Ratio of water production rate at surface $\begin{array}{l}q_W\end{array}$ to liquid production rate at surface $\begin{array}{l}q_L = q_O+q_W\end{array}$ :

(1)	$\begin{array}{l}\displaystyle Y_w=\frac{q_W}{q_L}\end{array}$

(2)	$\begin{array}{l}\displaystyle Y_w=\frac{1}{1+q_O/q_W}=\frac{{\rm WOR}}{1+{\rm WOR}}\end{array}$

The simplest way to model the watercut Y_w in a given well is the Watercut (Yw) Fractional Flow @model:

(3)	$\begin{array}{l}\displaystyle {\rm Y_{wm}} = \frac{1}{1 + \frac{M_{ro}}{M_{rw}} \cdot \frac{B_w}{B_o} } = \frac{1}{1 + \frac{k_{ro}}{k_{rw}} \cdot \frac{\mu_w }{\mu_o } \cdot \frac{B_w}{B_o}}\end{array}$

which provides a good estimate when the drawdown is much higher than delta pressure from gravity and capillary effects.

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)	$\begin{array}{l}\displaystyle s_w(t) = s_{wi} + (1-s_{wi}) \cdot \rm RF(t)/E_S\end{array}$

This is a very simplistic proxy-model of reservoir saturation under an idealistic waterflood conditions and may mislead in specific cases.

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