Page 107 - Fundamentals of Enhanced Oil and Gas Recovery

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Enhanced Oil Recovery Using CO 2

on the basis of the thickness and orientation of the aquifer. Regardless of the type of
the aquifer, those reservoirs that are closed and disconnected from huge aquifers are
the most appropriate candidates for combined EOR and CO 2 storage operations.
This is because when CO 2 is injected into a reservoir, it needs to force out the
invaded water from the aquifer. As a result, injectivity is reduced compared to those
reservoirs with closed boundaries. Lastly, most probably an efficient storage would
occur in those reservoirs with a sealing structure at formation tops with less open fault
and fracture systems [88]. Selection criteria for an efficient CO 2 EOR and storage are
given in the relevant literature [32].
Commonly, a co-optimization function is defined for the combination of incre-
mental oil recovery and CO 2 storage to be maximized. Based on Kamali and Cinar
[89], this co-optimization function can be expressed as follows:

P
N p M CO2
f 5 w 1 1 w 2 1 2 I (3.27)
OIP M CO2
where N p is the net oil production, OIP stands for the oil in place at the start of CO 2
injection, M P shows the amount of produced CO 2 , and M I indicates the amount
CO2 CO2
of CO 2 injected. Obviously, the amount of stored CO 2 can be found by subtracting
M I from M P . The constants w 1 and w 2 are weighting factors for oil recovery and
CO2 CO2
CO 2 storage, respectively (0 # w 1 ,w 2 # 1 and w 1 1 w 2 5 1). If the aim is to maximize
oil recovery, then w 1 5 1, similarly for maximum CO 2 storage w 2 5 1. When both
aims are equally important, then w 1 , w 2 5 0:5.

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