Ratio of water production rate at surface q_W to liquid production rate at surface q_L = q_O+q_W:
| (1) | Y_w=\frac{q_W}{q_L} |
It relates to Water-Oil Ratio (WOR) as:
| (2) | Y_w=\frac{1}{1+q_O/q_W}=\frac{{\rm WOR}}{1+{\rm WOR}} |
The simplest way to model the watercut is the Water Fractional Flow:
| (3) | {\rm Y_{wm}} = \frac{1}{1 + \frac{K_{ro}}{K_{rw}} \cdot \frac{ \mu_w}{\mu_o} \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.
In case the reservoir saturation is not known one can assume a homogeneous reservoir saturation model:
| (4) | s_w(t) = s_{wi} + (1-s_{wi}-s_{or}) \cdot \rm RF(t) |