CO2 Environmental issues

Environmental issues

Accidental release of hazardous substances from the power plant will have to be detected and mitigation plans will have to be established. In addition to instrumentation, monitoring the local biota can give indications of unwanted releases. Scenarios for releases to the atmosphere may be analyzed using the same type of CFD tools as used for analyzing the development of clouds of combustible gases.

Each CO2 storage project will have to develop an adequate and unique monitoring program that will have to fulfill two main criteria; demonstrate that the reservoir performance meets the defined standards, yet to be established, and assure that migration or leakage does not occur.

Mitigation plans should be available if a migration is detected, and the monitoring program changed accordingly. Hence, the monitoring program should be flexible and be subject to changes both during and after the injection. In order to be able to have adequate mitigation options a migration out of the reservoir should be detected as early as possible. However, the resolution of the monitoring tools makes accurate measurements of volume of CO2   inside the reservoir uncertain, and detection of small migrations and seeps difficult. A leakage to the atmosphere or ocean may occur over a large area, and dispersed small leakages may occur which will be difficult to detect. In order to detect a leak to ocean, it will be important to monitor changes in benthic and aquatic chemistry.

The monitoring might be expected to last for several years into the post injection period and cover an area of up to 100 km². Hence reliable and durable instrumentation will have to be developed. A gradual downscaling of the program could be initiated once specific events have occurred. For instance a specific fault has been reached without detection of a leakage, a large fraction of the CO2 has been dissolved into reservoir fluid (becoming negative buoyant), or mineral trapping can be assured.

Leakage or migration of other substances mobilized by CO2 reactions is another issue. Examples are the possibility of increased levels of heavy metals in potable groundwater, and release of methane. The behavior of this aggressive greenhouse gas is different from CO2, e.g. it is much less solvable in water. Through reactions or new migration pathways there is a possibility that CO2 injection may trigger a CH4 leakage.

How microbial dynamics responds to the presence of either supercritical CO₂ in deep formations is not only an important scientific question, but is also of key relevance in the design and management of geological CO₂ storage schemes.  For example, the formation of biofilms in the vicinity of injection wells might affect flow distributions and overall injection pressure required to maintain a suitable injection rate.  There is little if any information on how bacterial and biofilm dynamics are affected once they are in direct contact with supercritical CO₂. Concerns have also been raised about the possibility that geological storage of CO₂ may change the native microbial populations and result in the loss of biodiversity.  The extent of these biogeochemical changes will be important not only for an overall risk assessment of the CO₂ injection option, but they may also be used to indicate elevated CO₂ levels and therefore serve as indicators for CO₂ leakage.

It will be important to detect leaks of CO2   to the atmosphere, lakes or the ocean. The most dramatic, but also easiest to detect, will be a pipeline failure or major blowout from injection or monitoring wells. But also dispersed leaks will be important to detect. CO2  is nontoxic in low concentrations, but may have environmental impact and a leakage will reduce the benefit of storing CO2. High concentrations of CO2 may cause asphyxiation, primarily by replacing oxygen, and hence is potentially lethal. Hence, a program for monitoring areas prone for CO₂ accumulation might have to be established. 

Related to Mongstad and Norwegian storage scenarios a leakage to oceanic waters is most likely. It will be important to detect such a leakage, which may occur over a large area, as early as possible. Hence large areas will have to be monitored for elevated levels of CO₂, both within the benthic layer and in the water column. The benthic biota can give an early indication of a dispersed leak. How effective the ocean might serve as a buffer, preventing further release to the atmosphere, needs to be clarified.

Chronic or acute influences on the marine biota from elevated CO₂ concentrations are still not yet fully understood. Especially cold-water calcifying organisms, which build their external skeletal material out of calcium carbonate, is expected to be highly sensitive to elevated CO₂ content in the sea water. Since these organisms provide food and habitat to others, it might have strong influence on the entire ocean ecosystem.

Reduced Ca may result in dissociation of the respiratory pigments (haemocyanins) of marine gastropods and crustaceans that will cause osmotic stress and death. It is general believed that fish do not have CO₂ sensors, and will therefore encounter hypercapnia (high blood CO₂ levels) very easily. This is a particular problem for fish in dense populations such as fish farms, where high CO₂ output is a major problem.  

Since Mongstad is supposed to be a pilot project for development of CO₂ handling technology, studies on environmental impact from an atmospheric leak should not be excluded.

Even though we must assume that the site selection process will lead to exclusion of storage sites which are not suitable in the long term, the risk of leakage cannot be ruled out completely. Viewed in this light, acceptable potential leakage rates to the atmosphere over time as compared to doing nothing is part of the ongoing debate.

This issue is complex and will be highly cross-disciplinary, each of the partners has significant competence that combined will make them suitable for pursuing all aspects