220.127.116.11.2 Transmission and Storage of CO2
CO2 can be transported to storage sites using high-pressure pipelines
or by ship. Pipelines are used routinely today to transport CO2 long
distances for use in enhanced oil recovery (Stevens et al., 2000). Although
CO2 is not transported by ship at present, tankers similar to those
currently used for liquefied petroleum gas (LPG) could be used for this purpose
CO2 exists in natural underground reservoirs in various parts of
the world. Potential sites for storage of captured CO2 are underground
reservoirs, such as depleted oil and gas fields or deep saline reservoirs. CO2
injected into coal beds may be preferentially absorbed, displacing methane from
the coal; sequestration would be achieved providing the coal is never mined.
Another possible storage location for captured CO2 is the deep ocean,
but this option is at an earlier stage of development than underground reservoirs;
so far only small-scale experiments for preliminary investigation have been
carried out (Herzog et al., 2000); the deep ocean is chemically able
to dissolve up to 1800GtC (Sato, 1999). An indication of the global capacities
of the major storage options is given in Table 3.34. The
capacities of these reservoirs are subject to substantial uncertainty, as purposeful
exploration has only been conducted in some parts of the world so far. Other
published estimates of the global capacity for storage in underground aquifers
range up to 14,000GtC (Hendriks, 1994). Other methods of CO2 storage
have been suggested but none are competitive with underground storage (Freund,
Substantial amounts of CO2 are already being stored in underground
- Nearly 1Mt/yr of CO2 is being stored in a deep saline reservoir
about 800m beneath the bed of the North Sea as part of the Sleipner Vest gas
production project (Baklid and Korbol, 1996). This is the first time CO2
has been stored purely for reasons of climate protection.
- About 33Mt/yr of CO2 is used at more than 74 enhanced oil recovery
(EOR) projects in the USA. Most of this CO2 is extracted from natural
CO2 reservoirs but some is captured from gas processing plants.
Much of this CO2 remains in the reservoir at the completion of
oil production; any CO2 produced with the oil is separated and
reinjected. An example of an EOR scheme which will use anthropogenic CO2
is the Weyburn project in Canada (Wilson et al., 2000). In this project,
5,000 t/d of CO2 captured in a coal gasification plant in North
Dakota, USA will be piped to the Weyburn field in Saskatchewan, Canada.
- At the Allison unit in New Mexico, USA, (Stevens et al., 1999),
over 100,000 tonnes of CO2 has been injected over a three-year
period to enhance production of coal bed methane. The injected CO2
is sequestered in the coal (providing it is never mined). This is the first
example of CO2-enhanced coal bed methane production.
The cost of CO2 transport and storage depends greatly on the transport
distance and the capacity of the pipeline. The cost of transporting large quantities
of CO2 is approximately US$1-3/t per 100km (Ormerod, 1994; Doctor
et al., 2000). The cost of underground storage, excluding compression
and transport, would be approximately US$1-2/tCO2 stored (Ormerod,
1994). The overall cost of transport and storage for a transport distance of
300 km would therefore be about US$8/tCO2 stored, equivalent to about
US$10/t of emissions avoided (US$37/tC).
If the CO2 is used for enhanced oil recovery (EOR) or enhanced coal
bed methane production (ECBM), there is a valuable product (oil or methane,
respectively) which would help to offset the cost of CO2 capture
and transport. In some EOR or ECBM projects, the net cost of CO2
capture and storage might be negative. Other ideas for utilizing CO2
to make valuable products have not proved to be as useful as sequestration measures,
because of the amount of energy consumed in the process and the relatively insignificant
quantities of CO2 which would be used.
If no valuable products were produced, the overall cost of CO2 capture
and storage would be about US$40-60/t CO2 emissions avoided (150-220/tC).
As with most new technologies, there is scope to reduce these costs in the future
through technical developments and wider application.