Can mechanical failure in unconsolidated sands during hydrocarbon production result in flow barriers

Water injectors in unconsolidated sands often experience severe injectivity decline and premature failure. The formation of shear bands and compaction bands is a possible mechanism which can cause a flow barrier. Herein, we exploit an elasto-plastic bifurcation analysis in order to assess whether shear bands and compaction bands can form under realistic reservoir conditions. Since injection favors the formation of dilatant shear bands, we focus on the possible formation of compactant deformation bands during a preceding depletion period with the potential to severely impede flow during subsequent injection. A set of conditions is elaborated, and they indicate a low risk of localization as a consequence of hydrocarbon production. In fact, the possibility of localization reduces upon progressive depletion. An extensive sensitivity analysis shows that this conclusion continues to hold when varying the material parameters and initial stress conditions within a realistic range for subsurface conditions. This renders the sketched scenario of deformation bands acting as flow barriers unlikely under conditions typical of deepwater reservoirs in the Gulf of Mexico. The conclusion that localized deformation bands probably do not cause injectivity loss is reinforced since only compaction bands can reduce the permeability sufficiently to create effective flow barriers. They would form perpendicular to the major compressive principal stress, and in a normal faulting regime, this would result in bands with a low inclination angle to the horizontal plane. They would not adversely affect flow from or towards (vertical) wells in a reservoir.