A few subgroups identified crosscutting technical issues that were not carbon management ideas per se but rather engineering and analytical issues associated with long-term carbon storage. Three such issues are described below.
Once CO2 is sequestered in the subsurface by some means, it will be necessary to monitor the sequestered CO2 to determine whether leakage is occurring. By necessity, detection technologies must be low in both capital and operating costs, highly sensitive, and capable of monitoring large areas of Earth’s surface. The latter capability is essential, because the sequestered CO2 may be spread out over large areas of the subsurface.
Equally vital are technologies that will be able to heal leaks in the subsurface. Sequestration of CO2 may take different forms, ranging from storage in saline aquifers and deep subsurface coal beds to deep-ocean disposal methodologies; therefore, technologies to seal leaks must be diverse and effective in a range of subsurface environments.
CO2 is likely to be stored in a variety of forms, ranging from pressurized CO2 in subsurface environments to immobile mineralized forms. In some storage scenarios, the liquefied CO2 will seek cracks and fractures in the geologic formation, abandoned wells in depleted oil fields, wormholes in the deep-ocean sediment storage areas, or tears in such proposed storage methods as deep-sea bladders filled with CO2. Although catastrophic CO2 release is unlikely in most storage schemes, slow leakage is likely. These slow leaks not only must be identified but also must be effectively repaired to ensure secure storage of the carbon for long periods of time.
Monitoring technology must be capable of detecting CO2 leaks through the existing atmosphere, on the terrestrial surface, on the ocean surface, and in the deep ocean. Technology concepts for monitoring could include such things as “tagging” the stored CO2 with an odorant such as hydrogen sulfide (H2S) or a mercaptan that could be detected by gas analyzers, radioactive isotopes that could be traced, or spectrally detected compounds such as sulfur hexafluoride (SF6). Hyperspectral satellite imagery or change-conditions technology in a global monitoring context may offer technical opportunities for monitoring. For deep-ocean disposal, such as in a pressurized bladder that resides on the deep-ocean floor, an array of pH meters to monitor changes in ocean water pH may be sufficient.
Highly effective sealing technologies that can be employed remotely in the deep subsurface environment or the deep ocean must be identified and engineered. Opportunities may exist in technological extensions to conventional grouting methods, new polymer sealants may be developed, or biofilms and other biological methods may be developed for selectively sealing leaks. Promising technological developments need to be tested for effectiveness as engineered barriers to CO2 mobilization.