. An important factor that distinguishes our work from other results reported in the literature is the use of an outcrop sandstone rather than either artificially heterogeneous cores or small samples of reservoir cores. We used an integrated approach that includes experiments using an air minipermeameter, CT scanning, multiple tracer experiments in both water and oil, pressure data, oil recovery data and both stable and unstable polymer displacements in large samples of heterogeneous outcrop sandstone combined with fine-mesh simulations using the characterization data. In this study two CT scanner-assisted corefloods were performed and were simulated using the compositional chemical flooding simulator UTCHEM. A polymerflood experiment at waterflood residual oil saturation was also simulated. We modified UTCHEM, enabling the input of initial brine, residual brine and residual oil saturation distributions in the simulations. For the first time displacements in heterogeneous cores were realistically simulated using a representative porosity, permeability, residual brine and oil saturation distributions using the fine-scale characterization data. Using the available experimental data, the rheology of a hydrolyzed polyacrylamide polymer solution was simulated. These simulations have enabled us to make quantitative use of these characterization data, aiding our understanding of these data and the flow processes that occur in heterogeneous media, and are a first step in testing scaleup procedures. Very few experiments reported in the literature are comparable to those in this study, i.e., displacements using well characterized, naturally heterogeneous media. These results have become a starting point for other simulation studies, such as the viii investigation of the importance of polymer grading and use of effective properties derived from fine-scale characterization data, in the physical and numerical coarse-mesh simulations of displacements in heterogeneous sandstones.