82 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
similar to that used for water injection can be used (dispersed gas
injection). Thus, dispersed gas injection is anticipated to be more
effective in reservoirs that are relatively thin and have little dip.
Injection into the top of the formation or into the gas cap is more
successful in reservoirs with higher vertical permeability (200 md
or more) and enough vertical relief to allow the gas cap to displace
the oil downward.
During the withdrawal of fluids from a well, it is usual practice
to maintain pressures in the reservoir at or near the original levels
by pumping either gas or water into the reservoir as the hydrocarbons are withdrawn. This practice has the advantage of retarding
the decline in the production of individual wells and considerably
increasing the ultimate yield. It also may bring about the conservation of gas that otherwise would be wasted, and the disposal of
brines that otherwise might pollute surface and near-surface potable waters.
Water injection is still predominantly a secondary recovery process — waterflood. Probably the principal reason for this is that
reservoir formation water is ordinarily not available in volume during the early years of an oil field and pressure maintenance water
from outside the field may be too expensive. When a young field
produces considerable water, it may be injected back into the reservoir primarily for the purpose of nuisance abatement, but reservoir
pressure maintenance is a valuable by-product.
Nevertheless, some passages in the formation are larger than
others, and the water tends to flow freely through these, bypassing
smaller passages where the oil remains. A partial solution to this
problem is possible by miscible fluid flooding. Liquid butane and
propane are pumped into the ground under considerable pressure,
dissolving the oil and carrying it out of the smaller passages; additional pressure is obtained by using natural gas.
3.3.3 Enhanced Oil Recovery
Enhanced oil recovery (tertiary oil recovery) is the incremental
ultimate oil that can be recovered from a petroleum reservoir over
oil that can be obtained by primary and secondary recovery methods (Speight, 2009). In fact, certain reservoir types, such as those
with very viscous crude oils and some low-permeability carbonate
(limestone, dolomite, or chert) reservoirs, respond poorly to conventional secondary recovery techniques.
similar to that used for water injection can be used (dispersed gas
injection). Thus, dispersed gas injection is anticipated to be more
effective in reservoirs that are relatively thin and have little dip.
Injection into the top of the formation or into the gas cap is more
successful in reservoirs with higher vertical permeability (200 md
or more) and enough vertical relief to allow the gas cap to displace
the oil downward.
During the withdrawal of fluids from a well, it is usual practice
to maintain pressures in the reservoir at or near the original levels
by pumping either gas or water into the reservoir as the hydrocarbons are withdrawn. This practice has the advantage of retarding
the decline in the production of individual wells and considerably
increasing the ultimate yield. It also may bring about the conservation of gas that otherwise would be wasted, and the disposal of
brines that otherwise might pollute surface and near-surface potable waters.
Water injection is still predominantly a secondary recovery process — waterflood. Probably the principal reason for this is that
reservoir formation water is ordinarily not available in volume during the early years of an oil field and pressure maintenance water
from outside the field may be too expensive. When a young field
produces considerable water, it may be injected back into the reservoir primarily for the purpose of nuisance abatement, but reservoir
pressure maintenance is a valuable by-product.
Nevertheless, some passages in the formation are larger than
others, and the water tends to flow freely through these, bypassing
smaller passages where the oil remains. A partial solution to this
problem is possible by miscible fluid flooding. Liquid butane and
propane are pumped into the ground under considerable pressure,
dissolving the oil and carrying it out of the smaller passages; additional pressure is obtained by using natural gas.
3.3.3 Enhanced Oil Recovery
Enhanced oil recovery (tertiary oil recovery) is the incremental
ultimate oil that can be recovered from a petroleum reservoir over
oil that can be obtained by primary and secondary recovery methods (Speight, 2009). In fact, certain reservoir types, such as those
with very viscous crude oils and some low-permeability carbonate
(limestone, dolomite, or chert) reservoirs, respond poorly to conventional secondary recovery techniques.