Hierarchical modeling of multi-scale flow barriers in channelized reservoirs

Channelized reservoirs often show multi-scale architectures such as large-scale channel belts, middle-scale single channels and small-scale channel infill facies. These architectural elements are defined between bounding surfaces. Along these hierarchical bounding surfaces, thin shale drapes may be present as flow barriers that compartmentalize the reservoirs. Since the distribution of shale drapes are governed by the bounding surfaces of multi-scale architecture elements, they represent multi-scale heterogeneities. Characterizing the distribution of these multi-scale flow barriers calls for a hierarchical modeling approach in which the large-scale reservoir architecture is modeled first, the shale drapes are then simulated within this architecture framework. The reservoir architecture modeling in this paper involves defining channel deposition fairways (valleys) based on seismic data, modeling long sinuous channels and placing them into defined fairways such that all data are matched. The criteria for choosing a modeling approach include the ability to match hard data, to define object (channel) boundaries (for the purpose of attaching shale drapes), to reproduce a given stacking pattern and to be CPU efficient. This paper adopts a stratigraphic-based modeling approach. In this stratigraphic-based approach, individual channels are simulated using the YACS method (Alapetite et al., 2005). This method is fast and conditions to well data under the assumption that channel sand can be identified in the well data. To put multiple channels together reproducing desirable stacking patterns, the overlap ratio and migration ratio are simulated. The two parameters are typically used by geologists to describe the channel geometry. The overlap ratio provides the information of vertical overlap between channels, while the migration ratio describes the lateral overlap information between channels. Once the large-scale reservoir architecture is modeled, the