EXPLORATION, RECOVERY, AND TRANSPORTATION 83
In these reservoirs it is desirable to initiate enhanced oil recovery (EOR) operations as early as possible. This may mean considerably abbreviating conventional secondary recovery operations or
bypassing them altogether. Thermal floods using steam and controlled in situ combustion methods are also used. Thermal methods of recovery reduce the viscosity of the crude oil by heat so that
it flows more easily into the production well. Thus tertiary techniques are usually variations of secondary methods with a goal of
improving the sweeping action of the invading fluid.
Enhanced oil recovery methods are designed to reduce the viscosity of the crude oil (i.e. to reduce the pour point of the crude oil
relative to the temperature of the reservoir), thereby increasing oil
production. Enhanced oil recovery methods are applied started
when secondary oil recovery techniques are no longer enough to
sustain production. The oil remaining after conventional recovery
operations is retained in the pore space of reservoir rock at a lower
concentration than originally existed. In portions of the reservoir that
have been contacted or swept by the injection fluid, the residual oil
remains as droplets (or ganglia) trapped in either individual pores or
clusters of pores. It may also remain as films partly coating the pore
walls. Entrapment of this residual oil is predominantly due to capillary and surface forces and to geometry of the pore systems.
Enhanced oil recovery processes use thermal, chemical, or fluid
phase behavior effects to reduce or eliminate the capillary forces
that trap oil within pores, to thin the oil or otherwise improve its
mobility or to alter the mobility of the displacing fluids (Speight,
2009). In some cases, the effects of gravity forces, which ordinarily cause vertical segregation of fluids of different densities, can be
minimized or even used to advantage. The various processes differ considerably in complexity, the physical mechanisms responsible for oil recovery, and the amount of experience that has been
derived from field application. The degree to which the enhanced
oil recovery methods are applicable in the future will depend on
development of improved process technology. It will also depend
on improved understanding of fluid chemistry, phase behavior,
and physical properties; and on the accuracy of geology and reservoir engineering in characterizing the physical nature of individual
reservoirs (Borchardt and Yen, 1989).
Thermal methods for oil recovery have found most use when the
oil in the reservoir has a high viscosity. For example, heavy oil is
usually highly viscous with a viscosity ranging from approximately
In these reservoirs it is desirable to initiate enhanced oil recovery (EOR) operations as early as possible. This may mean considerably abbreviating conventional secondary recovery operations or
bypassing them altogether. Thermal floods using steam and controlled in situ combustion methods are also used. Thermal methods of recovery reduce the viscosity of the crude oil by heat so that
it flows more easily into the production well. Thus tertiary techniques are usually variations of secondary methods with a goal of
improving the sweeping action of the invading fluid.
Enhanced oil recovery methods are designed to reduce the viscosity of the crude oil (i.e. to reduce the pour point of the crude oil
relative to the temperature of the reservoir), thereby increasing oil
production. Enhanced oil recovery methods are applied started
when secondary oil recovery techniques are no longer enough to
sustain production. The oil remaining after conventional recovery
operations is retained in the pore space of reservoir rock at a lower
concentration than originally existed. In portions of the reservoir that
have been contacted or swept by the injection fluid, the residual oil
remains as droplets (or ganglia) trapped in either individual pores or
clusters of pores. It may also remain as films partly coating the pore
walls. Entrapment of this residual oil is predominantly due to capillary and surface forces and to geometry of the pore systems.
Enhanced oil recovery processes use thermal, chemical, or fluid
phase behavior effects to reduce or eliminate the capillary forces
that trap oil within pores, to thin the oil or otherwise improve its
mobility or to alter the mobility of the displacing fluids (Speight,
2009). In some cases, the effects of gravity forces, which ordinarily cause vertical segregation of fluids of different densities, can be
minimized or even used to advantage. The various processes differ considerably in complexity, the physical mechanisms responsible for oil recovery, and the amount of experience that has been
derived from field application. The degree to which the enhanced
oil recovery methods are applicable in the future will depend on
development of improved process technology. It will also depend
on improved understanding of fluid chemistry, phase behavior,
and physical properties; and on the accuracy of geology and reservoir engineering in characterizing the physical nature of individual
reservoirs (Borchardt and Yen, 1989).
Thermal methods for oil recovery have found most use when the
oil in the reservoir has a high viscosity. For example, heavy oil is
usually highly viscous with a viscosity ranging from approximately