Specific type of waterfflood recovery when offtakes are fully compensated by intakes  intakes: 

Instantaneous Voidage Replacement Balance (IVRB) = Intakes - Offtakes =  $//<![CDATA[ \begin{array}{l}\Delta q = q^{\downarrow}_t - q^{\uparrow}_t = 0\end{array} //]]>$ 

which is equivalent to: 

Instantaneous Voidage Replacement Ratio (IVRR) = $//<![CDATA[ \begin{array}{l}\displaystyle {\rm IVRR} = \frac{\rm Intakes}{\rm Offtakes} = \frac{q^{\downarrow}_t}{q^{\uparrow}_t}\end{array} //]]>$ = 1

See also

Petroleum Industry / Upstream /  Production / Field Development Plan / Recovery Methods / Waterflood Recovery (WF)