The United States may not have as much economically viable underground CO2 storage space as previously thought

A new model to predict the economic viability of CO2 geosequestration in sandstone saline aquifers indicates that previous estimates for storage potential in the U. S. may be overly optimistic (Eccles et al., 2009).  The model identifies an estimated minima for storage costs in a typical basin in the range of $2–7 per ton CO2 sequestered, based on estimates of a maximum CO2 storage potential and a maximum CO2 injection rate.    Eccles et al. use data from carbon capture and storage pilot projects to explain that many assumptions in their model lead to artificially high estimates for the maximum storage potential and the maximum injection rate, and as a result, they conclude that geosequestration will be even more expensive than their model conservatively indicates. However, Eccles et al. proceed to apply the model to identifying economically optimal storage basins in the United States.— Shanna Hoversten
 
Eccles, J., Pratson, L., Newell, R., Jackson, R., 2009. Physical and Economic Potential of Geological CO2 Storage in Saline Aquifers. Environmental Science & Technology 43, 1962–1969.

 

J. K. Eccles and colleagues at the Nicholas School of the Environment, Duke University, begin building their model by estimating maximum storage potential as a function of the optimal injection depth and the available void space in the formation.  However, this estimate does not account for the reality of most pilot projects, during which the CO2 has bypassed the majority of the available pore space.  The maximum injection rate is calculated based on a determination of the injection-induced pressure that would cause hydraulic fracturing beyond the perforated zone around the well. However, comparison of the modelled results with the pilot project at Nagaoka, Japan indicates that lower injection rates are probably more realistic due to engineering constraints and actual reservoir conditions.  The cost per ton of CO2 sequestered is generated based on the total cost of drilling, injection, equipment, and operation and maintenance, notably excluding the costs that would arise from capture and transport of the CO2.  Finally, the cost for storage in a typical basin in the United States was computed using estimates for storage potential and the cost per ton of CO2 stored. 

Results from the modelling indicate that although depth is an important determinant of storage potential, it is not the most important factor in storage cost.  While increased depth can increase the cost by a factor of two, layer thickness and permeability of the storage reservoir can increase cost by a factor of fifty.  This hints at the myriad of basin characteristics that need to be assessed before arriving at a viable cost estimate.  Additionally, costs within a single basin are likely to differ considerably due to the extreme variability in aquifer characteristics.  The most important conclusion that can be drawn from this analysis is that the amount of CO2 storage provided by low-cost regions within saline aquifers in the United States is considerably lower than the estimates reported by previous studies.  The study by Eccles et al. suggests that there are only perhaps ten storage reservoirs in the United States that would have an average storage cost of below $10 per ton CO2.  If more basins are to become economically viable for CO2 storage, then policymakers will need to devise a regime that imposes a rather significant cost on carbon.—Shanna Hoversten

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