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Summary

Coreflood experiments in naturally heterogeneous sandstone outcrop cores were conducted and simulated. 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 corn were characterized by polymer solution were unstable. The corn were characterized by air permeability measurements on each square centimeter of each face and by C.T. scans of cross-sections of the core spaced one Centimeter apart along the length of the core. Fine-grid simulations were then made using these characterization data as input. The agreement between the experiments and simulations is good. Simulations using coarser grid physical descriptions were then made using effective properties.

Introduction

The results given in this paper summarize our efforts to use numerical simulation to analyze our own experimental data on naturally heterogeneous sandstone cores called Antolini sandstone. Antolini sandstone is an eolian outcrop in northern Arizona. A series of displacements were conducted in two samples of this outcrop. Experiment Al is one of several corefloods done by Wreath to study polymerflooding in heterogeneous cores. Experiment Ahtolini-4 is one of several corefloods done by Ganapathy to study the effects of heterogeneity on both miscible and immiscible displacements. In both cases, the cores were characterized by a combination of air permeability measurements on each square centimeter of each face of rectangular slabs of sandstone, C.T. scans of cross-sections spaced one centimeter apart along the length of the cores ad by multiple water and oil tracers. Fine-grid simulations were then made using this characterization data ad comparisons made with the pressure, tracer and production data from these corefloods. The chemical flooding simulator developed at The University of Texas called UTCHEM was used for these simulations.

An important factor that distinguishes this 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 present an integrated approach that includes experiments using an air minipermeameter, C.T. 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 both fine-mesh and coarse-mesh simulations. The use of this particular outcrop sandstone for these and other similar experiments has a number of advantages over the use of reservoir cores because we can readily obtain large samples and as may samples as needed with variable degrees of heterogeneity. It also has advantages over artificially heterogeneous permeable media because as a practical matter samples of consolidated sandstone with large and practical matter samples of consolidated sandstone with large and variable heterogeneity on a variety of scales are difficult and expensive to make and may still not minic nature in some ways we may desire. For example, in addition to the macroscopic flow characteristics that are included in this paper, results of how the residual oil saturation differs between waterflooding and polymerflooding can be found in Wreath.