The impact of fault envelope structure on fluid flow: A screening study using fault facies

Structural elements of deformation-band fault zones are implemented as volumetrically expressed building blocks, that is, fault facies, in a series of synthetic reservoir geomodels and simulation models. The models are designed and built to reproduce a predefined range of fault system configuration, sedimentary facies configuration, and fault zone architecture. Using petrophysical properties derived from published field studies, the geomodel realizations are run in a reservoir simulator to monitor reservoir responses to variations in modeling factors. The modeled fault zones act as dual barrier-conduit systems, resulting in simulation models that can capture contrasting waterfront velocities, changes in waterfront geometries, and flow channelizing and bifurcation in the fault envelopes. The simulation models also show the development and sweep efficiency of bypassed oil and poorly swept regions because of the presence of the fault zones. Statistical analysis reveals that the fault facies modeling factors can be ranked according to impact on reservoir responses in the following descending order: fault core thickness, the type of displacement function, sedimentary facies configuration, the fraction of total fault throw accommodated by fault core and damage zones, fault system configuration, and maximum damage zone width. Fault core thickness is the most important factor because it governs the space available for fluid flow in the fault-dip direction. Other modeling factors affect the reservoir responses by controlling the geometry and continuity of fluid flow paths in the modeled fault zones.