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Porous siliciclastic reservoirs are known to contain structural heterogeneities such as deformation bands, which fall below current seismic resolution and which generally cannot be explicitly represented in reservoir models because of the prohibitively high computational cost. In this study, we built a reservoir model to evaluate fluid flow across a contractionally folded unit containing deformation bands (the Navajo Sandstone in the San Rafael Reef monocline, Utah). Using field data, geometric relationships, and auxiliary computational techniques, we upscale deformation bands to capture flow effects in the large-scale structure, running simulations with variable scenarios of permeability contrast between host rock and deformation bands. Our simulations show that pervasive deformation band arrays (such as the ones present in the monocline) have effects when the contrast of permeability between them and the host rock is of at least three orders of magnitude, delaying water breakthrough and enhancing sweep; in long-term production, this results in larger final produced volumes and higher total recovery. Because of the wide range of deformation band permeabilities used in this study, our findings can be of importance for the prediction of flow and optimization of production strategies in comparable traps and reservoirs. Additionally, auxiliary computational techniques and geometric relationships such as the ones presented in this study can significantly improve the incorporation of small-scale features with strong scale gap into conventional sized reservoirs.