Are relay ramps conduits for fluid flow? Structural analysis of a relay ramp

Abstract: Relay ramps associated with overlapping faults are commonly regarded as efficient conduits for fluid flow across potentially sealing intra-reservoir fault zones. The current study demonstrates that structural heterogeneity n the often anomalously wide damage zone of relay ramps may represent potential baffles to intra-ramp fluid flow. A network of ramp-parallel, ramp-diagonal and curved cataclastic deformation bands causes compartmentalization of the ramp studied in Arches National Park, Utah. Harmonic average calculations demonstrate that, although single deformation bands have little or no effect on effective permeability, the pre-sence of even a very small number of low-permeable d formation band clusters could reduce along-ramp effective permeability by more than three orders of magnitude. Thus, although relay zones may maintain large-scale geometric communication, the results of this study demon-strate that caution must be exercised when considering relay ramps as fluid conduits across ealing faults in a production situation. Although relay ramps clearly represent effective migration pathways for hydrocarbons over geological time, the extent towhich they conduct fluids in a pro-duction situation is more uncertain. Quantitative approaches include adjusting the transmissibility multipliers for faults in reservoir models to allow for increased cross-fault flow. If, however, th