The vertical sweep efficiency is a function of the vertical heterogeneity (layering) and the mobility ratio (''M''). The mobility ratio defined here is the ratio of the [[relative [[permeability]]]] to water at ''S''<sub>or</sub> (''k''<sub>rw</sub>) to the relative permeability of the oil at ''S''<sub>wi</sub> multiplied by the oil-water viscosity ratio (''μ''<sub>o</sub>/''μ''<sub>w</sub>) as expressed in the following equation: | The vertical sweep efficiency is a function of the vertical heterogeneity (layering) and the mobility ratio (''M''). The mobility ratio defined here is the ratio of the [[relative [[permeability]]]] to water at ''S''<sub>or</sub> (''k''<sub>rw</sub>) to the relative permeability of the oil at ''S''<sub>wi</sub> multiplied by the oil-water viscosity ratio (''μ''<sub>o</sub>/''μ''<sub>w</sub>) as expressed in the following equation: |