Investigating uncertainties in relative permeability measurements

In this article, relative permeability measurement methods for water-oil systems mimicking displacement processes in porous media when reservoir pressure is supported by an active aquifer or a water injection scheme are compared. The measurement methods are compared within the context of reservoir wettability. It is suggested that for reservoirs with predominant water-wetness, unsteady-state experiments could be run under the suggested Peters and Khataniar (1987) stability criteria. Steady-state experiments could also be run for comparative and in turn quality control purposes. In addition, a combination of unsteady-, steady-state and centrifugal experiments could be adopted to generate trustful results for reservoirs with intermediate wettability, but only if one has a reliable initial relative permeability to oil (k_ro) at a representative initial water saturation (S_wi). As such, it is recommended to use an unsteady-state technique for the initiation of the displacement experiments, a steady-state method for mid-range saturations, and the centrifuge for tail-end saturations. It should be noted that for the centrifugal method, comparable centrifugal and viscous forces are required to mimic displacement processes. Coyne's procedure could also be used for comparative and quality control purposes.