Changes

==Monitoring==

==Monitoring==

In addition to the careful selection of the subsurface formation, a comprehensive monitoring system needs to be put in place to verify that the CO₂ remains in the subsurface. Monitoring of the activities of stored CO₂ includes an extensive range of established direct and remote sensing technologies, including petrophysical, geophysical, and geochemical methodologies deployed on the surface and in the borehole. These are used for repeated assessments from a reservoir, containment, wellbore integrity, near-surface, and atmospheric perspective.<ref name=Doddsetal_2006>Dodds, K., D. Sherlock, M. Urosevic, D. Etheridge, D. de Vries, and S. Sharma, 2006, Developing a monitoring and verification scheme for a pilot project, Otway Basin, Australia, in N. A. Rokke, O. Bolland, and J. Gale, eds., Greenhouse gas control technologies: Proceedings of the 8th International Conference on Greenhouse Gas Control Technologies: Trondheim, Norwegian University of Science and Technology (NTNU), SINTEF Technology (SINTEF), and International Energy Agency (IEA) Greenhouse Gas RampD Program, 6 p.</ref> Wellbore properties such as pressure, temperature, resistivity, and sonic responses can be recorded in injection and observation wells. Geophysical monitoring involves quantification of 3-D and seismic time-lapse imaging of the plume and its migration. This is done using an array of methodologies, including vertical seismic profile (VSP), microseismic data, electromagnetic imaging (EM), and gravity to track the movement of CO₂ in the subsurface.<ref name=Doddsetal_2006 /> This process involves calibration with laboratory determination of in-situ geophysical properties associated with CO₂ and developing predictive forward modeling of the behavior of CO₂. Detailing results of such modeling and possible acquisition effects on seismic imaging are provided by Arts<ref name=Artsetal_2009>Arts, R. J., R. A. Chadwick, O. Eiken, S. Dortland, M. Trani, and L. G. H. van der Meer, 2009, [http://archives.datapages.com/data/specpubs/study59/CHAPTER22/CHAPTER22.HTM Acoustic and elastic modeling of seismic time-lapse data from the Sleipner CO₂ storage operation], in M. Grobe, J. C. Pashin, and R. L. Dodge, eds., Carbon dioxide sequestration in geological media—State of the science: AAPG Studies in Geology 59, p. 391–403.</ref> who describe the injection of CO₂ in the Utsira Sand at Sleipner (ongoing since 1996 with almost 10 million tonnes of CO₂ injected to date).

In addition to the careful selection of the subsurface formation, a comprehensive monitoring system needs to be put in place to verify that the CO₂ remains in the subsurface. Monitoring of the activities of stored CO₂ includes an extensive range of established direct and remote sensing technologies, including petrophysical, geophysical, and geochemical methodologies deployed on the surface and in the borehole. These are used for repeated assessments from a reservoir, containment, wellbore integrity, near-surface, and atmospheric perspective.<ref name=Doddsetal_2006>Dodds, K., D. Sherlock, M. Urosevic, D. Etheridge, D. de Vries, and S. Sharma, 2006, Developing a monitoring and verification scheme for a pilot project, Otway Basin, Australia, in N. A. Rokke, O. Bolland, and J. Gale, eds., Greenhouse gas control technologies: Proceedings of the 8th International Conference on Greenhouse Gas Control Technologies: Trondheim, Norwegian University of Science and Technology (NTNU), SINTEF Technology (SINTEF), and International Energy Agency (IEA) Greenhouse Gas RampD Program, 6 p.</ref> Wellbore properties such as pressure, temperature, resistivity, and sonic responses can be recorded in injection and observation wells. Geophysical monitoring involves quantification of 3-D and seismic time-lapse imaging of the plume and its migration. This is done using an array of methodologies, including vertical seismic profile (VSP), microseismic data, electromagnetic imaging (EM), and gravity to track the movement of CO₂ in the subsurface.<ref name=Doddsetal_2006 /> This process involves calibration with laboratory determination of in-situ geophysical properties associated with CO₂ and developing predictive forward modeling of the behavior of CO₂. Detailing results of such modeling and possible acquisition effects on seismic imaging are provided by Arts<ref name=Artsetal_2009>Arts, R. J., R. A. Chadwick, O. Eiken, S. Dortland, M. Trani, and L. G. H. van der Meer, 2009, [http://archives.datapages.com/data/specpubs/study59/CHAPTER22/CHAPTER22.HTM Acoustic and elastic modeling of seismic time-lapse data from the Sleipner CO₂ storage operation], 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. 391–403.</ref> who describe the injection of CO₂ in the Utsira Sand at Sleipner (ongoing since 1996 with almost 10 million tonnes of CO₂ injected to date).

Nonseismic techniques, such as electrical properties, the monitoring of injection processes with changes in stress state, and detecting potential fracture processes through passive seismic measurements, may also be added to the monitoring array. Including geochemical and hydrodynamic sampling to ensure that the injected CO₂ has not leaked from its container and hence verify the integrity of seals is also important. Adding tracers to the injected CO₂, combined with sampling at surface localities, allows rapid detection of any seepage or leakage in the unlikely circumstance that this should occur. Near-surface and surface (soil, water well, and atmospheric) monitoring devices, including tracer and isotope analysis, can be deployed to determine the flux and composition of CO₂ and to distinguish anthropogenic and natural sources of CO₂ from injected CO₂.

Nonseismic techniques, such as electrical properties, the monitoring of injection processes with changes in stress state, and detecting potential fracture processes through passive seismic measurements, may also be added to the monitoring array. Including geochemical and hydrodynamic sampling to ensure that the injected CO₂ has not leaked from its container and hence verify the integrity of seals is also important. Adding tracers to the injected CO₂, combined with sampling at surface localities, allows rapid detection of any seepage or leakage in the unlikely circumstance that this should occur. Near-surface and surface (soil, water well, and atmospheric) monitoring devices, including tracer and isotope analysis, can be deployed to determine the flux and composition of CO₂ and to distinguish anthropogenic and natural sources of CO₂ from injected CO₂.