8.8 Recommendations
Several CO2 storage projects are now in operation and being carefully monitored. No leakage of stored CO2 out of the storage formations has been observed in any of the current projects. Although time is too short to enable direct empirical conclusions about the long-term performance of geological storage, it is an indication that CO2 can be safely injected and stored at well characterized and properly managed sites. Monitoring of existing projects in the coming 10-20 years is crucial to the broader understanding of CO2 transport, trapping mechanisms and storage security and to predict long-duration performance. However, if leaks occur, tools for monitoring possible local and regional environmental hazards should be in place together with remediation measures. In this section general recommendations which are thought to contribute to better understanding of geological storage of CO2 with regard to security and environmental safety. Also the measures needed to be taken in future are listed below.
1) Storage capacity determination for large scale carbon dioxide storage should be determined as accurately as possible. The problem of heterogeneity and porosity should be assessed carefully. Reaction of the CO2 with formation water and rocks may result in reaction products that affect the porosity of the rock and the flow of solution through the pores. This possibility has not been observed experimentally and its possible effects are not quantified. It is important to assess these effects to get better knowledge about the reservoir and migration patterns of the injected CO2.
2) During site characterization greatest emphasis are placed on the reservoir and its
sealing horizons. However, the strata above the storage formation and caprock also need to be assessed because if CO2 leaked it would migrate through them.
3) Geological storage projects will be selected and operated to avoid leakage. However,
in rare cases, leakage may occur and remediation measures will be needed, either to stop the leak or to prevent human or ecosystem impact. Moreover, the availability of remediation options may provide an additional level of assurance to the public that geological storage can be safe and effective. Therefore appropriate remediation options must be identified in an event of a leakage scenario.
4) The Utsira Formation is a very large aquifer with a thick and extensive claystone top seal. The aquifer is, however, unconfined along its margins. It is important to assess the time required for the migrating CO2 to reach at the margins of the aquifer.
5) To predict the migration of CO2 over a period of several thousand years a coarse grid
model was used due to computational constraints. However, grid patterns may miss
narrow linear anomalies or patterns of linear features on the surface that may reflect deeper fault and fracture systems, which could become natural migration pathways. Future modelling should account such uncertainties.
6) During the SACS project (Best Practice Manual, 2004), the lack of observation boreholes and related samples made it impossible to monitor directly the geochemical processes occurring within the Utsira at Sleipner. Also the interactions of CO2 with
borehole cement were not addressed in the study. Assessment of both issues should be a priority in future monitoring activities.
7) Evaluations on the risk of leakage through injection well, seal, and stress release events due to injection of CO2 and their probabilities on the release of CO2 should be a priority. Moreover, quantification of the short-term and long-term Health-Safety- Environmental (HSE) risks, in this case the likelihood of impacts on human and marine life should be assessed.
8) Finally further research on the processes involved in both sealing and in migration of CO2 in the underground and improved modelling tools is needed to predict future behaviour of a storage location. Modelling tools need to be improved through calibration on real life experiments. Demonstration under different geological conditions is also pointed as important both for improving the understanding but also to prove to the public that storage are safe.
8.8 Recommendations
Several CO2 storage projects are now in operation and being carefully monitored. No leakage of stored CO2 out of the storage formations has been observed in any of the current projects. Although time is too short to enable direct empirical conclusions about the long-term performance of geological storage, it is an indication that CO2 can be safely injected and stored at well characterized and properly managed sites. Monitoring of existing projects in the coming 10-20 years is crucial to the broader understanding of CO2 transport, trapping mechanisms and storage security and to predict long-duration performance. However, if leaks occur, tools for monitoring possible local and regional environmental hazards should be in place together with remediation measures. In this section general recommendations which are thought to contribute to better understanding of geological storage of CO2 with regard to security and environmental safety. Also the measures needed to be taken in future are listed below.
1) Storage capacity determination for large scale carbon dioxide storage should be determined as accurately as possible. The problem of heterogeneity and porosity should be assessed carefully. Reaction of the CO2 with formation water and rocks may result in reaction products that affect the porosity of the rock and the flow of solution through the pores. This possibility has not been observed experimentally and its possible effects are not quantified. It is important to assess these effects to get better knowledge about the reservoir and migration patterns of the injected CO2.
2) During site characterization greatest emphasis are placed on the reservoir and its
sealing horizons. However, the strata above the storage formation and caprock also need to be assessed because if CO2 leaked it would migrate through them.
3) Geological storage projects will be selected and operated to avoid leakage. However,
in rare cases, leakage may occur and remediation measures will be needed, either to stop the leak or to prevent human or ecosystem impact. Moreover, the availability of remediation options may provide an additional level of assurance to the public that geological storage can be safe and effective. Therefore appropriate remediation options must be identified in an event of a leakage scenario.
4) The Utsira Formation is a very large aquifer with a thick and extensive claystone top seal. The aquifer is, however, unconfined along its margins. It is important to assess the time required for the migrating CO2 to reach at the margins of the aquifer.
5) To predict the migration of CO2 over a period of several thousand years a coarse grid
model was used due to computational constraints. However, grid patterns may miss
narrow linear anomalies or patterns of linear features on the surface that may reflect deeper fault and fracture systems, which could become natural migration pathways. Future modelling should account such uncertainties.
6) During the SACS project (Best Practice Manual, 2004), the lack of observation boreholes and related samples made it impossible to monitor directly the geochemical processes occurring within the Utsira at Sleipner. Also the interactions of CO2 with
borehole cement were not addressed in the study. Assessment of both issues should be a priority in future monitoring activities.
7) Evaluations on the risk of leakage through injection well, seal, and stress release events due to injection of CO2 and their probabilities on the release of CO2 should be a priority. Moreover, quantification of the short-term and long-term Health-Safety- Environmental (HSE) risks, in this case the likelihood of impacts on human and marine life should be assessed.
8) Finally further research on the processes involved in both sealing and in migration of CO2 in the underground and improved modelling tools is needed to predict future behaviour of a storage location. Modelling tools need to be improved through calibration on real life experiments. Demonstration under different geological conditions is also pointed as important both for improving the understanding but also to prove to the public that storage are safe.
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