Which sub-seismic heterogeneities influence waterflood performance? A case study of a low net-to-gross fluvial reservoir

Abstract Waterflood performance in a fluvial reservoir is examined to assess which aspects of the reservoir are important to describe for accurate simulation of recovery performance. The study is based on a low net-to-gross fluvial reservoir and we consider the influence of sedimentary heterogeneities which are sub-seismic-scale in a full-field model. A detailed hierarchical 3D geological model is developed and flow properties are upscaled. Particular attention is given to representing the influence of cross-stratification. A screening study is then conducted to assess which heterogeneities and scales have the greatest influence on recovery predictions. By using experimental design the influence of a large number of factors is examined in an efficient manner. The results show that parameters describing channels and channel belts have the greatest influence. Somewhat surprisingly, the number of channels in a belt and their width and thickness has at least as much influence on sweep efficiency as net-to-gross and the stacking of belts. In addition to the influence of these large-scale heterogeneities, capillary effects at the laminae scale within cross-stratification have a significant effect on recovery. Early identification of important heterogeneities will allow for more efficient field exploitation. The strongest impact of this approach may be to focus data collection early in the life of a field on the most important types of heterogeneities to be expected for a given depositional and stratigraphic setting.

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