Numerical modeling of fault damage zones and their impact on EOR applications

Resumo

Geological faults are present in several regions in subsurface. For conventional reservoir engineering in the oil and gas industry, such faults are considered as impermeable surfaces responsible for reservoir compartmentalization. However, seismic and field observations show that faults are not surfaces but volumes composed by two regions: the fault core and the damage zone. While the fault core accounts for the fault sealing, the damage zone can have different impacts for fluid flow depending on the geological structures present around the fault. Porous host rocks such as sandstones are prone to trigger deformation bands which can significantly reduce the permoporous properties of the rocks, acting as barriers for fluid flow. On the other hand, stiff rocks with reduced porosities are prone to develop fracture networks in the damage zone, creating preferential flow paths. Therefore, the consideration of fault damage zones and their corresponding properties are important for reservoir modeling in order to develop suitable production strategies, in particular for enhanced oil recovery. In this kind of applications, water is injected into the reservoir aiming at raising both the reduced reservoir pressure and the oil production. In this study, we consider a three-dimensional reservoir model that includes a water injection well, an oil production well and fault damage zones between the wells. Then, different scenarios are analyzed considering the fault damage zone composed either by deformation bands or fracture networks using equivalent continuum approaches. For such purpose, power-laws based on deformation band density and fracture intensities around the fault core are used to define the permeabilities corresponding to the damage zone. The numerical results show that the presence of the damage zone generated around a normal fault changes the water propagation speed, affecting the oil recovery efficiency. Furthermore, the obtained results also contribute for a better understanding the dynamic behavior of flow through these geological structures.