Changes

==Risks==

==Risks==

[[Risk: expected value and chance of success|Risks]] surrounding CO₂ geosequestration are summarized by Bowden and Rigg.<ref name=Bowdenandrigg_2004>Bowden, A. R., and A. J. Rigg, 2004, Assessing risk in CO₂ storage projects: The Australian Petroleum Production and Exploration Association (APPEA) Journal, v. 44, no. 1, p. 677–702.</ref> Essentially, the main concerns relate to the potential for unanticipated CO₂ leakage either caused by unanticipated CO₂ movement up the wellbore or along an unexpected geological migration path or caused by induced or natural [[seismicity]]. The risks associated with CO₂ storage, although considered very low, are characterized by a greater degree of uncertainty than those connected with CO₂ transport and injection. This is because of the fact that once the CO2 enters the geological reservoir, its fate is transferred from mostly human control to a natural system. Although most of the existing knowledge of CO₂ behavior in the subsurface exists from the long history of CO₂ floods associated with [[Enhanced oil recovery|EOR]], the risks associated with large-scale storage are at a different scale. The quantities of CO₂ stored for EOR floods are smaller, and the CO₂ residence times are shorter than required for large-scale carbon [[Carbon dioxide (CO2) sequestration|geosequestration]]. For geosequestration of CO₂, the risk of leakage depends on not only the likelihood of existence of potential leakage pathways (such as wells, [[fault]]s, permeable zones in the [[seal]], etc.), but also the likelihood that these potential pathways will intersect CO₂ while it is in a mobile phase and finally the likelihood that the potential leakage pathway will leak.<ref name=Riggetal_2006>Rigg, A., A. Bowden, M. N. Watson, 2006, Risk assessment of long-term containment of CO2 in geological storage projects: Abstracts volume, AAPG International Conference and Exhibition, November 5–8, 2006, Perth, Australia, v. 16, p. 117.</ref> As many containment risk assessments are benchmarked against an impact of 1% leakage over 1000 years,<ref name=IPCC_2005 /> the frequency, duration, and volume of potential leakage events need to be assessed for this time frame.<ref name=Riggetal_2006 />

[[Risk: expected value and chance of success|Risks]] surrounding CO₂ geosequestration are summarized by Bowden and Rigg.<ref name=Bowdenandrigg_2004>Bowden, A. R., and A. J. Rigg, 2004, Assessing risk in CO₂ storage projects: The Australian Petroleum Production and Exploration Association (APPEA) Journal, v. 44, no. 1, p. 677–702.</ref> Essentially, the main concerns relate to the potential for unanticipated CO₂ leakage either caused by unanticipated CO₂ movement up the wellbore or along an unexpected geological migration path or caused by induced or natural [http://earthquake.usgs.gov/learn/glossary/?term=seismicity seismicity]. The risks associated with CO₂ storage, although considered very low, are characterized by a greater degree of uncertainty than those connected with CO₂ transport and injection. This is because of the fact that once the CO2 enters the geological reservoir, its fate is transferred from mostly human control to a natural system. Although most of the existing knowledge of CO₂ behavior in the subsurface exists from the long history of CO₂ floods associated with [[Enhanced oil recovery|EOR]], the risks associated with large-scale storage are at a different scale. The quantities of CO₂ stored for EOR floods are smaller, and the CO₂ residence times are shorter than required for large-scale carbon [[Carbon dioxide (CO2) sequestration|geosequestration]]. For geosequestration of CO₂, the risk of leakage depends on not only the likelihood of existence of potential leakage pathways (such as wells, [[fault]]s, permeable zones in the [[seal]], etc.), but also the likelihood that these potential pathways will intersect CO₂ while it is in a mobile phase and finally the likelihood that the potential leakage pathway will leak.<ref name=Riggetal_2006>Rigg, A., A. Bowden, M. N. Watson, 2006, Risk assessment of long-term containment of CO2 in geological storage projects: Abstracts volume, AAPG International Conference and Exhibition, November 5–8, 2006, Perth, Australia, v. 16, p. 117.</ref> As many containment risk assessments are benchmarked against an impact of 1% leakage over 1000 years,<ref name=IPCC_2005 /> the frequency, duration, and volume of potential leakage events need to be assessed for this time frame.<ref name=Riggetal_2006 />

Any geological CO₂ storage project resulting in a catastrophic release of CO₂ is highly unlikely. This is because the pressure of CO₂ injected into a geological [[reservoir]] reduces as it moves away from the injection well and is diffused over large areas of the formation, thus avoiding large pressure buildups.<ref name=Streitandhillis_2002>Streit, J. E., and R. R. Hillis, 2002, [https://www.onepetro.org/conference-paper/SPE-78226-MS Estimating fluid pressures that can induce reservoir failure during hydrocarbon depletion]: Society of Petroleum Engineers/International Society for Rock Mechanics (ISRM) Rock Mechanics Conference, October 2002, Irving, Texas, SPE Paper No. 78226, 7 p.</ref> No record of a catastrophic CO₂ release from a natural CO₂ deposit to date (2009) is observed, and any potential release from a CO₂ storage project should be preventable through careful site selection, operation, and monitoring. The critical geological input to minimize the risk of such occurrence is seal analysis and [[geomechanics]]. The CO₂ column height calculations can be used to assess the safe storage volumes of CO₂ at any storage site,<ref name=Danielandkaldi_2009>Daniel, R. F., and J. G. Kaldi, 2009, [http://archives.datapages.com/data/specpubs/study59/CHAPTER18/CHAPTER18.HTM Evaluating seal capacity of cap rocks and intraformational barriers for CO₂ containment], in M. Grobe, J. C. Pashin, and R. L. Dodge, eds., Carbon dioxide sequestration in geological media—State of the science: [http://store.aapg.org/detail.aspx?id=739 AAPG Studies in Geology 59], p. 335–345.</ref> whereas geomechanical analysis of the faults can be used to assess the maximum sustainable pore fluid pressures at potential storage sites (Streit and Hillis, 2004). Understanding the rock fluid interaction potential between CO₂ and contacted minerals is also important. The CO₂ creates [http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=767 carbonic acid] when it mixes with H₂O, and the risk of whether this could potentially result in the chemical erosion of some seal lithologies leading to leakage needs to be addressed. In most instances, because of their low [[permeability]] and [[Capillary pressure|capillary properties]], CO₂ is unlikely to enter seals. Therefore, any potential reactions are likely to be limited to the base of the seal. In addition, because the [http://chemistry.about.com/od/chemistryglossary/a/phdef.htm pH] buffering capabilities of the seal lithology are generally greater than the dissolution capabilities of carbonic acid, reactions are likely to be mineral precipitation instead of dissolution, thus leading to seal capacity enhancement instead of degradation.<ref name=Watsonetal_2005>Watson, M. N., R. F. Daniel, P. R. Tingate, and C. M. Gibson-Poole, 2005, CO₂-related seal capacity enhancement in mudstones: Evidence from the pine lodge natural CO₂ accumulation, Otway Basin, Australia, in M. Wilson, T. Morris, J. Gale, and K. Thambimuthu, eds., Greenhouse gas control technologies: Proceedings of the 7th International Conference on Greenhouse Gas Control Technologies: Oxford, Elsevier, v. 2, part 2, p. 2313–2316.</ref>

Any geological CO₂ storage project resulting in a catastrophic release of CO₂ is highly unlikely. This is because the pressure of CO₂ injected into a geological [[reservoir]] reduces as it moves away from the injection well and is diffused over large areas of the formation, thus avoiding large pressure buildups.<ref name=Streitandhillis_2002>Streit, J. E., and R. R. Hillis, 2002, [https://www.onepetro.org/conference-paper/SPE-78226-MS Estimating fluid pressures that can induce reservoir failure during hydrocarbon depletion]: Society of Petroleum Engineers/International Society for Rock Mechanics (ISRM) Rock Mechanics Conference, October 2002, Irving, Texas, SPE Paper No. 78226, 7 p.</ref> No record of a catastrophic CO₂ release from a natural CO₂ deposit to date (2009) is observed, and any potential release from a CO₂ storage project should be preventable through careful site selection, operation, and monitoring. The critical geological input to minimize the risk of such occurrence is seal analysis and [[geomechanics]]. The CO₂ column height calculations can be used to assess the safe storage volumes of CO₂ at any storage site,<ref name=Danielandkaldi_2009>Daniel, R. F., and J. G. Kaldi, 2009, [http://archives.datapages.com/data/specpubs/study59/CHAPTER18/CHAPTER18.HTM Evaluating seal capacity of cap rocks and intraformational barriers for CO₂ containment], in M. Grobe, J. C. Pashin, and R. L. Dodge, eds., Carbon dioxide sequestration in geological media—State of the science: [http://store.aapg.org/detail.aspx?id=739 AAPG Studies in Geology 59], p. 335–345.</ref> whereas geomechanical analysis of the faults can be used to assess the maximum sustainable pore fluid pressures at potential storage sites (Streit and Hillis, 2004). Understanding the rock fluid interaction potential between CO₂ and contacted minerals is also important. The CO₂ creates [http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=767 carbonic acid] when it mixes with H₂O, and the risk of whether this could potentially result in the chemical erosion of some seal lithologies leading to leakage needs to be addressed. In most instances, because of their low [[permeability]] and [[Capillary pressure|capillary properties]], CO₂ is unlikely to enter seals. Therefore, any potential reactions are likely to be limited to the base of the seal. In addition, because the [http://chemistry.about.com/od/chemistryglossary/a/phdef.htm pH] buffering capabilities of the seal lithology are generally greater than the dissolution capabilities of carbonic acid, reactions are likely to be mineral precipitation instead of dissolution, thus leading to seal capacity enhancement instead of degradation.<ref name=Watsonetal_2005>Watson, M. N., R. F. Daniel, P. R. Tingate, and C. M. Gibson-Poole, 2005, CO₂-related seal capacity enhancement in mudstones: Evidence from the pine lodge natural CO₂ accumulation, Otway Basin, Australia, in M. Wilson, T. Morris, J. Gale, and K. Thambimuthu, eds., Greenhouse gas control technologies: Proceedings of the 7th International Conference on Greenhouse Gas Control Technologies: Oxford, Elsevier, v. 2, part 2, p. 2313–2316.</ref>