U42A-01 INVITED
Geological Storage as a Carbon Mitigation Option
One of the most promising approaches for carbon mitigation involves essentially-zero-emission power plants based on carbon capture and storage (CCS) technology. The key to any CCS strategy is a suitable choice for large-scale storage of the captured CO2. While a variety of storage options are being studied, geological storage appears to be most viable. Injection of captured CO2 into deep geological formations leads to a fairly complex flow system involving multiple fluid phases, a range of potential geochemical reactions, and mass transfer across phase interfaces. General models of this system are computationally demanding, with the problem made more difficult by the large range of spatial scales involved as well as the importance of local features for both fluid flow and geochemical reactions. An especially important local feature involves leakage pathways, with one example being abandoned wells associated with the century-long legacy of oil and gas exploration and production. Such pathways also have large uncertainties associated with their properties. Therefore, inclusion of leakage in the storage analysis requires resolution of multiple scales and incorporation of large uncertainties. Furthermore, when implemented at full scale, geological storage will induce subsurface perturbations that extend across entire basins. Taken together, these requirements render standard numerical simulators ineffective due to their excessive computational demands. A series of physically-motivated simplifications to the governing equations can ultimately render the system solvable by analytical or semi-analytical methods. These solutions, while restrictive in their assumptions, allow for large-scale analysis of leakage in a probabilistic framework and can provide a basis for regulatory policies.
U42A-02 INVITED
A Controlled Field Pilot for Testing Near Surface CO2 Detection Techniques and Transport Models
A field facility has been developed to allow controlled studies of near surface CO2transport and detection technologies. The key component of the facility is a shallow horizontal, well slotted over 70m of its length and divided into seven zones via packers with mass flow control in each individual zone. The scale and fluxes were designed to address large scale CO2 storage projects and desired retention rates for those projects and those design parameters will be discussed. A wide variety of detection techniques were deployed by collaborators from Los Alamos National Lab, Lawrence Berkeley National Lab, the National Energy Technology Lab, Pacific Northwest National Lab, Lawrence Livermore National Lab and West Virginia University. Techniques included eddy covariance, soil gas measurements, hyperspectral imaging for plant stress detection, differential absorption LIDAR (both free space atmospheric and below surface soil gas), tracer studies, water sampling, stable isotope studies, and soil flux chambers. An overview of these results will be presented.
U42A-03 INVITED
Carbon Storage in Biologic and Oceanic Reservoirs: Issues and Opportunities
Most discussion of carbon capture and storage have focused on geologic reservoirs because these are the reservoirs most likely to provide for long-term storage with a minimum of adverse environmental consequences. Nevertheless, there is interest in storage in other reservoirs such as the biosphere or the oceans. Storage in biological reservoirs such as forests or agricultural soils may in many cases be relatively inexpensive. Because this biological storage involves carbon dioxide removal from the atmosphere, it can potentially offset emissions from the transportation sector. Biological storage can be politically popular because it can be deployed with simple technologies, can be deployed in developing countries, and in many cases involves other environmental co-benefits. However, total capacity is limited. Furthermore, biological storage is temporary unless the store is actively maintained forever. Such temporary storage can be valuable, although it is clearly not as valuable as the quasi-permanent storage offered by good geologic storage reservoirs Ocean storage options fall into two main classes. The first involves conventional separation and compression of carbon dioxide from large point sources which would then be piped into the deep ocean and released either into the water or as a lake on the sea floor. In either case, the carbon dioxide would eventually interact with the atmosphere and contribute to ocean acidification. However, there is potential for the development of long-term engineered containment of carbon dioxide on or in the sea floor. The second main ocean storage option involves increasing ocean alkalinity, probably by dissolving carbonate minerals. This approach may offer safe, quasi- permanent, and cost-effective storage in settings where coastal carbon dioxide point sources are co-located with carbonate mineral deposits. Not every location or carbon dioxide source is suitable for geologic storage of carbon dioxide. At this early stage, it is important not to foreclose options that may, with further development, provide for long-term, safe, and cost- effective storage of carbon dioxide.
U42A-04
Viability of Carbon Dioxide Storage in Deep Sea Sediment
Despite the public's general aversion to using the ocean to dispose of captured carbon dioxide (CO2), recent revisions of the London Protocol have removed a hurdle to subsea injection of CO2. This paper constructs a map of the worldwide "prospectivity" of CO2 storage in deep sea sediment, i.e. amenable locations are determined and storage capacities estimated. CO2 injected into deep sea sediment is expected to be gravitationally trapped and secondarily capped by CO2 hydrate formation. Capture, transport, and storage costs are estimated and a mixed-integer linear programming model that generates spatially optimized infrastructure networks is applied. The model captures CO2 from fixed point sources, uses minimum cost routing paths, aggregates CO2 flow into trunk distribution pipelines where appropriate, and injects the CO2 in potential deep sea injection sites. Economies of scale for this climate change mitigation intervention in the United States Exclusive Economic Zone are discussed, including provisions for destabilizing and/or harvesting methane from in situ gas hydrates.
U42A-05
The role of carbon dioxide capture from ambient air in the portfolio of mitigation options
CO2 capture from ambient air acts directly on the atmospheric CO2 concentration, and thus provides increased leverage to control the carbon cycle. We ask the question how the increased leverage will be utilized when CO2 air capture is added to a portfolio of classic mitigation options: increasing energy efficiency, substitution of fossil fuels, and carbon capturing and storage at point sources. It can be expected that the value of CO2 air capture will strongly depend on its costs, the long-term climate policy target, and climate sensitivity. The coupled economy-climate model MIND1.2 allows the investigation of cost-effective mitigation policies for achieving ambitious temperature and concentration targets. We have upgraded the model with a stylized CO2 air capture module based on the work of Stolaroff and Keith (J. K. Stolaroff, Capturing CO2 from ambient air: A feasibility assessment, PhD thesis, Carnegie Mellon University). We use the upgraded model to explore the cost-effective use of CO2 air capture vs. classic mitigation options for various targets and climate sensitivities.
U42A-06
Terrestrial Carbon Sequestration with Biochar: A Preliminary Assessment of its Global Potential
Biochar technology involves the capture of CO2 from the atmosphere by photosynthesis and its ultimate conversion to biochar by pyrolysis. Energy is obtained during the pyrolysis process and the charcoal, or biochar, which is considerably more stable than biomass, may then be incorporated into agricultural lands where it serves to increase the nutrient- and water-holding capacity of soil. With an estimated half-life in soil on the order of centuries to millenia, biochar offers a way of safely storing C for long periods of time while enhancing the productivity of terrestrial ecosystems. Moreover, biochar technology, like other biomass conversion approaches that include C sequestration options, offers a way to decrease the levels of CO2 in the atmosphere. That is, biochar technology is one of the few inherently "carbon-negative" sources of energy. These positive attributes are of little consequence, however, if the total contribution to sequestration is small compared to the need. In this paper, we provide a preliminary assessment of the potential contribution of biochar technology to the mitigation of climate change, and identify some research needs. Currently, the atmospheric C levels are increasing by about 4.1 Gt/yr, with 7.2 Gt/yr being put into the atmosphere by fossil fuel combustion and cement production, and 3.1 Gt/yr being removed from the atmosphere by the ocean (2.2 Gt/yr) and terrestrial processes (0.9 Gt/yr). The uptake by terrestrial processes can be increased significantly by management of the 60.6 Gt/yr of biomass C that is fixed by photosynthesis (i.e., net primary productivity), of which 59 Gt/yr is decomposed and 1.6 Gt/yr combusted. Biomass pyrolysis converts about 50% of the biomass C to char. Of the other 50% that is converted to bio-oil and bio-gas, the net energy production is about 62% efficient. Thus, pyrolysis of 1 Gt of biomass C would provide energy equivalent to about 0.3 Gt of fossil C and could be used to offset that amount of fossil C, while sequestering 0.5 Gt as biochar. Of the 60.6 Gt/yr of biomass that is fixed in usable form, we estimate that perhaps 10% of it (6.1 Gt/yr) could become available in one form or another (crop and forestry residues, and animal waste) for pyrolysis. This level of pyrolysis would offset 1.8 Gt/yr of fossil C, and sequester 3.0 Gt/yr as biochar, enough to halt the increase and actually decrease the level of atmospheric C by 0.7 Gt/yr. Even at half this level (i.e., 5% of annually fixed biomass), pyrolysis would be sufficient to decrease the global C cycle imbalance by 2.4 Gt/yr and in combination with other sequestration options help to achieve the minimum goal of C neutrality. Clearly, the potential contribution of biochar technology is large, perhaps large enough to mitigate climate change alone. However, this preliminary assessment is tempered by several unknowns. Research is needed to further define the impacts of biochar amendments on soil biota, productivity, and greenhouse gas production. For example, there is some evidence that N2O and CH4 production is decreased by biochar amendments, but the mechanisms responsible are unknown. The impact of different types of biochar and pyrolysis conditions also needs to be determined. Lastly, total accounting for greenhouse gas emissions coupled with economic analyses to determine the economic potential of the technology under various scenarios is essential.
U42A-07
Carbon Sequestration via Wood Burial
To mitigate global climate change, a portfolio of strategies will be needed to keep the atmospheric CO2 concentration below a dangerous level. Here a carbon sequestration strategy is proposed in which forest dead wood or old trees are harvested via collection or selective cutting, then buried in trenches or stowed away in above-ground shelters. The largely anaerobic condition under a sufficiently thick layer of soil will prevent the decomposition of the buried wood. Because a large flux of CO2 is constantly being assimilated into the world's forests via photosynthesis, cutting off its return pathway to the atmosphere forms an effective carbon sink. It was estimated that the carbon sequestration potential of forest wood harvest and burial is 10GtC y-1 with an uncertainty range of 5-15 GtC y-1. Based on data from North American logging industry, the cost was crudely estimated at $50/tC, significantly lower than the cost for power plant CO2 capture with geological storage, a carbon sequestration technique currently under most serious consideration. The low cost is largely because the CO2 capture is achieved at little cost by the natural process of photosynthesis. The technique is low tech, distributed, safe and can be stopped or reversed at any time. The relatively low cost may soon be competitive enough for large-scale implementation in a world-wide carbon trading market. In tropical regions with ongoing deforestation, wood burial instead of burning will immediately reduce that portion of the anthropogenic CO2 emission.