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 in a given well 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.
Model (3) requires accurate input on reservoir saturation.
The model (3) can also be used in gross field production analysis and in this case the average reservoir saturation can be assumed homogeneous:
| (4) | s_w(t) = s_{wi} + (1-s_{wi}-s_{or}) \cdot \rm RF(t)/E_S |