Geoscience Reference
In-Depth Information
Oil and Gas Reservoirs
Pumping CO
2
into oil and gas reservoirs to boost production (EOR) is
practiced in the petroleum industry today. The United States is a world leader
in this technology, and oil and gas operators inject approximately 48 MtCO
2
underground each year to help recover oil and gas resources.
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Most of the CO
2
used for EOR in the United States comes from naturally occurring geologic
formations, however, not from industrial sources. Using CO
2
from industrial
emitters has appeal because the costs of capture and transport from the facility
could be partially offset by revenues from oil and gas production.
Carbon dioxide can be used for EOR onshore or offshore. To date, most
CO
2
projects associated with EOR are onshore, with the bulk of U.S. activities
in west Texas. Carbon dioxide can also be injected into oil and gas reservoirs
that are completely depleted, which would serve the purpose of long-term
sequestration, but without any offsetting benefit from oil and gas production.
Advantages and Disadvantages
Depleted or abandoned oil and gas fields, especially in the United States,
are considered prime candidates for CO
2
storage for several reasons:
oil and gas originally trapped did not escape for millions of years,
demonstrating the structural integrity of the reservoir;
extensive studies for oil and gas typically have characterized the
geology of the reservoir;
computer models have often been developed to understand how
hydrocarbons move in the reservoir, and the models could be applied
to predicting how CO
2
could move; and
infrastructure and wells from oil and gas extraction may be in place
and might be used for handling CO
2
storage.
Some of these features could also be disadvantages to CO
2
sequestration.
Wells that penetrate from the surface to the reservoir could be conduits for
CO
2
release if they are not plugged properly. Care must be taken not to
overpressure the reservoir during CO
2
injection, which could fracture the
caprock—the part of the formation that formed a seal to trap oil and gas—and
subsequently allow CO
2
to escape. Also, shallow oil and gas fields (those less
than 800 meters deep, for example) may be unsuitable because CO
2
may form
a gas instead of a denser liquid and could escape to the surface more easily. In
addition, oil and gas fields that are suitable for EOR may not necessarily be
