A proxy model of watercut in a given well with reservoir saturation s=\{ s_w, \, s_o, \, s_g \}:
| (1) | {\rm Y_{wm}} = \frac{1}{1 + \frac{M_{ro}}{M_{rw}} \cdot \frac{B_w}{B_o} } |
which provides a good estimate when the drawdown is much higher than delta pressure from gravity and capillary effects.
The model (1) can also be used in gross field production analysis and in this case the average reservoir saturation can be assumed homogeneous:
| (2) | s_w(t) = s_{wi} + (1-s_{wi}-s_{or}) \cdot \rm RF(t)/E_S |