Dynamic investigation of the effect of a relay ramp on simulated fluid flow: geocellular modelling of the Delicate Arch Ramp, Utah

A fluid flow simulation study was performed to investigate potential contrasts in reservoir performance between models displaying a soft-linked relay ramp vs. models with a continuous fault. The relay ramp model is based on a well-exposed outcrop analogue – the Delicate Arch Ramp, Arches National Park, Utah. In outcrop, the relay ramp exhibits a pervasive system of cataclastic deformation bands, which were mapped and incorporated into the reservoir simulation models. Several models were simulated, using deformation-band permeability as the main variable tested. Results show that when compared to flow across continuous faults, the presence of soft-linked relay ramps enhances net flow across the fault zone in all tested scenarios. Comparing models with deformation bands to the model that includes the ramp but no deformation bands illustrates that, although having an impact on flow tortuosity and sweep efficiency, deformation bands must have a very low permeability and be numerous before having a negative impact on recovery. Deformation bands with midrange permeabilities were shown to have a positive effect on recovery in the relay models, as they increase flow tortuosity and enhance sweep, causing later water breakthrough and prolonging production. Using very low-permeable deformation bands in the same models caused extremely poor pressure communication between the fault-breached compartments, despite the geometric connectivity provided by the sub-continuous relay beds.