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The Impact of Stratigraphic and Facies Architecture on Flow in Carbonate Reservoirs; An Integrated Approach Using Comparative Modeling Techniques

Abstract

Many studies have illustrated the need for a more comprehensive understanding of the impact of geologic heterogeneity on flow in different carbonate reservoir types and production settings. However, published examples of subsurface and outcrop analogue modeling and simulation studies typically focus on a subset of heterogeneities that are specific to the reservoir, or outcrop, of interest. We use a combination of flow simulation and experimental design techniques to investigate the first-order control of facies architecture on flow, within a suite of models constructed to combine six different stratigraphic heterogeneities. The impact of geologic heterogeneity on flow is investigated for waterflood production strategies that promote either horizontal or vertical flow, with different fluid types and well placements, allowing for a comparison of the relative impact of the heterogeneities in different production scenarios. We find that oil production decreases as percentage barrier coverage increases along stratigraphic surfaces (e.g. cementation to form hardgrounds), concurrent with an increase in the relative impact of the other stratigraphic heterogeneities. Varying the size or lateral distribution of the cemented barriers indicates an uncertainty in production estimates of 10 – 40 %. We also find that the impact of stratigraphic heterogeneities is the same regardless of the presence, size and orientation of different facies architecture within the model. Including facies heterogeneities in our experimental design suggests that isotropic architectures, such as reefs or planar biostromes, are of low ranked importance. However, the orientation and size of ooid shoals has mid to high impact on production behavior. For example, shoals oriented perpendicular to the dominant flow direction will enhance sweep efficiency and recovery factor, while delaying water breakthrough. We find that the method used to model facies architecture (e.g. stochastic and deterministic algorithms versus surface-based property domain approaches) has little effect on flow behavior and simulated production results. Our results show that facies architecture is an important control on flow in carbonate reservoirs.