EXPLORATION, RECOVERY, AND TRANSPORTATION 75
fracturing the rock. The grains of sand remain, helping to hold the
cracks open.
Thus, once the well is completed, the flow of oil into the well is
commenced. For limestone reservoir rock, acid is pumped down
the well and out the perforations. The acid dissolves channels in
the limestone that lead oil into the well. For sandstone reservoir
rock, a specially blended fluid containing proppants (sand, walnut
shells, aluminum pellets) is pumped down the well and out the
perforations. The pressure from this fluid makes small fractures in
the sandstone that allow oil to flow into the well, while the proppants hold these fractures open. Once the oil is flowing, the oil rig
is removed from the site and production equipment is set up to
extract the oil from the well.
3.3 Recovery
Recovery, as applied in the petroleum industry, is the production of
oil from a reservoir. There are several methods by which this can be
achieved that range from recovery due to reservoir energy (i.e. the oil
flows from the well hole without assistance) to enhanced recovery
methods in which considerable energy must be added to the reservoir to produce the oil. However, the effect of the method on the oil
and on the reservoir must be considered before application.
Generally, crude oil reservoirs exist with an overlying gas cap,
in communication with aquifers, or both. The oil resides together
with water and free gas in very small holes and fractures. If the
underground pressure in the oil reservoir is sufficient, the oil will
be forced to the surface under this pressure (primary recovery).
Natural gas (associated natural gas) is often present, which also
supplies needed underground pressure (primary recovery). In
this situation it is sufficient to place an arrangement of valves (the
Christmas tree) on the wellhead to connect the well to a pipeline
network for storage and processing. The crude oil is typically collected from individual wells by small pipelines.
In some cases this pressure later diminishes so that the oil must
be pumped from the well. Natural gas or water is sometimes
pumped into the well to replace the oil that is withdrawn - this is
often referred to as repressurizing the oil well.
The anatomy of a reservoir is complex and is site specific, microscopically and macroscopically. Because of the various types of
fracturing the rock. The grains of sand remain, helping to hold the
cracks open.
Thus, once the well is completed, the flow of oil into the well is
commenced. For limestone reservoir rock, acid is pumped down
the well and out the perforations. The acid dissolves channels in
the limestone that lead oil into the well. For sandstone reservoir
rock, a specially blended fluid containing proppants (sand, walnut
shells, aluminum pellets) is pumped down the well and out the
perforations. The pressure from this fluid makes small fractures in
the sandstone that allow oil to flow into the well, while the proppants hold these fractures open. Once the oil is flowing, the oil rig
is removed from the site and production equipment is set up to
extract the oil from the well.
3.3 Recovery
Recovery, as applied in the petroleum industry, is the production of
oil from a reservoir. There are several methods by which this can be
achieved that range from recovery due to reservoir energy (i.e. the oil
flows from the well hole without assistance) to enhanced recovery
methods in which considerable energy must be added to the reservoir to produce the oil. However, the effect of the method on the oil
and on the reservoir must be considered before application.
Generally, crude oil reservoirs exist with an overlying gas cap,
in communication with aquifers, or both. The oil resides together
with water and free gas in very small holes and fractures. If the
underground pressure in the oil reservoir is sufficient, the oil will
be forced to the surface under this pressure (primary recovery).
Natural gas (associated natural gas) is often present, which also
supplies needed underground pressure (primary recovery). In
this situation it is sufficient to place an arrangement of valves (the
Christmas tree) on the wellhead to connect the well to a pipeline
network for storage and processing. The crude oil is typically collected from individual wells by small pipelines.
In some cases this pressure later diminishes so that the oil must
be pumped from the well. Natural gas or water is sometimes
pumped into the well to replace the oil that is withdrawn - this is
often referred to as repressurizing the oil well.
The anatomy of a reservoir is complex and is site specific, microscopically and macroscopically. Because of the various types of