Greater-than-one relative permeability in mixed-wet limestone

Waterflood relative permeability was measured in Indiana limestone under five mixed-wet conditions, as characterized by macroscopic contact angles on polished calcite which ranged from 0w = 55° to 150°, and two Darcy velocities: Uw = 1.5 μm/s and 30 μm/s. Oil relative permeability at initial oil saturation decreased and brine relative permeability at residual oil saturation increased with increasing 0w under the conditions considered presently. Greater-than-one end-point relative permeability was observed at 0w < 90° for oil and at 0w > 130° for brine. End-point brine relative permeabilities were larger at the larger Uw under all oil-wet conditions considered, i.e., 0w > 90 ̊. In contrast to recent literature that associate greater-than-one permeability to the flow of non-wetting fluid against surface, we observed enhanced permeability even when the flowing fluid was the wetting phase. Our results demonstrate that models assuming kr ≤ 1 underestimate fluid displacement for a wider range of contact angles than previously documented.