Abstract
This paper presents applications of deterministic and geostatistical reservoir characterization methods to the heterogeneous carbonates of the upper Shuaiba formation in Daleel field, Oman. High resolution reservoir descriptions based on the integration of logs, core, pressure transient tests, geology and seismic data are constructed; and properly upscaled for use in reservoir simulation models in history matching of field performance data. Deterministic descriptions utilize three and six layer models to assess the impact of layering heterogeneity on reservoir performance. Conditional geostatistical methods of SGSIM and SISIM with and without explicit modeling of geology generate fine-scale realizations of porosity and hydraulic flow units, which are then used to construct permeability and initial water saturation distributions. Permeability heterogeneity is upscaled to coarse-scale simulation gridblocks by an improved upscaling method based on an upstream-weighted interblock transmissibility algorithm.
The study shows that detailed and concise reservoir descriptions result in history matches that are more consistent with a variety of measured data. Generally, geostatistical techniques combined with geology and proper upscaling of permeability heterogeneity yield best results without artificial alterations in various fluid and rock properties. Although acceptable history matches could be obtained with less detailed reservoir descriptions, these required modifications to fluid and rock data beyond reasonable ranges, illustrating the need for detailed reservoir characterization.
