Reservoirs carbon dioxide storage

The idea here is to capture carbon dioxide from power plants and then inject it into natural gas hydrate reservoirs assumed to contain primarily methane hydrate. Thus one achieves the simultaneous sequestration of carbon dioxide with the production of natural gas. Lee et al. (2003) presented laboratory data that showed the replacement of methane molecules by C02. Yoon et al. (2004) and Ota et al. (2005) confirmed these laboratory findings. Park et al. (2006a) used a CO2/N2 mixture containing 20 mol % carbon dioxide (flue gas) instead of pure C02 and noticed that the methane recoveiy increased from 64 to 85 %. A similar idea for sequestering captured C02 is to use it as cushion gas for natural gas storage in reservoirs (Oldenburg, 2003). 

Another way to increase Earth s ability to store carbon is by creating new, artificial carbon sinks that would trap excess carbon gas produced by human activity before it enters the atmosphere. The carbon dioxide would be collected and placed in a new location for controllable, long-term storage. Scientists have already experimented with two new carbon sink locations, one deep in the ocean, the other underground. In each case, carbon is forcefully injected into its new reservoir for long-term storage. 

Another means to reduce man-made carbon dioxide emissions is sequestration in the land or the ocean. When carbon dioxide is produced locally it may be possible to efficiently separate it from other gases, concentrate it, and dispose of it. A number of complex scenarios may be envisioned to accomplish this disposal, from pumping it into the ocean, to displacing methane in coal mines, to storage in depleted hydrocarbon reservoirs. 

Studies have shown that the storage of carbon dioxide is possible in various geological settings. The main candidates are sedimentary basins, e.g., oil and gas reservoirs (working or abandoned), deep unmineable coal-seams and saline formations (aquifers). Sub-surface storage can take place at both on-shore and off-shore locations access to the latter is via pipelines from the shore or from off-shore platforms. Other prospective sites for storage include salt caverns, basalts, oil/gas shales and disused mines. The various options are shown schematically in Figure 3.4. 

Figure 3.4 Options for the geological storage of carbon dioxide. 1. Deep unused saline formations (aquifers). 2. Use of carbon dioxide for enhanced oil recovery. 3. Depleted oil and gas reservoirs. 4. Deep unmineable coal seams. 5. Use of carbon dioxide in enhanced coal-bed methane recovery. 6. Other suggested options (e.g., salt caverns, basalts, oil/gas shales, disused mines)." (Courtesy of Intergovernmental Panel on Climate Change).

Residual storage Reservoir rocks act like a tight, rigid sponge. Air in a sponge is residually tr ped and the sponge usually has to be squeezed several times to replace the air with water. When Uquid carbon dioxide is pumped into a rock formation, much of it becomes smck within the pore spaces of the rock and does not move. 

Of these, oil and gas reservoirs are the most attractive. Active oil wells can utilize the carbon dioxide in tertiary recovery, and CO2 can be used as a sweep gas to promote the production of methane from certain types of coal deposits. Furthermore, because these geological formations have already demonstrated their ability to hold oil and gas, there are no obvious environmental consequences to long-term storage in such locations. The same cannot be said for deep oceans and deep saline geological formations. Those sites, although promising, hold potential uncertainties in retention and environmental impacts. 

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