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

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can also be used in gross field production analysis and in this case the average reservoir saturation can be assumed homogeneous:

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

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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