$6\mathrm{.}1$ Using the letter symbols for reservoir engineering, write expressions for the following terms for a volumetric, undersaturated reservoir:

$($a$)$ The initial reservoir oil in place in stock$-$tank barrels

$($b$)$ The fractional recovery after producing $N_p$ STB

$($c$)$ The volume occupied by the remaining oil $($liquid$)$ after producing $N_p$ STB

$($d$)$ The SCF of gas produced

$($e$)$ The SCF of initial gas

$($f$)$ The SCF of gas in solution in the remaining oil

$($g$)$ By difference, the SCF of escaped or free gas in the reservoir after producing $N_p$ STB

$($h$)$ The volume occupied by the escaped, or free, gas