76 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
accumulations and the existence of wide ranges of both rock and
fluid properties, reservoirs respond differently and must be treated
individually. The size, shape, and degree of interconnection of the
pores vary considerably from place to place in an individual reservoir. Below the oil layer, the sandstone is usually saturated with
salt water. The oil is released from this formation by drilling a well
and puncturing the limestone layer on either side of the limestone
dome or fold. If the peak of the formation is tapped, only the gas
is obtained. If the penetration is made too far from the center, only
salt water is obtained.
Over the lifetime of the well the pressure will fall, and at some
point there will be insufficient underground pressure to force the
oil to the surface. Secondary oil recovery uses various techniques
to aid in recovering oil from depleted or low-pressure reservoirs.
Sometimes pumps, such as beam pumps (horse head pumps) and
electrical submersible pumps are used to bring the oil to the surface.
Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas re-injection, and gas lift which
injects air, carbon dioxide or some other gas into the reservoir.
Enhanced oil recovery (tertiary oil recovery, EOR) relies on methods that reduce the viscosity of the oil to increase (Speight, 2009).
Tertiary recovery is started when secondary oil recovery techniques are no longer enough to sustain production. For example,
thermally-enhanced oil recovery methods are recovery methods in
which the oil is heated the oil and make it easier to extract; usually
steam is used for heating the oil.
Conventional primary and secondary recovery processes are
ultimately expected to produce about one-third of the original oil
discovered, although recovery (which is reservoir and oil dependent) from individual reservoirs can range from less than 5% to as
high as 80% of the original oil in place. This broad range of recovery efficiency is a result of variations in the properties of the specific rock and fluids involved from reservoir to reservoir as well as
the kind and level of energy that drives the oil to producing wells,
where it is captured.
Conventional oil production methods may be unsuccessful
because the management of the reservoir was poor or because reservoir heterogeneity has prevented the recovery of crude oil in an
economical manner. Reservoir heterogeneity, such as fractures and
faults, can cause reservoirs to drain inefficiently by conventional
methods. Also, highly cemented or shale zones can produce barriers
accumulations and the existence of wide ranges of both rock and
fluid properties, reservoirs respond differently and must be treated
individually. The size, shape, and degree of interconnection of the
pores vary considerably from place to place in an individual reservoir. Below the oil layer, the sandstone is usually saturated with
salt water. The oil is released from this formation by drilling a well
and puncturing the limestone layer on either side of the limestone
dome or fold. If the peak of the formation is tapped, only the gas
is obtained. If the penetration is made too far from the center, only
salt water is obtained.
Over the lifetime of the well the pressure will fall, and at some
point there will be insufficient underground pressure to force the
oil to the surface. Secondary oil recovery uses various techniques
to aid in recovering oil from depleted or low-pressure reservoirs.
Sometimes pumps, such as beam pumps (horse head pumps) and
electrical submersible pumps are used to bring the oil to the surface.
Other secondary recovery techniques increase the reservoir's pressure by water injection, natural gas re-injection, and gas lift which
injects air, carbon dioxide or some other gas into the reservoir.
Enhanced oil recovery (tertiary oil recovery, EOR) relies on methods that reduce the viscosity of the oil to increase (Speight, 2009).
Tertiary recovery is started when secondary oil recovery techniques are no longer enough to sustain production. For example,
thermally-enhanced oil recovery methods are recovery methods in
which the oil is heated the oil and make it easier to extract; usually
steam is used for heating the oil.
Conventional primary and secondary recovery processes are
ultimately expected to produce about one-third of the original oil
discovered, although recovery (which is reservoir and oil dependent) from individual reservoirs can range from less than 5% to as
high as 80% of the original oil in place. This broad range of recovery efficiency is a result of variations in the properties of the specific rock and fluids involved from reservoir to reservoir as well as
the kind and level of energy that drives the oil to producing wells,
where it is captured.
Conventional oil production methods may be unsuccessful
because the management of the reservoir was poor or because reservoir heterogeneity has prevented the recovery of crude oil in an
economical manner. Reservoir heterogeneity, such as fractures and
faults, can cause reservoirs to drain inefficiently by conventional
methods. Also, highly cemented or shale zones can produce barriers