The importance of oil in the world economy cannot be overstated, and
methods for recovering oil will be the subject of much scientific and
engineering research for many years to come. Even after the application
of primary depletion and secondary recovery processes (usually
waterflooding), much oil usually remains in a reservoir, and indeed in
some heterogeneous reservoir systems as much as 70% of the original oil
may remain. Thus, there is an enormous incentive for the development of
improved or enhanced methods of oil recovery, aimed at recovering some
portion of this remainil)g oil. The techniques used range from
'improved' secondary flooding methods (including polymer and certain gas
injection processes) through to 'enhanced' or 'tertiary' methods such as
chemical (surfactant, caustic, foam), gas miscible (carbon dioxide, gas
reinjection) and thermal (steam soak and drive, in-situ combustion). The
distinction between the classification ofthe methods usually refers to
the target oil that the process seeks to recover. That is, in 'improved'
recovery we are usually aiming to increase the oil sweep efficiency,
whereas in 'tertiary' recovery we aim to mobilise and recover residual
or capillary- trapped oil. There are a few books and collections of
articles which give general overviews of improved and enhanced oil
recovery methods. However, for each recovery method, there is such a
wide range of interconnected issues concerning the chemistry, physics
and fluid mechanics of flow in porous media, that rarely are these
adequately reviewed.
