U43C-1377
Experimental and Numerical Study of CO2 Sequestration in Geologic Formations.
Sequestration of carbon dioxide in geologic formations is the most effective method of reducing the impact of global warming. Experiments at the laboratory scale are presented to investigate the influence of gravitational, viscous and capillary effects on the sequestration process. Experiments are performed in the parameter range of practical flows associated with CO2 sequestration and are carried out primarily to investigate the type of flow regimes expected. We demonstrate the existence of pore scale instability in the presence of unfavorable gradients of viscosity and density, which cannot be modeled by conventional means such as continuum Darcy equations. A comparison with theoretical estimates from gradient percolation theory shows good agreement with experimental observations. Numerical simulations based on pore network models are carried out to determine the correct conductivity relation as a function of various parameters.
U43C-1378
Formation Buffering Potential Pertaining to Geological Storage of Carbon Dioxide
One promising strategy for decreasing CO2 emissions to the atmosphere is carbon capture and storage in deep saline formations. Modeling efforts and the experimental measurements that support these efforts are critical to determining the fate of injected CO2. The focus of this work is CO2-water-rock interactions as they pertain to formation buffering potential. PHREEQC was used to model pH evolution in siliciclastic and carbonate rocks after simulated injection of CO2. The initial mineral and formation water compositions were determined from analysis of core samples and brines from several formations in the Alberta sedimentary basin in western Canada. Simulation parameters correspond to injection conditions of 50°C, CO2 pressure of 100 bar and high ionic strength. Results indicate that the carbonate formations have a higher buffering potential relative to siliciclastic formations. Considerable variability of acid-catalyzed reactions among formations with similar mineralogical compositions was also observed. To assess the effect of grain coating by clay minerals, a comparative simulation was performed with kaolinite as the dominant mineral in contact with the pore fluids. Results from this simulation showed a pronounced retardation in pH buffering reaction kinetics. This emphasizes the importance for differentiating between mineral abundance and accessibility in model calculations when clay coatings may obscure contact between pore fluids and potentially reactive minerals.
U43C-1379
Experimental alteration of peridotite during injection of CO2-rich fluids
CO2 sequestration by direct injection into geological formation is a highly regarded option for reducing greenhouse gas emissions. Carbonation of ultramafic rocks is the most efficient reaction to trap CO2 into stable carbonate phases. Thus, widespread ultramafic bodies represent an immense storage capacity by long-term hydrothermal processes (slow-spreading ridges) and by industrial injection of CO2-enriched fluids. A critical issue for durability of both processes is the prediction of consequences of fluid circulation/injection on rock properties. Yet, fundamental parameters characterizing in situ reactions of CO2-enriched fluids in ultramafic rocks and their consequences on hydrodynamic properties are lacking. We investigate these processes by scaled rock sample percolation experiments. We present results of experiments performed using sintered grounded dunite (96.5% olivine, 2% diopside, 1.5% spinel) flooded at constant specific discharge (0.6 ml/min) with CO2-enriched fluid up to PCO2 = 95 bars, under a confined pressure of 120 bars and a temperature of 160C. Permeability stabilizes after an increase period of 1h. The chemical composition of the outlet fluid is dominated by Si and is depleted in Mg relative to stoechiometric dissolution of olivine during the whole experiment. SEM imaging of the central part of the core sample reveals an increase in porosity starting in the vicinity of the fluid inlet and propagating toward the core outlet. Behind this reaction front, diopside grains are preferentially altered. A porous and poorly crystallized material is observed around diopside and olivine grains. EDS-TEM is required to characterize the neoformed material. Mg-enriched carbonates develop locally on olivine grains, preferentially in the vicinity of diopside. Olivine and carbonate are separated by a porous interface made of a poorly crystallized Si- rich gel and nanograins of magnetite. Gel composition varies between talc and serpentine stoechiometry. These results show that carbonation is rapid and overcome serpentinization under those conditions (xCO2 = 0.8). The existence of the porous reactive interface promotes fluid renewal at the olivine surface, and allows reaction to persist despite the carbonate formation. Pressure loss (permeability), measured across the sample, is constant during the experiment independently on the fluid-rock mass transfers. Probably the permeability increase due to the increase of the nanoporosity by dissolution is balanced by the increasing pressure loss induced by the gel formation. Long-lasting experiments are presently run to test the limit of this process.
U43C-1380
Enhanced Natural Carbon Sequestration in Tectonically Exposed Mantle Peridotites
Carbon sequestration via mineral carbonation of calcium and magnesium silicates has been proposed but efficient carbonation is limited by the cost and energy requirement associated with mineral pretreatment (grinding, heating). Weathering of tectonically exposed mantle peridotite (rich in olivine and minor pyroxene) forms solid carbonate minerals (magnesite, hydrated magnesite, and calcite) during interaction between ground water and either olivine and pyroxene, or their main hydration product, serpentine. Carbonates are deposited in veins and as interstitial minerals within weathered peridotites, and at the surface where alkaline, Ca-rich, CO2-poor spring waters formed during serpentinization combine with atmospheric CO2 to form large travertine deposits. Literature data and our new analyses of alkaline spring waters emerging from peridotite section of the Samail Ophiolite in the Sultanate of Oman, suggest that 10 to 100 times more CO2 is deposited in subsurface carbonate veins, compared to the volume of travertine formed on the surface. New radiocarbon ages show that both carbonate veins and travertine deposits in the large, tectonically exposed peridotite section of the Samail Ophiolite, formed on average in the past ~20,000 years. Using these data, we estimate that the approximate present day natural carbon sequestration rate is ~1E9 kg of CO2 per year. This process is not particularly efficient, but the available mass of olivine, pyroxene and serpentine is large. Present day carbonation in Oman is restricted to the upper few 10's of meters, whereas the peridotite massif is several km thick in places. Thus, drilling and hydrofracturing, followed by forced circulation of meteoric or seawater, would likely enhance carbonation rates significantly. Carbonation rates may also be enhanced by exploiting the chemical potential energy inherent in exposing CO2- and H2O-poor mantle peridotite to the ocean and atmosphere. We present a simple 1D model that quantifies past suggestions that exothermic hydration of olivine and pyroxene to form serpentine can heat surrounding rocks. Heating, in turn, enhances hydration rates until temperature approaches the thermal stability limit of serpentine. Heating can be tuned to maintain near-constant temperature close to the optimal olivine carbonation rate, so that carbonation rates potentially increase 100 or 1000-fold compared to present day
U43C-1381
In-situ Carbonation of Magnesium Silicates: an Experimental Investigation of the Sequestration Potential of Oceanic Crust
A promising solution to the problem of anthropogenic greenhouse carbon is through carbonation of ultramafic minerals. Investigations of the carbonation potential of magnesium silicate minerals in industrial settings have been conducted, but the process is energy intensive and expensive. Direct injection of carbon dioxide into seafloor hydrothermal systems that are rich in magnesium silicate minerals may provide an alternate, viable pathway for sequestering carbon dioxide. Experiments were conducted on seawater-oceanic crust-carbon dioxide systems to simulate injection of carbon dioxide into a seafloor hydrothermal system and determine the extent of fluid-rock reaction. The solid reactant was comprised of 71.4% olivine, 18.4% diopside, and 10.2% enstatite. This proxy for oceanic crust was reacted at 300 C and 500 bar in a synthetic seawater solution to approach steady state, then injected with supercritical carbon dioxide and reacted for 550 hours. Three mole percent of carbon dioxide relative to water was injected into the experimental system. The experimental pressure decreased 17 bars in three hours following carbon dioxide injection due to initial dissolution and mineralization of carbon dioxide. The pressure decreased an additional 20 bars due to mineralization during the remainder of the experiment. Approximately 20% of injected carbon dioxide was mineralized, and the remainder was dissolved into the aqueous fluid. Brine-rock reaction decreased pH from 7.4 to 5. Aqueous calcium was consumed following carbon dioxide injection, whereas magnesium and silica concentrations increased due to increased brine acidity. Mineral reactants dissolved, as indicated by surface pits and etching on mineral fragments and the increase of aqueous magnesium and silica concentration. Mineral reactants were serpentinized, and then reacted to talc and magnesite following carbon dioxide injection. Magnesite comprised approximately 30 weight % of the reaction products. Carbon dioxide dissolution and attendant magnesite precipitation indicates that direct injection of carbon dioxide into oceanic crust may be a viable means of sequestering anthropogenic carbon.
U43C-1382
A global assessment of deep-sea basalt sites for carbon sequestration
Assuring secure sequestration of anthropogenic carbon dioxide is one of our most pressing global scientific problems. Geological sequestration by injection of carbon dioxide into deep-sea basalt formations offers unique and significant advantages, such as: high porosity and permeability to accommodate large injected volumes, chemical reactivity of these formations with in situ fluids to produce stable and non-toxic carbonates, and reduced risk of post-injection leakage through geological, gravitational, and hydrate trapping mechanisms. We explore the scientific potential of deep-sea basalt locations among various oceans for long-term carbon sequestration. Using site-specific criteria to highlight the most secure sites, we identify potential target regions that occur along the flanks of oceanic ridges and compute the potential injection volume for each. The largest volume and most secure basalt sites occur in regions adjacent to intermediate-to-fast spreading mid-ocean ridges as well as deep aseismic ridges. We suggest that basalt crust along the flanks of such ridges offers vast capacity and potential for permanent sequestration of carbon dioxide to mitigate atmospheric buildup of this greenhouse gas.
U43C-1383
A KEY FOR ‘STABLE' SEQUESTRATION OF CO2 IN GEOLOGICAL RESERVOIRS: THE FORMATION OF CARBONATE MINERALS
CO2 injections in brine aquifers strongly modify the physic and the chemistry of the host aquifer affecting mainly the calcite precipitation kinetics. Classically precipitation laboratory experiments link the precipitation rate (the dependent variable) to one or more independent variables. In this work we evaluated the mutual influence of pCO2 partial pressure, temperature, ionic strength (or salinity), major components and known calcite inhibitors (Mg, SO4, dissolved organic matter) in the complex calcite formation process under pertinent geological CO2 sequestration conditions. An inversion model of experimental kinetic rate data has been developped to link the precipitation rate of calcite of the independent variables and physico-chimal parameters. Using a multidimensional least squares regression method we generate a general multivariable equation of the form: dobs = G.m Where dobs is the column matrix representing the experimental precipitation rates (in the logarithm scale) and G is a matrix containing all the experimental parameter values (temperature, pCO2, activity of inhibitor and accelerators, ionic strength). The m term is also a column matrix corresponding to the value (weight) affected by each parameter and evaluated by the kinetic data inversion. Scenarios resulting from mixing of fluids in the aquifer and others enriched in CO2 show an rapid initial enhancement of the carbonate precipitation rate. However, when pCO2 and salinity decrease the calcite kinetic rate is inhibited and the rate is not ruled by simple affinity (i.e. [CO3]) laws. We observed an intermediate stage where the rate of calcite precipitation is low because of inhibiting influence of the salinity. In a final stage, the neutralisation of the fluid acidity by the rock dissolution generates a higher saturation state of the fluids that with a high carbonate ion concentration (from 0.90 to 2.5 mmol/kg) is responsible for 3 orders of magnitude increase of the calcite precipitation rate. Our results clearly identify the kinetics and thermodynamics role on the major parameters that drive the carbonate precipitation reaction.
U43C-1384
Experimental Fluid-Rock Reactions Along the CO2 Pathway in Carbonate Host Reservoir.
CO2 sequestration in geologic formations is increasingly being studied as a workable way for limiting CO2 overload in the atmosphere. Here, we will focus on carbonate rock which represents the large properties the targeted sedimentary reservoirs. The aim of this study is to produce experimental data base for constraining the modelling of CO2 injection and sequestration. A set of reactive percolation experiments in in-situ-like pressure and temperature conditions (i.e. T=100°C, P=12MPa) are presented. Experiments were designed to quantify reactions occurring near the CO2 injection zone where the aquifer fluid is saturated with CO2 and at increasing distances from the injection where the fluid is expected to contain progressively less CO2 and more divalent cations resulting from the rock dissolution along the fluid pathway. The underlying idea is to obtain experimental control points in space and time corresponding to the transport of the CO2 in the reservoir during the injection phase, whereas a complete and continuous reproduction of the processes at laboratory scale is obviously unfeasible. The protocol allows measuring changes in porosity and permeability continuously, as well as rock structure using recurrent X-ray microtomography imaging and effluent composition repeatedly. Results show that reactions produce high permeability channels, concomitant loss of integrity of the system close to the injection well, whereas precipitation inducing permeability decrease takes place far from the well. Mass transfers distribution and rate can be associated with the value of the CO2 partial pressure (PCO2) and Calcium saturation index (ICa) only. Specifically, dissolution is increasingly homogeneous as PCO2 decreases. Conversely, porosity-permeability relation is well fitted by the simple law k = a \; Φn where n can be related to the pore scale effective Damköhler number (which depend on the inlet PCO2 and ICa) by a simple power law relation. Then, the permeability change can be expressed as a function of the porosity changes by the relation k = a \; ΦbDa where a and b are constants that are probably fixed by the initial structure of the rock and the reaction type respectively.
U43C-1385
Design of Carbon Dioxide Storage in a North Sea Aquifer Using Streamline-based Simulation
We propose a carbon storage strategy where CO2 and brine are injected into an aquifer together followed by brine injection alone. This renders 80-95% of the CO2 immobile in pore-scale (10s micrometers) droplets in the porous rock; over thousands to billions of years the CO2 may dissolve or precipitate as carbonate, but it will not migrate upwards and so is effectively sequestered. The CO2 is trapped during the decades-long lifetime of the injection phase, reducing the need for extensive monitoring for centuries. The method does not rely on impermeable cap rock to contain the CO2; this is only a secondary containment for the small amount of remaining mobile gas. Furthermore, the favorable mobility ratio between injected and displaced fluids leads to a more uniform sweep of the aquifer leading to a higher storage efficiency than injecting CO2 alone. This design is demonstrated through the incorporation of a recent model of trapping and relative permeability hysteresis based on pore-scale modeling into a field-scale streamline-based simulator. One-dimensional results are verified through comparison with analytical solutions. Results are then shown for storage in a North Sea aquifer. We design injection to give optimal storage efficiency and to minimize the amount of water injected; for the case we study injecting CO2 with a fractional flow between 85 and 100% followed by a short period of chase brine injection gives the best performance.
U43C-1386
Enhancing the Ocean's Role in Carbon Dioxide Mitigation
Fossil fuels will likely remain the world's primary energy source for the foreseeable future. Practical, cost- effective, and safe means of significantly reducing fossil energy's CO2 footprint are therefore needed in order to avoid potentially catastrophic climate and environmental impacts. While considerable R&D effort is being invested in fossil fuel CO2 capture and storage above and below ground, the use of Earth's biggest single CO2 absorber and reservoir, the ocean, remains largely unexplored. For example, the US Department of Energy, lead agency in carbon management, has abandoned all ocean carbon research. This is risky and unwise because it forces global CO2 mitigation efforts to focus on only 30% of the earth's surface, ignoring most of the CO2 storage capacity of the planet. In addition to ocean storage of molecular CO2 that is captured from point sources on land, a variety of enhancements to natural marine biotic or abiotic CO2 uptake and sequestration have been proposed. These include increasing the chemical CO2 absorption of the ocean though the addition of alkalinity, or the addition of micro- or macro-nutrients to enhance photosynthetic CO2 uptake and storage. Potentially less impactful schemes include reacting CO2 with wet limestone to form calcium bicarbonate for subsequent ocean storage, or harvesting agricultural residue for long-term sequestration in anoxic ocean sediments. In many instances the cost/benefit of these approaches appear to be quite favorable, but further evaluation is needed, while additional ideas for ocean-based mitigation should be solicited. It is becoming clear that no one mitigation strategy will single-handedly stabilize atmospheric CO2, and the best strategies may ultimately bear little resemblance to those currently favored. Therefore, at this early stage we should not a priori ignore 70% of the earth's surface and a major component of the planet's carbon cycle in addressing the CO2 problem.
U43C-1387
Carbon Sequestration Through Ocean Iron Fertilization: A Proposed Large-scale Demonstration
Studies of the controls on ocean phytoplankton productivity during the 1980's and 1990's revealed that many areas of the open ocean have sufficient macronutrient (nitrate, phosphate, silicate) concentrations to support abundant phytoplankton growth, but have low concentrations of these primary producers that are responsible for about 45% of CO2 removed from the atmosphere each year. Laboratory and open ocean experiments have subsequently demonstrated that iron is a micronutrient that limits growth in many regions. Fertilization of the ocean with iron has been proposed as a mechanism for sequestering additional CO2 since it was understood to limit growth. Recent observation and modeling answers some of the questions that have been posed about the impact of such fertilization. Other questions about the efficacy and impact of fertilization require observation of a larger-scale demonstration. A large (250 x 250 km) fertilization demonstration is planned for 2008 that will include an array of measurements of carbon flux (sediment traps, Th- 234, carbon system parameters), phytoplankton assemblage, macronutrients and Fe, and greenhouse gases. Although privately funded, all data will be available to the scientific community following the cruise.
U43C-1388
Geologic Carbon Sequestration in a Lightly Explored Basin: the Puget-Willamette Lowland
The Puget-Willamette Lowland is located between the Cascade Range and Olympic Mountains-Coast Range. Exploration for oil and gas there commenced in 1890. Over 700 wells subsequently drilled yield one commercial gas discovery. Eocene sediments deposited west of an ancestral Cascade Range include a coal-bearing sequence covering much of the Puget-Willamette Lowland. The terrestrial deposits pass into marine deposits to the west. Syn- depositional normal faulting and strike-slip faulting are evident in several sub-basins. In the southern Lowland, normal faults were modified by episodes of late Eocene and Miocene transpression, which resulted in mild inversion of older normal faults Preserved sediments indicate that local subsidence continued into Miocene- Pliocene time, and was followed in the northern Lowland by extensive Pleistocene glaciation. In the northern Lowland, Holocene faulting is recognized in outcrop and is interpreted on seismic data acquired in Puget Sound. Structures formed by early Miocene or earlier events may have trapped migrating hydrocarbons. Structures formed or modified by Holocene faulting very probably post-date hydrocarbon generation and migration. The region appears to host potential geologic sequestration targets, including coals, sandstones, and vesicular basalt flows. The size and location of potential traps is poorly constrained by present data. Experience in better explored fore arc basins suggests 10 to 30 percent of the basin may be deformed into suitable trapping geometries. Modern seismic data is required to identify potential sequestration traps. More than one well will be required to confirm the presence and size of these traps. The present boom in oil and gas drilling has created a robust environment for seismic and drilling companies, who command unprecedented rates for their services. Only one seismic crew is presently active on the West Coast, and only a few exploration drilling rigs are available. If this environment persists, then sequestration efforts will compete directly with the hydrocarbon industry for these services, leading to higher service company prices as well as delayed schedules. Carbon sequestration policy thus entails financial incentives that allow geologic sequestration projects to compete for exploration services.
U43C-1389
Formation Dry-out and Salt Precipitation During Injection of CO2 into Saline Aquifers
Injection of CO2 into a saline aquifer may cause formation dry-out and precipitation of salt near the injection well, which may reduce formation porosity, permeability, and injectivity. This paper uses numerical simulation to explore the role of different processes and parameters in the salt precipitation process, and to examine injection strategies that could mitigate the effects. The main physical mechanisms affecting the dry-out and salt precipitation process include (1) displacement of brine away from the injection well by injected CO2, (2) evaporation of brine into the flowing CO2 stream, (3) upflow of CO2 due to gravity effects (buoyancy), (4) backflow of brine towards the injection point due to capillary pressure gradients that oppose the pressure gradient in the CO2-rich ("gas") phase, and (5) molecular diffusion of dissolved salt. The different mechanisms operate on a range of spatial scales. Simulations in 1-D radial geometry are conducted to resolve multi-scale processes by taking advantage of the similarity property, i.e., the evolution of system conditions as a function of radial distance R and time t depends only on the similarity variable R*R/t. Simulations in 2-D vertical cross sections are used to examine the role of gravity effects. We find that counterflow of CO2 and brine can greatly increase aqueous phase salinity, and can promote substantial salt precipitation even in formations with low dissolved solids. Salt precipitation can accentuate effects of gravity override. We also evaluate the efficacy of injecting a slug of fresh water prior to commencement of CO2 injection, as a means of reducing salt precipitation near the injection well. This work was supported by the Zero Emission Research and Technology project (ZERT) under Contract No. DE- AC02-05CH11231 with the U.S. Department of Energy.
U43C-1390
Dependence of CO2-Brine Interfacial Tension on Aquifer Pressure, Temperature and Water Salinity
Carbon dioxide storage in deep saline aquifers is a climate-change mitigation strategy that has significant potential in the short-to-medium term. The displacement of formation water by CO2 (drainage) and of CO2 by invading aquifer brine (imbibition) depend on the interfacial tension (IFT) of the CO2-brine system. To provide needed data, an extensive laboratory program was conducted for the measurement of the interfacial tension between CO2 and water or brine covering the ranges of 2 to 27 MPa pressure, 20°C to 125°C temperature, and 0 to 334,000 mg/l water salinity. The laboratory experiments were conducted using the pendant drop method combined with the Laplace solution for the profile of the brine drop in the CO2-rich environment. The analysis of the resulting set of 294 IFT measurements reveals that: 1) for conditions of constant temperature and water salinity, IFT decreases steeply with increasing pressure in the range P<Pc, and mildly for P>Pc, with an asymptotic trend towards a constant value for high pressures; 2) for the same conditions of constant pressure and temperature, IFT increases with increasing water salinity, reflecting decreasing CO2 solubility in brine as salinity increases; 3) the dependence of IFT on temperature is more complex, depending on the CO2 phase. For T<Tc, IFT increases with increasing temperature, around the critical temperature (Tc) IFT decreases significantly (dips), and then increases again with increasing temperature for T>Tc, with an asymptotic trend towards a constant value for high temperatures. These results indicate that, in the case of CO2 storage in deep saline aquifers, the formation water displacement by injected CO2 during the injection phase of CO2 storage and the CO2 displacement by invading brine during the CO2 migration phase depend on the in-situ conditions of pressure, temperature and water salinity through the effects that these primary variables have on the IFT between CO2 and aquifer brine. Since the IFT of CO2-brine systems affects relative permeability and capillary pressure, it is essential that the in-situ conditions and their effect of secondary variables are properly taken into account when evaluating the fate of the injected CO2 in deep saline aquifers.
U43C-1391
Isotope tracing of CO2 Seepage: Results from Controlled Release Experiment in Bozeman, Montana, USA
The geological storage of carbon dioxide (CO2) captured from the emissions of combustion of fossil fuels is a promising option to mitigate the increase in atmospheric greenhouse gases. Within the past 5 years, efforts in understanding the storage capacity, chemical and physical alteration, and the leak potential of CO2 impact to various reservoir types have been researched both at the laboratory and field. State-of-the-art monitoring equipment and models in the areas of geophysics, geochemistry, atmospheric chemistry, and remote sensing are being employed within this research area. Specifically, over the past 2 years, a controlled field experiment has taken place in Bozeman, Montana where pure CO2 has been released at known rates and depths to quantify the detection limits of various monitoring techniques for the use of CO2 seepage detection. In 2006, CO2 was injected at 0.1 ton/day for 10 days at 2.5 m depth through a vertical well, and in 2007, CO2 was injected at 0.1 ton/day for 10 days at an average of 2 m depth through a horizontal well. The monitoring tool highlighted in this paper, is the use of stable isotope detection of CO2 seepage into atmospheric, vegetation, and groundwater reservoirs. Preliminary results show a distinct isotopic impact to the local groundwater (at 1.2 m depth) and surface CO2 (as measured with closed surface chambers) within 24 hours after CO2 was injected. Plume development and dispersion as well as quantification of seepage CO2 versus natural CO2 are discussed.
U43C-1392
Carbon sequestration and eruption hazards
In order to reduce the buildup of carbon dioxide in the atmosphere, proposals have been made to sequestrate carbon in ocean, or in coal mines and other underground formations. High gas concentration in ocean or underground formations has to potential to power gas-driven eruptions. In this presentation, possible eruption hazards are explored. Whenever carbon dioxide is sequestrated in the form of carbon dioxide gas, or dissolved and/or absorbed carbon dioxide, it is necessary to exercise caution to avoid gas-driven eruption hazard. It is long known that explosive volcanic eruptions are driven by H2O gas in magma. Lake eruptions powered by dissolved CO2 in lake bottom water were discovered in the 1980's (Kling et al., 1987; Zhang, 1996). Gas-driven ocean eruptions with mechanism similar to lake eruptions have been hypothesized (Zhang, 2003; Zhang and Kling, 2006) although not confirmed. Mud volcanos are commonly thought to be driven by methane-rich fluids in sediment (Milkov, 2000). Recently, Zhang et al. (2007) have proposed that coal outbursts in underground coal mines are driven by dissolved high CO2 concentration in coal, causing coal fragmentation and outburst. That is, coal outbursts may be regarded as a new type of gas-driven eruptions. Therefore, high concentrations of free gas or dissolved/absorbed gas may power eruptions of magma, lake water, ocean water, sediment, and coal. Gas- driven volcanic, lake and ocean eruptions are due to volume expansion from bubble growth, whereas gas-driven coal and sediment eruptions are due to high gas-pressure, leading to fragmentation of coal and sediment. (In explosive volcanism, magma fragmentation is also a critical point.) The threshold conditions for many of these eruptions are not known yet. In planning large (industrial) scale injection of CO2 into a natural reservoir, it is important to know the eruption threshold and design the injection scheme accordingly. More safe sequestration in terms of eruption hazards would utilize chemical reactions to immobilize gaseous CO2 into carbonates. References Kling G.W. et al. (1987) Science 236, 169-175. Zhang Y. (1996) Nature 379, 57-59. Zhang Y. (2003) Geophys. Res. Lett. 30(7), (51-1)-(51-4), doi 10.1029/2002GL016658. Zhang Y., Kling G.W. (2006) Annu. Rev. Earth Planet. Sci. 34, 293-324. Zhang Y., Guan P., Wang H. (2007) 6th IPACES meeting abstract, 26-29 June 2007, Wuhan, China.
U43C-1393
Analytical Model for Screening Potential Repositories for Subsurface Sequestration of CO2
We have developed a screening tool for assessing the suitability of candidate repositories for subsurface carbon dioxide (CO2) sequestration, using a combination of easy-to-use analytical equations. We considered the injection of CO2 at a constant rate into a confined homogeneous deep saline aquifer via a single vertical well. The analytical equations give predictions of (1) the location of the CO2-brine interface, (2) temporal and spatial variations of pressure in the formation, and (3) temporal pressure changes at the injection well. By estimating these few parameters, it may be possible to determine if a candidate repository is viable. We demonstrate the validity of the analytical model through comparison with the TOUGH2 numerical model. The formation conditions and assumptions in TOUGH2 were set similar to those of the analytical model. Estimates of fluid saturation and pressure profiles show excellent agreement between the two models. The analytical model neglects changes in fluid properties due to changes in pressure, but simulations in TOUGH2 indicate that little error is introduced by this simplification. Comparison with TOUGH2 also enables us to determine the likely importance of other assumptions or simplifications invoked in the analytical model. Generally, the analytical model predicts a slightly higher pressure and plume extent than the numerical model, but the differences are small. Therefore, the easy-to-use analytical model may be a suitably accurate and conservative tool for regulatory or screening use in assessing candidate CO2 repositories.
U43C-1394
Tropical Wetlands as Carbon Sinks
This presentation focuses on the tropical wetlands of sub-Saharan Africa. These are an understudied ecosystem in which large emergent grasses and sedges normally dominate and which have the potential to sequester significant amounts of carbon. Measurements of Net Primary Production of these wetlands show that they are some of the highest values recorded for any ecosystem. We have used eddy covariance to measure Net Ecosystem Exchange of pristine and disturbed wetlands and show that pristine systems can have sink strengths as strong as tropical forests while disturbed systems that have been reclaimed for agricultural purposes have a very much reduced carbon sink activity and may be net carbon sources. The management issues surrounding the use of these wetlands illustrate a direct conflict between the production of food crops for the local population and the maintenance of carbon sequestration as an ecosystem service.
U43C-1395
The potential for carbon storage in UK peatlands
Peatlands are the UK's largest single terrestrial carbon store with carbon stored in UK peatlands than in forests of Britain and France combined, further this amount of carbon is equivalent to 35 years of total UK CO2 output. Unlike most northern peatlands in the peat soils of the UK are heavily managed for recreation and agriculture and due to their proximity to major centres of population are under more anthropogenic pressure than most peatlands. However recent studies have shown several crucial pieces of evidence that may suggest that the carbon storage of these managed peatlands in not being realised: i) A complete carbon budget of a pristince peat catchment overa 13 year period shows that on average it is a net carbon store of 60 Mg C/km2/yr, but that in some years this net sink of carbon could be close to neutral. ii) Complete carbon budgets of managed peat catchments shows that can be net sources of carbon of upto 100 Mg C/km2/yr This means that if a managed peatland could be restored to the same condition as a "pristine" peatland there could be as much as 160 Mg C/km2/yr additional storage in this ecosystem. If this could be achieved for all the peatlands in the UK the amount of additional carbon storage would be equivalent to 2% of the UK road traffic. Further, at the current price of carbon on voluntary offsetting markets this would represent a profit over restoration costs of upto £1.5 billion over 20 years. This study has used field studies and regional models to explore the carbon potential of peatlands
U43C-1396
Microbial Response to Carbon Dioxide Injection in a Shallow Aquifer
Extensive research is underway to investigate the geophysical and geochemical dynamics of subsurface carbon sequestration, but there has been only theoretical consideration of the microbial response. Microbial dynamics are capable of altering the range and rates of geochemical reactions in the subsurface. The goal of this field experiment is to link geochemical changes due to CO2 injection to alterations in the microbial community and to provide an initial characterization of the microbial response. A seven week push-pull experiment was conducted at the Lamont-Doherty Earth Observatory Test Well. 200L of groundwater was extracted, bubbled with carbon dioxide, augmented with a bromide tracer, and injected to 230m depth below ground surface. The hydraulically isolated injection zone marked the contact area between dolerite sill and sedimentary rock. Samples were taken on a weekly basis. Geochemically, a drop in pH from 9.4 to 4.5 at injection was coupled with a release of Fe2+ from the formation. As neutralization and mixing caused pH to return toward background levels, Fe2+ concentrations decreased. The aquifer remained anoxic throughout the experiment. DNA was successfully extracted and the gene encoding 16S ribosomal RNA was amplified from all samples with the exception of the injection fluid. Sequencing from clone libraries and tRFLP analyses were used to characterize microbial dynamics during the seven week study. Whereas the number of microbial groups detected remained relatively constant over the course of the experiment, changes were observed in both the dominant microbes phylogenetic identity and relative abundance. Methane concentrations increased from background levels (below 50 nM) to 4.2 nM after injection, but initial attempts to amplify archaeal and methanogen-specific genes were unsuccessful, bringing into question the presence of a significant methanogenic population. These results confirm that there is a microbial response to carbon dioxide injection and indicate the importance of further research regarding microbial implications for carbon sequestration strategies.
U43C-1397
Biofilm enhanced subsurface sequestration of supercritical CO2
In order to develop subsurface CO2 storage as a viable engineered mechanism to reduce concentrations of atmospheric CO2, any potential ¡°leakage" of injected supercritical CO2 (scCO2) from the ground to the atmosphere must be reduced. Here, we investigate the utility of biofilms, which are microorganism assemblages firmly attached to a surface, as a means of reducing scCO2 leakage. Firstly, experiments were performed to test whether biofilms were more resilient than planctonic cells to scCO2. Bacillus mojavensis biofilms were grown on a sand support matrix in scCO2 extractor cartridges at 30°C. B. mojavensis was also grown under suspended planctonic conditions in the same media overnight and aliquots were decanted into scCO2 extractor cartridges. Biofilm and suspended B. mojavensis samples were processed on a Supercritical Fluid Extractor with pressurization to 2000 psi at 35°C, and a 20 minute flow of scCO2. Suspended growth samples revealed a 3 log reduction in cell viability while biofilm only showed a 1 log reduction, demonstrating that B. mojavensis biofilms are more resilient than planctonic cells to scCO2. Protective extra cellular polymeric substances which make up the biofilm matrix likely provide a protective barrier against scCO2. Secondly, the ability of biofilms to grow under high pressure and reduce the permeability of porous geological matrices was investigated using a unique high pressure (8.9MPa), moderate temperature (¡Ý 32°C) flow reactor containing 40 millidarcy Berea sandstone cores. The flow reactor was inoculated with the biofilm forming organism Shewanella fridgidimarina. Electron microscopy of the rock core revealed substantial biofilm accumulation in rock pores which resulted in <99% reduction in core permeability. Permeability did not increase in response to starvation and scCO2 challenges. Viable population assays of organisms in the effluent indicated survival of the microorganisms following scCO2 challenges of <71h and starvation for <363h. Biofilms are more resilient to scCO2 than planctonic cells, display continued viability under high pressure, and are able to significantly reduce porous media permeability under high pressure. This is extremely encouraging for the prospective use of engineered biofilm barriers for controlling leakage of geologically sequestered CO2.
U43C-1398
Impact of Wellbore Cement Degradation on CO2 Storage Integrity
The sequestration of CO2 in underground geologic formations requires a thorough evaluation of potential leakage of the sequestered CO2 through the numerous existing wellbores which penetrate them. Leakage rates of less than 1% per 100 years have been deemed necessary for geologic sequestration to be viable. Well bores are of particular interest because the cement used to line and/or plug the well, may be vulnerable to acid attack. Injected CO2 will dissolve, becoming carbonic acid, which can readily react with calcium hydroxide and calcium silicate hydrate, key components in hardened cement. Laboratory experiments have been performed in order to determine the physical and chemical changes, as well as the rate of degradation of the cement under simulated sequestration reservoir conditions, including both aqueous and supercritical CO2. Upon exposure to aqueous CO2, hardened cement formed well-defined reaction zones by a 2-step process. The first step is the dissolution of Ca(OH) 2 (s) and subsequent precipitation of CaCO3 (s). The formation of CaCO3 (s) has been reported to decrease cement permeability and increase its compressive strength. The second step is the dissolution of CaCO3 (s) resulting in a leaching of calcium from the cement matrix. The resulting cement paste has a significant increase in porosity, is primarily composed of amorphous silica gel, and lacks structural integrity. Although it is clear that cement is degraded, the results of this study suggest that the reactions involved are slow. In fact, long term experiments show that the rate of degradation decreases over time, likely due to the precipitation of CaCO3 (s) within the pore space of the cement. This phenomenon should limit the negative impact that chemical degradation will have on well bores. Supercritical CO2 exposure (saturated with water vapor) led to a very different process by which CaCO3 (s) was deposited throughout the matrix and on the surface, rather than within an isolated reaction zone. Over the one-year time period of the experiments, this condition led to a smaller amount of total degradation than in the aqueous phase. However, in this case, there was no deceleration of the reaction observed. It is unlikely that the diffusion controlled degradation process observed in these experiments would lead to well failure in well completions that are well cemented with neat Portland cement (without additives). Further investigation is required to evaluate the effect of cement additives, fractures or channels in the cement, and geomechanical stress.
U43C-1399
Leveraging Characterization Data to Develop a Comprehensive Monitoring Plan for CO2 Storage at an Industrial Injection Site
In the current validation stage of geologic storage technology, the development of a monitoring, mitigation and verification (MMV) plan for an industrial carbon sequestration project requires consideration of both the implementation and research goals, within the practical site constraints. In this presentation, we integrate data from the drilling of a characterization well and 2D surface seismic to develop an MMV plan for the proposed injection and monitoring phase at AEP's Mountaineer Power Plant in New Haven, West Virginia. The Mountaineer plant has specific challenges for MMV design such as the presence of the Ohio River, relatively rough terrain and injection targets of varying thickness. In addition, there is limited space at the surface so any monitoring must be carefully designed to best utilize the area. For example, we present our evaluation the applicability of seismic monitoring techniques. This includes the possibility of using crosswell seismic or vertical seismic profiling to help reduce signal attenuation at the surface and increase resolution to allow the imaging of smaller units within the injection reservoir. Also, we evaluate using downhole, point measurements such as reservoir fluid sampling and other wireline tools in monitoring wells. The use of these tools may be the key element in evaluating dissolution and reservoir behavior. This results in an MMV plan that allows for plume location identification and reservoir assessment while keeping costs realistic for an industrial site. This work is supported by DOE-NETL, AEP, Ohio Coal Development Office, BP, Battelle, and Schlumberger.
U43C-1400
Laboratory and Simulation Investigation of Gas Adsorption, Transport, and Carbon Sequestration in Coal
Deep coalbeds are attractive for sequestering CO2. Injection of CO2, or mixtures of CO2 and N2, enhances CH4 recovery from the coalbed and at the same time sequesters CO2. Powder River Basin (WY) coals, as studied here, adsorb about three times as much CO2 as CH4. Thus, sequestration in coalbeds has the potential for carbon neutrality. We study gas flow and adsorption within coal using experiments and numerical modeling. Coal samples are characterized by porosity, CH4/ CO2/ N2 sorption isotherms, and permeability. This coal exhibits significant hysteresis among adsorption and desorption isotherms. Coal permeability is a function of the injected gas composition, pore pressure (at constant effective stress), and pressure history. Displacement experiments are conducted with N2, CO2, and various mixtures of CH4, CO2 and N2. Most interestingly, the coal exhibited ability to separate N2 from CO2 due to the preferential strong adsorption of CO2. Injection of a mixture rich in CO2 gives slower initial recovery of CH4, increases breakthrough time, and decreases the volume of gas needed to sweep out the coalbed. Injection gas rich in N2 leads to faster recovery of CH4, earlier breakthrough of N2, and a significant fraction of N2 in the produced gas in short time. We develop a two-phase (gas and solid), dual continuum model to rationalize and explain the experimental trends. The dynamics of gas movement through coal are determined in large part by the sorption behavior of mixtures of CH4, CO2 and N2 on the coal surface. These ternary gas mixtures are best described by a real adsorbate solution model in comparison to the commonly used extended Langmuir equation. According to the multicomponent adsorption isotherms, sorption and the selectivity of a particular gas species for a coal surface is a function of pressure and the mixed-gas composition. Reproduction of transient binary flow behavior is characterized as excellent and the dynamics of ternary systems are predicted with acceptable accuracy. For these coals, the most sensitive simulation input parameter was the multicomponent sorption isotherms, including scanning loops. On a practical note, accurate tools for performance prediction in coalbeds are instrumental in design and implementation of sequestration schemes. The results and analysis garnered demonstrate that models substantially more sophisticated than the state of the art are needed when mixtures of CO2 and N2 are injected into coalbeds containing CH4.
U43C-1401
Numerical modeling of CO2 storage in gob areas of coal mines
CO2 storage in coal mines can offer a remarkable contribution to world-wide greenhouse gas control. Therefore, numerous technical approaches of CO2 storage in coal mines especially considering sorptive storage on residual coal seams have been developed within the last decade. The CO2 storage concept discussed here considers the utilization of mining wastes from coal processing as CO2 adsorbent resulting from their high content of organic matter. For that purpose a sorption reactor at the surface is used to capture CO2 from flue gas originated by industrial combustion processes. CO2 is separated from N2 in that reactor, and a CO2 mining waste suspension is established, involving a water content applicable for its pumping. The suspension is subsequently injected into remaining gob areas behind longwall workings providing efficient CO2 storage accompanied by subsidence mitigation and underground mining waste disposal. The main aspect with respect to storage security is potential CO2 outgassing from stowed gob areas into the longwall face as well as adjacent drifts and workings. A software package for numerical simulation of multi- component flow and transport in porous media (MUFTE_UG) is used to investigate the interaction of gas flow parameters in terms of quantity, time and space. Different CO2 storage scenarios are taken into account by the application of a parameterization based on laboratory experiments as well as knowledge and experience of German mining and mining research companies. The low permeability of the mining wastes is the main criterion preventing CO2 flow out of the stowed gob areas. Furthermore, the load of the roof compresses the injected CO2 mining waste suspension leading to a consequent reduction of parameters like porosity and permeability. Therefore, implementation of a model considering CO2 outgassing from stowed gob areas and a subsequent sensitivity analysis are conducted to evaluate interacting model parameters by their relevance and the overall CO2 storage risks resulting from the application of the described sorptive CO2 storage technology. http://www.co2trap.org
U43C-1402
QUANTITATIVE SOIL CARBON ANALYSIS WITH IN SITU LASER-INDUCED BREAKDOWN SPECTROSCOPY BY MULTIVARIATE ANALYSIS
The Earth's oceans, forests, agricultural lands and other natural areas absorb about half of the carbon dioxide emitted from anthropogenic sources. Terrestrial carbon sequestration strategies are immediately available to bridge the gap between current terrestrial sequestration capacity and high-capacity geologic sequestration projects available in 10 to 20 years. Terrestrial carbon sequestration strategies consist of implementing land management practices aimed at decreasing CO2 emitted into the atmosphere and developing advanced measurement tools to inventory and monitor carbon processes in soils and biota. Laser-Induced Breakdown Spectroscopy (LIBS) is one of the analytical tools used to determine the total soil carbon in samples within the Big Sky and Southwest Carbon Sequestration Regional Partnerships. LIBS involves focusing a Nd:YAG laser operating at 1064nm onto the surface of the sample. The laser ablates material from the surface, generating an expanding plasma containing electronically excited ions, atoms, and small molecules. As these electronically excited species relax back to the ground state, they emit light at wavelengths characteristic of the species present in the sample. Some of this emission is directed into one of three dispersive spectrometers. The experiments discussed in this paper were completed with a person portable LIBS instrument designed and built at Los Alamos National Laboratory that uses a Kigre Laser (25mJ/pulse) and an Ocean Optics HR2000 dispersive spectrometer. This instrument was used to probe samples collected from Illinois (no-till loam), Michigan (no-till clay), and North Dakota (reduced-till sand). A new multivariate analysis technique was employed to extract concentrations to 0.5%C with significantly greater statistical accuracy than conventional univariate techniques. These MVA techniques appear to completely compensate for these matrix effects because the analysis identifies the correlations between the spectra (independent variables), the individual elements of interest (dependent variables such as Si) as well as the other elements in the matrix.
U43C-1403
Effects of Carbon Depth Profile on INS Measurement
Inelastic Neutron Scattering (INS) is a new system for measuring carbon in soil in situ that is non-destructive. In addition the INS can be used in stationary or scanning modes of operation enabling type of measurements not possible till now. It is based on counting 4.44 MeV characteristic gamma rays emitted from carbon nuclei undergoing inelastic neutron scattering with fast, 14 MeV, neutrons. Because of the attenuation of the neutrons, on their way in, and of the gamma rays, on their way out, the large volume of about 0.3 m3 sampled by the INS system causes it to respond preferentially to carbon atoms located near the surface. Thus, the carbon signal depends on the variations in the carbon depth profile; however, this dependence is reduced by an averaging process resulting from the large footprint of about 1 m2 of the INS system. The encountered variability in the depth profiles on small 30 cm scale and on large field size scale is presented for various fields. We also show results of Monte Carlo simulations of the INS response to various carbon depth profiles. Experimentally we show that depending on the field conditions, i.e. profound variability in the carbon depth profile or extensive changes in the carbon distribution in the field, the scanning results with the INS system may differ from the mean value calculated from few INS discrete stationary measurements. Since the static measurements are analogous to conventional chemical analysis using soil cores, it raises the question which type of measurement is more representative of the field carbon content; the discrete chemical analysis using geostatistical considerations or continuous field scanning made possible with the INS system. Clearly the new INS methodology introduces novel capabilities for soil carbon analysis not possible with the conventional approach of dry combustion. The advantages and pitfalls of the INS system with the need to defining practical new calibration concepts for it are discussed in the forthcoming presentation.
U43C-1404
Simulated in situ Determination of Soil Profile Organic and Inorganic Carbon Using Combined VisNIR and LIBS Sensors
There is growing need for rapid, accurate, and inexpensive methods to measure, and verify soil organic carbon (SOC) change for national greenhouse gas accounting and the development of a soil carbon trading market. Visible and Near Infrared Spectroscopy (VisNIR) and Laser Induced Breakdown Spectroscopy (LIBS) techniques have the potential to fill that need. LIBS and VisNIR are fundamentally different and complementary technologies. LIBS provides precise elemental analysis of soils, but cannot distinguish between organic C and inorganic C. VisNIR has been used to characterize soil mineral and molecular composition and can distinguish between organic C and inorganic C. In this study we evaluated the precision of a simulated in situ VisNIR/LIBS proximal sensing array for soil profile carbon measurement. We simulated the in situ system by scanning 120 intact soil cores (3.8 cm x 50 cm) from three agricultural fields in north central Montana, USA. VisNIR measurements were taken using an Analytical Spectral Devices (ASD, Boulder, CO, USA) Agrispec spectrometer. LIBS measurements involved focusing a Nd:YAG laser onto the surface of the soil core to produce a plasma. The spectra from emitted plasma light were detected with a charge- coupled device. LIBS and VisNIR measurements were taken concurrently at 5 cm increments along each intact soil core. Subsamples of soil ({~} 4 g) were taken from interrogation points, and then each core was cut into 10 cm increments for carbon analysis. A representative subset (192 samples) of the interrogation point samples were used to calibrate and validate several VisNIR/LIBS models to compare VisNIR /LIBS vs. standard organic and inorganic carbon analysis.
U43C-1405
Soil Organic Carbon Estimation and Mapping Using "on-the-go" VisNIR Spectroscopy
Soil organic carbon (SOC) and other soil properties related to carbon sequestration (eg. soil clay content and mineralogy) vary spatially across landscapes. To cost effectively capture this variability, new technologies, such as Visible and Near Infrared (VisNIR) spectroscopy, have been applied to soils for rapid, accurate, and inexpensive estimation of SOC and other soil properties. For this study, we evaluated an "on the go" VisNIR sensor developed by Veris Technologies, Inc. (Salinas, KS) for mapping SOC, soil clay content and mineralogy. The Veris spectrometer spanned 350 to 2224 nm with 8 nm spectral resolution, and 25 spectra were integrated every 2 seconds resulting in 3 -5 m scanning distances on the ground. The unit was mounted to a mobile sensor platform pulled by a tractor, and scanned soils at an average depth of 10 cm through a quartz-sapphire window. We scanned eight 16.2 ha (40 ac) wheat fields in north central Montana (USA), with 15 m transect intervals. Using random sampling with spatial inhibition, 100 soil samples from 0-10 cm depths were extracted along scanned transects from each field and were analyzed for SOC. Neat, sieved (<2 mm) soil sample materials were also scanned in the lab using an Analytical Spectral Devices (ASD, Boulder, CO, USA) Fieldspec Pro FR spectroradiometer with a spectral range of 350-2500 and spectral resolution of 2-10 nm. The analyzed samples were used to calibrate and validate a number of partial least squares regression (PLSR) VisNIR models to compare on-the-go scanning vs. higher spectral resolution laboratory spectroscopy vs. standard SOC measurement methods.
U43C-1406
Physical and Economic Integration of Carbon Capture Methods with Sequestration Sinks
Currently there are several different carbon capture technologies either available or in active development for coal- fired power plants. Each approach has different advantages, limitations and costs that must be integrated with the method of sequestration and the physiochemical properties of carbon dioxide to evaluate which approach is most cost effective. For large volume point sources such as coal-fired power stations, the only viable sequestration sinks are either oceanic or geological in nature. However, the carbon processes and systems under consideration produce carbon dioxide at a variety of pressure and temperature conditions that must be made compatible with the sinks. Integration of all these factors provides a basis for meaningful economic comparisons between the alternatives. The high degree of compatibility between carbon dioxide produced by integrated gasification combined cycle technology and geological sequestration conditions makes it apparent that this coupling currently holds the advantage. Using a basis that includes complete source-to-sink sequestration costs, the relative cost benefit of pre-combustion IGCC compared to other post-combustion methods is on the order of 30%. Additional economic benefits arising from enhanced oil recovery revenues and potential sequestration credits further improve this coupling.
U43C-1407
Current Status of Legislative Proposals on Greenhouse Gas Emissions and Alternative Energy in the U.S. Congress
The 110th Congress is now beginning to grapple with the issue of human-induced climate change and what, if anything, to do about it. A number of bills are currently being considered that would limit greenhouse gas emissions using various policy mechanisms and over various time frames. With a commitment by the current Congressional leadership to pass legislation addressing global warming, and significant hurdles remaining, it promises to be an eventful fall session. I will review the current status of these legislative proposals and their prospects of becoming law.
U43C-1408
Toward an effective governance regime for geologic carbon storage
Carbon capture and storage (CCS) technology is currently poised to play a significant role in mitigating CO2 emissions from future fossil fuel combustion, especially from coal-fired power plants, which are expected to rapidly increase in number over the next several decades. At the same time, large-scale deployment of CCS continues to be impeded by concerns about the long-term integrity of geologic storage reservoirs. In this study, we apply established concepts of learning-by-doing to the problem of reservoir leakage. Our results suggest that when learning is present, traditional measures of (initial) reservoir integrity do not sufficiently capture the time- integrated behavior of the system that is most relevant to the global CO2 problem. In one formulation, we find that when learning is explicitly incorporated into a reservoir model, total leakage is always finite and scales approximately quadratically with the learning time constant and inversely with the initial retention time constant. To highlight the policy relevance of this study, we consider the implications of these results for the larger site licensing process. We expect that an upper bound on total allowable leakage will be decided by policymakers. Armed with this number and some informed, expert-driven judgments about the rate at which learning will proceed, a regulator could use our model, or a more sophisticated variant, to calculate an upper bound on the maximum initial leakage rate. This criterion would then be one of several prerequisites to certification. The entire process could be amended over time as new data is made available. We hope that our model will provide a platform for scholars from different fields to engage one another and to work toward an acceptable, compelling and long-lasting management framework for CCS.
U43C-1409
Policy Needs for Carbon Capture & Storage
Climate change is one of the most pressing environmental problems of our time. The widespread consensus that exists on climate science requires deep cuts in greenhouse gas emissions, on the order of 50-80% globally from current levels. Reducing energy demand, increasing energy efficiency and sourcing our energy from renewable sources will, and should, play a key role in achieving these cuts. Fossil fuels however are abundant, relatively inexpensive, and still make up the backbone of our energy system. Phasing out fossil fuel use will be a gradual process, and is likely to take far longer than the timeframe dictated by climate science for reducing emissions. A reliable way of decarbonizing the use of fossil fuels is needed. Carbon capture and storage (CCS) has already proven to be a technology that can safely and effectively accomplish this task. The technological know-how and the underground capacity exist to store billions of tons of carbon dioxide in mature oil and gas fields, and deep saline formations. Three large international commercial projects and several other applications have proved this, but substantial barriers remain to be overcome before CCS becomes the technology of choice in all major emitting sectors. Government has a significant role to play in surmounting these barriers. Without mandatory limits on greenhouse gas emissions and a price on carbon, CCS is likely to linger in the background. The expected initial carbon price levels and their potential volatility under such a scheme dictates that further policies be used in the early years in order for CCS to be implemented. Such policies could include a new source performance standard for power plants, and a low carbon generation obligation that would relieve first movers by spreading the additional cost of the technology over entire sectors. A tax credit for capturing and permanently sequestering anthropogenic CO2 would aid project economics. Assistance in the form of loan guarantees for components of the technology that make financing problematic due to insufficient performance guarantees would help first movers. The development of a pipeline network for transporting CO2 will require centralized planning in order to materialize and make use of economies of scale. The federal government should significantly accelerate its research, development and demonstration program, with particular emphasis on multi-megaton injections in representative geological settings. Finally, a comprehensive regulatory framework for large-scale injections is a high priority item that can and should be developed now, with scope for revision after our experience with CCS projects grows.
U43C-1410
A Policy Option To Provide Sufficient Funding For Massive-Scale Sequestration of CO2
Global emissions of CO2 now are nearly 30 billion tons per year, and are growing rapidly due to strong economic growth. Atmospheric levels of CO2 have reached 380 ppm and recent reports suggest the rate of increase has gone from 1% per year in the 1990's to 3% per year now – with potential to cross 550ppm in the 2020 decade. Without stabilization of atmospheric CO2 below 550ppm, climate models predict unacceptably higher average temperatures with significant risk of runaway global warming this century. While there is much talk about reducing CO2 emissions by switching to non-fossil energy sources, imposing energy efficiency, and a host of other changes, there are no new large-scale energy sources on the horizon. The options are to impose draconian cuts in fossil energy consumption that will keep us below 550ppm (devastating the global economy) – or to adopt massive-scale sequestration of CO2. Three approaches are feasible: biological ocean sequestration, geologic sequestration, and biological terrestrial sequestration. Biological sequestration is applicable to all CO2 sources, whereas geologic sequestration is limited to fossil-fuel power plants and some large point-source emitters such as cement plants and large industrial facilities. Sequestration provides a direct mechanism for reducing atmospheric levels of CO2, whereas offsetting technologies such as wind power or improved efficiency, reduce the need for more fossil fuels but do not physically remove CO2 from the environment. The primary geologic technique, carbon capture & sequestration (CCS), prevents CO2 from entering the atmosphere but likewise does not reduce existing levels of atmospheric CO2. Biological sequestration (ocean or terrestrial) physically removes CO2 from the atmosphere. Since we cannot shut down our global economy, urgent action is needed to counteract CO2 emissions, and avoid catastrophic climate change. Given the long lead time and/or small impact of offsetting energy sources, sequestration is the only way to achieve near and medium-term reductions in atmospheric CO2 levels. To finance massive-scale sequestration of CO2, we propose the World Trade Organization (WTO) become an active player in the sequestration market. Given the WTO's role as overseer of international trade agreements annually representing $30 trillion in imports and exports of goods and services, it is by far the largest global economic force and therefore offers the broadest economic base. Absent a real solution to CO2 emissions, the global economy - and world trade - will shrink dramatically. The WTO can jumpstart the market for CO2 sequestration by issuing long term contracts to purchase bona fide sequestration-derived CO2 credits. Under this proposal, an initial price of $100 per ton which steps-down by 5% per year could bring forth the sequestration investment needed to achieve upwards of 10 billion tons sequestered CO2 per year by 2025 (seven billion tons from biological ocean sequestration and at least three billion tons from geologic and terrestrial sequestration). Assuming a contract term of 40 years, and a parallel commodity market continues to develop for CO2 credits, at some time in the future the WTO's contractual price will be less than the commodity market price – and the WTO begins to recover its investment. Under one set of assumptions, the net WTO annual subsidy would peak at $86 billion by 2022, equal to an across-the-board WTO tariff on imports and exports of about 1.01%, then become positive a few years later as the market price climbed above WTO's contracted price. Under this proposal, the WTO effectively subsidizes CO2 sequestration in the near to medium term and then recoups its investment and reaps large profits over the long term. http://www.atmocean.com
U43C-1411 INVITED
Carbon-Neutral Energy Supply and Energy Demand-Reduction Technology Needed for Continued Economic Growth Without Dangerous Interference in the Climate System
Stabilization of atmospheric CO2 at levels likely to avoid unacceptable climate risk will require a major transformation in the ways we produce and use energy. Most of our energy will need to come from sources that do not emit carbon dioxide to the atmosphere and that energy will need to be used efficiently. The required reduction of carbon dioxide emissions as global energy consumption and GDP grow imposes quantitative requirements on some combination of carbon-neutral primary power and energy demand reduction. (Emission reductions are expressed relative to an implicit or explicit baseline; explicit being better for policy-making. Energy demand reduction involves both efficiency improvements and lifestyle changes.) These requirements can be expressed as CO2 emission reductions needed, or as carbon-neutral primary power production needed combined with power not used by virtue of increased energy end use efficiency or lifestyle changes ("negawatts"), always subject to some reasonably well-characterized uncertainty limits. Climatic changes thus far have been closer to the more extreme zone of the climatic uncertainty envelope of global warming indicating the potential for disastrous impacts by mid-century and beyond for business-as-usual. Emission reductions needed to avoid "dangerous interference in the climate system" imply a revolutionary change in the global energy system beginning now; particularly ominous are massive conventional coal-fired electric power energy infrastructures under construction by the US, China & India. Strong arguments, based on physical science considerations, exist for prompt measures such as (1) an immediate moratorium on coal-fired plants that don't sequester CO2, (2) a gradually increasing price on carbon emissions and (3) regulatory standards, for example, that would encourage utilities and car manufacturers to improve efficiency, and (4) Apollo-scale R & D projects beginning now to develop sustainable carbon-neutral power that can be deployed on a planetary scale soon enough to matter.
U43C-1412
Community Perceptions of Geologic Sequestration
Political momentum for mitigating climate change through the use of large-scale energy technologies such as geologic sequestration is growing. This paper explores the views of communities living near an actual or potential geologic sequestration project site. Given the potential importance of geologic sequestration to U.S. energy policy, what might explain and influence the views of this technology by the community-members. Through focus groups and one-on-one interviews, we gathered the views of two communities in California's Central Valley. One community close to a Department of Energy sponsored geologic sequestration pilot-project and another similarly located community that is not actually a project site. Our analysis combined a review of the history of the communities with other technologies and their social and economic indicators with the results of the focus groups and interviews. The results suggest that the sense of community empowerment, as contextualized by the history of the community and socio-economic indicators, is an important indicator of positive views of geologic sequestration. In addition, the results indicate community members prefer to be informed about geologic sequestration from a variety of sources (e.g., academia and industry).
U43C-1413
Development Potential for California's Offshore Wind Energy Resource
An initial analysis was performed for areas suitable for offshore wind farm development near the California coast. The siting of an offshore wind farm is limited by water depth, with shallow water being the most preferable economically. Acceptable depths for offshore wind farms were broken up into three categories, based on current and future wind turbine tower support technology; <e;20 meters depth for monopile towers, <e;50 meters for water jacket tripods/quadrapods, and <e; 200 meters depth for deep water floating tower technology which is likely to be developed in the next 15 years. Using the Penn State/National Center for Atmospheric Research Mesoscale Model version 5 (MM5) to predict winds aloft at high resolution (1.67 and 5 km) near the locations of interest, annual 80 meter wind speeds were found for each area. Annual 80 meter wind speeds were based on the average of January, April, July, and Octobers' 2005/2006 MM5 model data. The interannual variation is also examined. Floating buoys were used to validate the surface level winds off the California coast. Using the REpower 5M 5.0 MW, 126 meter diameter offshore wind turbine, a preliminary overall resource assessment was made for coastal California. Initial estimates show that 2-10 TWh, 9-27 TWh, and 67-293 TWh of energy could be harnessed annually using monopile, state of the art, and future turbine support technology in Northern California, the Bay Area, and Southern California respectively. http://www.stanford.edu/~dvorak/