Risks and Benefits of Geologic Sequestration of Carbon Dioxide - How Do the Pieces Fit Together?

I. Duncan
Bureau of Economic Geology, University of Texas, Austin, TX, [email protected]

Geologic sequestration of CO₂ as part of the carbon capture and storage (CCS) process has proven potential to provide significant reductions in atmospheric emissions. In CCS, CO₂ will be captured from fossil fuel power plants, compressed, transported by pipeline and injected into deep brine reservoirs or utilized in CO₂-based enhanced oil recovery (EOR). The benefit of CO₂ EOR to the economy could be significant in a carbon-constrained world; however, as in any other major industrial process there are risks to human health and safety and to the environment.

Operational risks include: leakage from CO₂ pipelines; blowouts of injection wells; and blowouts of poorly plugged, abandoned wells that may intersect the CO₂ plume. The 37-year safety record of the CO₂-EOR industry is the most tangible record that we have to estimate the operational risks of CO₂ sequestration. A detailed understanding of this record, and of the differences between operational requirements of CO₂-EOR and future sequestration projects, is required to make quantitative inferences of future societal risk. Techniques to ensure that a sequestration site will retain CO₂ for sufficient time periods to achieve the desired benefits for the atmosphere and to avoid environmental problems include careful site characterization, modeling, and monitoring. Risks from leakage of the natural containment system (typically a shale seal) include possible contamination of drinking water, impact on ecosystems, return to the atmosphere, and economic damage to mineral resources (in particular, gas reservoirs).

Insights gained from CO₂-EOR projects, natural CO₂ leakage in volcanic terrains, and pilot brine injection projects suggest that the potential damages in most cases are very limited and that risks can be substantially reduced by selecting high-quality sites. Appropriate monitoring together with strategic early mitigation may significantly lower the risk of long-term environmental damages.

CO₂ EOR is proposed as a valuable first step, followed by even larger volume sequestration in deeper brine reservoirs.

AAPG Search and Discovery Article #90088©2009 Pacific Section Meeting, Ventura, California, May 3-5, 2009