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CO
2
Sequestration in Hydrocarbon Reservoirs
Mark
H. Holtz and Robert
J. Finley
Emissions
of industrial greenhouse gases have increased the total load of carbon
in the atmosphere. Although the long-term consequences of these emissions
are hotly debated, one possible outcome is the alteration of global climate
as greenhouse gases trap heat at the Earth's surface. The electricity-generation
industry is currently a major source of atmospheric CO
2
emissions, and one industry challenge in the coming decades may be to
profitably employ advanced technology that reduces CO
2
output while maintaining generation availability and reliability. There
are likely to be many different strategies applied to new generation additions,
but the viable alternatives for existing facilities are relatively limited.
Capture and sequestration of CO
2
in mature
oil reservoirs appear to be one important management alternative for the
existing generating unit. The likelihood that CO
2
disposal in hydrocarbon reservoirs will become economically feasible is
greatly increased if the disposal process provides readily quantifiable
ancillary benefits, such as enhanced oil recovery (EOR) though CO
2
injection. Whereas the benefits of reducing CO
2
emissions are long term, global, and potentially difficult to quantify,
the benefits of enhanced oil recovery are immediate and quantifiable.
The proximity of large power plants to oil and gas reservoirs, many of
them nearing their apparent economic limit, makes Texas the logical geographic
area to test the feasibility of this method of greenhouse-gas sequestration
in the United States. Funded by the Electric Power Research Institute,
this preliminary Bureau investigation evaluated the suitability of Texas
reservoirs for sequestering CO
2
produced by
major power plants. Preliminary analyses indicate that CO
2
capture for lignite- and coal-fired plants in Texas may be cost effective
when compared with fuel-switching these same boilers to natural gas. From
a policy standpoint, it may be desirable to encourage CO
2
capture retrofit initially, as opposed to fuel switching, to achieve overall
lower levels of CO
2
emissions at a comparable
cost. Previous research indicated that a primary target for EOR in Texas
is estimated at 74 billion stock-tank barrels (BSTB) of residual oil.
This study finds that 8 BSTB of this resource is within a 90-mi (145-km)
radius of the candidate coal- or lignite-fired plants in Texas. Additional
oil resources beyond this 8 BSTB are also available from oil fields located
near natural-gas-fired facilities, but additional CO
2
-effluent-management
issues need to be addressed with these facilities. Factors influencing
the recovery of these resources include CO
2
production cost and availability, generation-unit characteristics, transportation
cost, environmental regulations, and oil prices. Modeling conducted in
this study indicates that CO
2
flooding can
produce oil that would not otherwise be recovered, at an incremental cost
between $6 and $16 per stock-tank barrel. In addition, it is likely that
between 12 and 20 years of CO
2
production from
the candidate lignite- or coal-fired boilers can be sequestered from these
generation facilities. Therefore, we conclude that there is substantial
potential for using utility plant boiler effluent as a CO
2
supply source for flooding and using mature oil reservoirs for CO
2
sequestration. Development of this potential resource base may be facilitated
through further research and policy initiatives.
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