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1.
A controlled field pilot has been developed in Bozeman, Montana, USA, to study near surface CO 2 transport and detection technologies. A slotted horizontal well divided into six zones was installed in the shallow subsurface. The scale and CO 2 release rates were chosen to be relevant to developing monitoring strategies for geological carbon storage. The field site was characterized before injection, and CO 2 transport and concentrations in saturated soil and the vadose zone were modeled. Controlled releases of CO 2 from the horizontal well were performed in the summers of 2007 and 2008, and collaborators from six national labs, three universities, and the U.S. Geological Survey investigated movement of CO 2 through the soil, water, plants, and air with a wide range of near surface detection techniques. An overview of these results will be presented. 相似文献
2.
Surface water gross primary production potential (pGPP), respiration (RESP), metabolism potential (pMET), and CO 2 fluxes in Hilo Bay, Hawai’i, USA, were examined along two river plumes during storm (high-flow) and non-storm (low-flow)
conditions. Significant differences in pGPP, RESP, and pMET were found between low- and high-flow conditions, with lowest
rates of all processes occurring during high-flow conditions. CO 2 fluxes were influenced by metabolic processes at all but one site, with the bay’s surface waters being autotrophic and a
sink for atmospheric CO 2 during low-flow conditions and less autotrophic and a source of atmospheric CO 2 during high-flow conditions. Significant differences in pMET were found between the two river plumes during low-flow conditions
at spatial scales of 1.5 km; however, no differences between river plumes were found during high-flow conditions. Our study
suggests that an increase in storms associated with global climate change could impact surface water metabolic dynamics of
tropical estuaries. 相似文献
3.
A field facility located in Bozeman, Montana provides the opportunity to test methods to detect, locate, and quantify potential
CO 2 leakage from geologic storage sites. From 9 July to 7 August 2008, 0.3 t CO 2 day −1 were injected from a 100-m long, ~2.5-m deep horizontal well. Repeated measurements of soil CO 2 fluxes on a grid characterized the spatio-temporal evolution of the surface leakage signal and quantified the surface leakage
rate. Infrared CO 2 concentration sensors installed in the soil at 30 cm depth at 0–10 m from the well and at 4 cm above the ground at 0 and
5 m from the well recorded surface breakthrough of CO 2 leakage and migration of CO 2 leakage through the soil. Temporal variations in CO 2 concentrations were correlated with atmospheric and soil temperature, wind speed, atmospheric pressure, rainfall, and CO 2 injection rate. 相似文献
4.
Simulation of carbon dioxide (CO 2) at hourly/weekly intervals and fine vertical resolution at the continental or coastal sites is challenging because of coarse horizontal resolution of global transport models. Here the regional Weather Research and Forecasting (WRF) model coupled with atmospheric chemistry is adopted for simulating atmospheric CO 2 (hereinafter WRF-CO 2) in nonreactive chemical tracer mode. Model results at horizontal resolution of 27 × 27 km and 31 vertical levels are compared with hourly CO 2 measurements from Tsukuba, Japan (36.05°N, 140.13 oE) at tower heights of 25 and 200 m for the entire year 2002. Using the wind rose analysis, we find that the fossil fuel emission signal from the megacity Tokyo dominates the diurnal, synoptic and seasonal variations observed at Tsukuba. Contribution of terrestrial biosphere fluxes is of secondary importance for CO 2 concentration variability. The phase of synoptic scale variability in CO 2 at both heights are remarkably well simulated the observed data (correlation coefficient >0.70) for the entire year. The simulations of monthly mean diurnal cycles are in better agreement with the measurements at lower height compared to that at the upper height. The modelled vertical CO 2 gradients are generally greater than the observed vertical gradient. Sensitivity studies show that the simulation of observed vertical gradient can be improved by increasing the number of vertical levels from 31 in the model WRF to 37 (4 below 200 m) and using the Mellor–Yamada–Janjic planetary boundary scheme. These results have large implications for improving transport model simulation of CO 2 over the continental sites. 相似文献
5.
In March 1994, soil gases were sampled in the area of Vulcano Porto, on the island of Vulcano, using a grid of about 200 points/km 2. Analysed gases were CO 2, He and 222Rn and, over a smaller area, H 2S. Some of the samples were also analysed for the isotope composition of CO 2C. Three anomalous CO 2 degassing areas were identified: Grotta dei Palizzi, the area near the Telephone Exchange, and the area near the beach fumaroles. The behaviour of He and 222Rn is different in these 3 areas. The concentration of He is much lower than that of atmospheric He (down to −3950 ppb) in the isthmus, and only in the area near Grotta dei Palizzi does it have values significantly higher than atmospheric ones (up to 1900 ppb). The activity of 222Rn, always significantly positively related to CO 2 concentrations, peaked in the 2 fumarole areas (isthmus, Telephone Exchange). 相似文献
6.
Release of CO 2 from surface ocean water owing to precipitation of CaCO 3 and the imbalance between biological production of organic matter and its respiration, and their net removal from surface
water to sedimentary storage was studied by means of a quotient θ = (CO 2 flux to the atmosphere)/(CaCO 3 precipitated). θ depends not only on water temperature and atmospheric CO 2 concentration but also on the CaCO 3 and organic carbon masses formed. In CO 2 generation by CaCO 3 precipitation, θ varies from a fraction of 0.44 to 0.79, increasing with decreasing temperature (25 to 5°C), increasing atmospheric
CO 2 concentration (195–375 ppmv), and increasing CaCO 3 precipitated mass (up to 45% of the initial DIC concentration in surface water). Primary production and net storage of organic
carbon counteracts the CO 2 production by carbonate precipitation and it results in lower CO 2 emissions from the surface layer. When atmospheric CO 2 increases due to the ocean-to-atmosphere flux rather than remaining constant, the amount of CO 2 transferred is a non-linear function of the surface layer thickness because of the back-pressure of the rising atmospheric
CO 2. For a surface ocean layer approximated by a 50-m-thick euphotic zone that receives input of inorganic and organic carbon
from land, the calculated CO 2 flux to the atmosphere is a function of the CaCO 3 and C org net storage rates. In general, the carbonate storage rate has been greater than that of organic carbon. The CO 2 flux near the Last Glacial Maximum is 17 to 7×10 12 mol/yr (0.2–0.08 Gt C/yr), reflecting the range of organic carbon storage rates in sediments, and for pre-industrial time
it is 38–42×10 12 mol/yr (0.46–0.50 Gt C/yr). Within the imbalanced global carbon cycle, our estimates indicate that prior to anthropogenic
emissions of CO 2 to the atmosphere the land organic reservoir was gaining carbon and the surface ocean was losing carbon, calcium, and total
alkalinity owing to the CaCO 3 storage and consequent emission of CO 2. These results are in agreement with the conclusions of a number of other investigators. As the CO 2 uptake in mineral weathering is a major flux in the global carbon cycle, the CO 2 weathering pathway that originates in the CO 2 produced by remineralization of soil humus rather than by direct uptake from the atmosphere may reduce the relatively large
imbalances of the atmosphere and land organic reservoir at 10 2–10 4-year time scales. 相似文献
7.
Coastal wetlands are hotspots for biodiversity and biological productivity, yet the hydrology and carbon cycling within these systems remains poorly understood due to their complex nature. By using a novel spatiotemporal approach, this study quantified groundwater discharge and the related inputs of acidity and CO 2 along a continuum of a modified coastal acid sulphate soil (CASS) wetland, a coastal lake and an estuary under highly contrasting hydrological conditions. To increase the resolution of spatiotemporal data and advance upon previous methodologies, we relied on automated observations from four simultaneous time-series stations to develop multiple radon mass balance models to estimate groundwater discharge and related groundwater inputs of acidity and dissolved inorganic carbon (DIC), along with surface water to atmosphere CO 2 fluxes. Spatial surveys indicated distinct acid hotspots with minimum surface water pH of 2.91 (dry conditions) and 2.67 (flood conditions) near a non-remediated (drained) CASS area. Under flood conditions, groundwater discharge accounted for ~14.5 % of surface water entering the lake. During the same period, acid discharge from the acid sulphate soil section of the continuum produced ~4.8 kg H 2SO 4?ha ?1 day ?1, a rate much higher than previous studies in similar systems. During baseflow conditions, the low pH water was rapidly buffered within the estuarine lake, with the pH increasing from 4.22 to 6.07 over a distance of ~250 m. The CO 2 evasion rates within the CASS were extremely high, averaging 2163?±?125 mmol m ?2 day ?1 in the dry period and 4061?±?259 mmol m ?2 day ?1 under flood conditions. Groundwater input of DIC could only account for 0.4 % of this evasion in the dry conditions and ~5 % during the flood conditions. We demonstrated that by utilising a spatiotemporal (multiple time-series stations) approach, the study was able to isolate distinct zones of differing hydrology and biogeochemistry, whilst providing more reasonable groundwater acid input estimates and air–water CO 2 flux estimates than some traditional sampling designs. This study highlights the notion that modified CASS wetlands can release large amounts of CO 2 to the atmosphere because of high groundwater acid inputs and extremely low surface water pH. 相似文献
8.
It was shown that the history of the biosphere is closely related to processes caused by low solar luminosity. Solar radiation is insufficient to maintain the Earth’s surface temperature above the freezing point of water. Positive temperatures are kept owing to the presence of greenhouse gases in the atmosphere: CO 2, CH 4, and others. Certain stages in the development of the biosphere and climate are related to these effects. Methane was the main carbon-bearing gas in the primordial atmosphere. It compensated the low solar luminosity. Life originated under the reduced conditions of the early Earth. Methane-producing biota was formed. Methane remained to be the main greenhouse gas in the Archean. The release of molecular oxygen into the atmosphere 2.4 Ga ago resulted in the disruption of the established mechanism of the compensation of the low solar luminosity. Methane ceased to cause a significant greenhouse effect, and the content of carbon dioxide was insufficient to play this role. A global glaciation began and had lasted for approximately 200 million years. However, the increasing CO 2 content in the atmosphere reached eventually a level sufficient for the compensation for the low solar luminosity. The glaciation period came to an end. Simultaneously, a conflict arose between the role of CO 2 as a gas controlling the thermal regime of the planet and as an initial material for biota production. As long as the resource of biotic carbon was inferior to that of atmospheric CO 2, the uptake of atmospheric CO 2 related to sporadic increases in biologic production was insufficient for a significant change in the thermal regime. This was the reason for a long-term climate stabilization for 1.5 billion years. By 0.8 Ga, the resource of oceanic biota reached the level at which variations in the uptake of atmospheric CO 2 related to variations in the production of organic and carbonate carbon became comparable with the resource of atmospheric CO 2. Since then, an oscillatory equilibrium has been established between the intensity of biota development and climate-controlling CO 2 content in the atmosphere. Glaciation and warming periods have alternated. These changes were triggered by various geologic events: intensification or attenuation of volcanism; growth, breakup, or migration of continents; large-scale magmatism; etc. A new relation between atmospheric CO 2 and biotic carbon was established in response to the emergence of terrestrial biota and the appearance of massive buffers of organic carbon on land. The interrelation of the biosphere and climate changed. 相似文献
9.
One possible way of mitigating carbon dioxide (CO 2) emissions from fossil fuel combustion is using carbon dioxide capture and storage (CCS) technology. However, public perception concerning CO 2 storage in the geosphere is generally negative, being particularly motivated by perceived leakage risks. Therefore, a main issue when attempting to gain public acceptance is ensuring provision of appropriate monitoring practices, aimed at providing health, safety and environmental risk assessment, so that potential risks from CO 2 storage are minimized. Naturally occurring CO 2 deposits provide unique natural analogues for evaluating and validating methods used for the detection and monitoring of CO 2 spreading and degassing into the atmosphere. Geological and hydrological structures of the Cheb Basin (NW Bohemia, Czech Republic) represent such a natural analogue for investigating CO 2 leakage and offer a perfect location at which to verify monitoring tools used for direct investigation of processes along preferential migration paths. This shallow basin dating from the Tertiary age is characterized by up to 300?m thick Neogene sediment deposits and several tectonically active faults. The objectives of this paper are to introduce the CO 2 analogues concept to present the Eger Rift as a suitable location for a natural CO 2 analogue site and to demonstrate to what extent such an analogue site should be used (with a case study). The case study presents the results obtained from a joint application of geoelectrical measurements in combination with soil CO 2 concentration and flux determination methods, for the detection and characterization of natural CO 2 releases at gas seeps (as part of a hierarchic monitoring concept). To highlight discharge-controlling structural near surface features was the initial motivation for the application of geoelectrical measurements. Soil-gas concentration and flux measurement techniques are relatively simple to employ and are valuable methods that can be used to monitor seeping CO 2 along preferential pathways. Joint interpretation of both approaches yields a first insight into fluid paths and reveals that the thickness and permeability of site-specific near surface sedimentary deposits have a great influence upon the spatial distribution of the CO 2 degassing pattern at surface level. 相似文献
10.
In this paper, Shell’s in-house reservoir simulator MoReS is applied to a recently introduced CO 2 sequestration benchmark problem entitled “Estimation of the CO 2 Storage Capacity of a Geological Formation” (Class et al. 2008). The principal objective of this benchmark is the simulation of CO 2 distribution within a modeling region, and leakage of CO 2 outside of it, for a period of 50 years. This study goes beyond the benchmarking exercise to investigate additional factors
with direct relevance to CO 2 storage capacity estimations: water and gas relative permeabilities, permeability anisotropy, presence of sub-seismic features
(conductive fractures, thin shale layers), regional hydrodynamic gradient, CO 2-enriched brine convection (due to brine density differences), and injection rates. The effects of hydrodynamic gradients
and gravitationally induced convection only become significant over 100 s of years. This study has thus extended simulation
time to 1,000 years. It is shown that grid resolution significantly impacts results. Vertical-grid refinement results in larger
and thinner CO 2 plumes. Lateral-grid refinement delays leakage out of the model domain and reduces injection pressure for a given injection
rate. Sub-seismic geological features such as fractures/faults and shale layers are demonstrated to have impact on CO 2 sequestration. Fractures located up-dip from the injector may lead to more leakage while the opposite may happen in the presence
of fractures perpendicular to the dip. Thin shale layers produce stacked CO 2 blankets. They should be explicitly represented instead of being upscaled using a reduced vertical to horizontal permeability
ratio. Results are seen to be far more sensitive to gas relative permeability and hysteresis than to variations in the water
relative permeability models used. For a multi-injectors project, there is scope to optimize the phasing of injections to
avoid potential fracturing near injectors. 相似文献
11.
The mechanisms for storage of CO 2 in rock formations include structural/stratigraphic, mineral, solubility and residual trapping. Residual trapping is very important in terms of both containment security and storage capacity. However, to date, the contribution from residual trapping (i.e. immobilisation of supercritical fluid via capillarity in pore spaces) is still relatively difficult to quantify accurately. Using a laboratory-based testing program, this study demonstrates the feasibility of using reactive ester tracers (i.e. triacetin, propylene glycol diacetate and tripropionin), which partition between a mobile water phase and a stationary supercritical CO 2 phase, to quantify the residual CO 2 saturation, Sgr, of a rock formation. The proposed single-well test involves injecting these tracers into the subsurface, followed by CO 2 saturated water, where the ester tracers slowly hydrolyse to form products with differing partition coefficients. After a suitable period of time, allowing for partial hydrolysis, water containing the tracer mixture is produced from the subsurface and analysed using gas chromatography mass spectrometry (GCMS). A numerical simulator of the tracer behaviour in a reservoir is used to explain the differential breakthrough of these tracer compounds during water production to estimate Sgr. Computer modelling suggests that the use of esters tracers to determine CO 2 residual saturation is a potentially robust method. The supercritical CO 2/water partition coefficients directly dictate the amount of time that each tracer spends in the CO 2 and water phases. As such for modelling of tracer behaviour and estimating Sgr, knowing the tracer partition coefficient is essential; in this paper, the first laboratory study to determine the partition coefficients of these reactive ester tracers is described. 相似文献
12.
Carbon capture and sequestration (CCS) is one of the important options available for partially stemming greenhouse gas emissions from large point sources. The possibility of leaking from deep storage needs to be addressed. The Wadi Namaleh area in southern Jordan provides an interesting case study of how excess CO 2 can be trapped in the form of carbonates in the near surface, even when the local geology is not obviously conducive for such a process.Carbonate veins are formed in surface alteration zones of rhyolite host rock in this arid region. The alteration zones are limited to areas where surface soil or colluvium are present. Oxygen, deuterium and carbon isotopes of the carbonates and near-surface ground water in the area suggest that the source of carbon is deep seated CO 2, and that the carbonate precipitated in local meteoric water under ambient temperature conditions. Analysis of strontium in the carbonate, fresh rhyolite and altered host shows that the source for calcium is aeolian. Trace elements show that metal and REE mobility are constrained to the alteration zone.Thus, interaction of H 2O, CO 2 and atmospheric wet and dry deposition lead to the formation of the clayey (montmorillonite) alteration zone. This zone acts to trap seeping CO 2 and water, and thus produces conditions of progressively more efficient trapping of carbon dioxide by means of a positive feedback mechanism. Replication of these conditions in other areas will minimize CO 2 leakage from man-made CCS sites. 相似文献
13.
Far from equilibrium enstatite dissolution rates both open to atmospheric CO 2 and CO 2 purged were measured as a function of solution pH from 8 to 13 in batch reactors at room temperature. Congruent dissolution was observed after an initial period of incongruent dissolution with preferential Si release from the enstatite. Steady-state dissolution rates in open to atmospheric CO 2 conditions decrease with increase in solution pH from 8 to 12 similar to the behavior reported by other investigators. Judging from the pH 13 dissolution rate, rates increase with pH above pH 12. This is thought to occur because of the increase in overall negative surface charges on enstatite as Mg surface sites become negative above pH 12.4, the pH of zero surface charge of MgO.Steady-state dissolution rates of enstatite increase above pH 10 when CO 2 was purged by performing the experiments in a N 2 atmosphere. This suggests inhibition of dissolution rates above pH 10 when experiments were open to the atmosphere. The dissolved carbonate in these solutions becomes dominantly CO 32− above pH 10.33. It is argued that CO 32− forms a >Mg 2-CO 3 complex at positively charged Mg surface sites on enstatite, resulting in stabilization of the surface Si-O bonds. Therefore, removal of solution carbonate results in an increase in dissolution rates of enstatite above pH 10. The log rate of CO 2-purged enstatite dissolution in moles per cm 2 per s as a function of increasing pH above pH 10 is equal to 0.35. This is consistent with the model of silicate mineral dissolution in the absence of surface carbonation in alkaline solutions proposed earlier in the literature. 相似文献
14.
The continent is the second largest carbon sink on Earth’s surface. With the diversification of vascular land plants in the late Paleozoic, terrestrial organic carbon burial is represented by massive coal formation, while the development of soil profiles would account for both organic and inorganic carbon burial. As compared with soil organic carbon, inorganic carbon burial, collectively known as the soil carbonate, would have a greater impact on the long-term carbon cycle. Soil carbonate would have multiple carbon sources, including dissolution of host calcareous rocks, dissolved inorganic carbon from freshwater, and oxidation of organic matter, but the host calcareous rock dissolution would not cause atmospheric CO2 drawdown. Thus, to evaluate the potential effect of soil carbonate formation on the atmospheric pCO2 level, different carbon sources of soil carbonate should be quantitatively differentiated. In this study, we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop, consisting of limestone of the early Paleogene Guanzhuang Group in North China. Based on the C and Mg isotope data, we developed a numerical model to quantify the carbon source of calcite veins. The modeling results indicate that 4–37 wt% of carbon in these calcite veins was derived from atmospheric CO2. The low contribution from atmospheric CO2 might be attributed to the host limestone that might have diluted the atmospheric CO2 sink. Nevertheless, taking this value into consideration, it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2 within 2000 years, i.e., soil carbonate alone would sequester all atmospheric CO2 within 1 million years. Finally, our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate. 相似文献
15.
Geologic storage of CO 2 is expected to produce plumes of large areal extent, and some leakage may occur along fractures, fault zones, or improperly
plugged pre-existing wellbores. A review of physical and chemical processes accompanying leakage suggests a potential for
self-enhancement. The numerical simulations presented here confirm this expectation, but reveal self-limiting features as
well. It seems unlikely that CO 2 leakage could trigger a high-energy run-away discharge, a so-called “pneumatic eruption,” but present understanding is insufficient
to rule out this possibility. The most promising avenue for increasing understanding of CO 2 leakage behavior is the study of natural analogues. 相似文献
16.
We evaluate whether the global weathering budget is near steady state for the pre-anthropogenic modern environment by assessing the magnitude of acidity-generating volcanic exhalations. The weathering rate induced by volcanic acid fluxes, of which the CO 2 flux is the most important, can be expressed as an average release rate of dissolved silica, based on a model feldspar-weathering scheme, and the ratio of carbonate-to-silicate rock weathering. The theoretically predicted flux of silica from chemical weathering is slightly smaller than the estimated global riverine silica flux. After adjustment for carbonate weathering, the riverine dissolved bicarbonate flux is larger than the volcanic carbon degassing rate by a factor of about three. There are substantial uncertainties associated with the calculated and observed flux values, but the modern system may either not be in steady state, or additional, “unknown” carbon sources may exist. The closure errors in the predicted budgets and observed riverine fluxes suggest that continental weathering rates might have had an impact on atmospheric CO 2 levels at a time scale of 10 3-10 4 years, and that enhanced weathering rates during glacial periods might have been a factor in the reduced glacial atmospheric CO 2 levels. Recent anthropogenic emissions of carbon and sulfur have a much larger acid-generating capacity than the natural fluxes. Estimated potential weathering budgets to neutralize these fluxes are far in excess of observed values. A theoretical scenario for a return to steady state at the current anthropogenic acidity emissions (disregarding the temporary buffering action of the ocean reservoir) requires either significantly lower pH values in continental surface waters as a result of storage of strong acids, and/or higher temperatures as a result of enhanced atmospheric CO 2 levels in order to create weathering rates that can neutralize the total flux of anthropogenic and natural background acidity. 相似文献
17.
Approximately 300 kg/day of food-grade CO 2 was injected through a perforated pipe placed horizontally 2–2.3 m deep during July 9–August 7, 2008 at the MSU-ZERT field test to evaluate atmospheric and near-surface monitoring and detection techniques applicable to the subsurface storage and potential leakage of CO 2. As part of this multidisciplinary research project, 80 samples of water were collected from 10 shallow monitoring wells (1.5 or 3.0 m deep) installed 1–6 m from the injection pipe, at the southwestern end of the slotted section (zone VI), and from two distant monitoring wells. The samples were collected before, during, and following CO 2 injection. The main objective of study was to investigate changes in the concentrations of major, minor, and trace inorganic and organic compounds during and following CO 2 injection. The ultimate goals were (1) to better understand the potential of groundwater quality impacts related to CO 2 leakage from deep storage operations, (2) to develop geochemical tools that could provide early detection of CO 2 intrusion into underground sources of drinking water (USDW), and (3) to test the predictive capabilities of geochemical codes against field data. Field determinations showed rapid and systematic changes in pH (7.0–5.6), alkalinity (400–1,330 mg/l as HCO 3), and electrical conductance (600–1,800 μS/cm) following CO 2 injection in samples collected from the 1.5 m-deep wells. Laboratory results show major increases in the concentrations of Ca (90–240 mg/l), Mg (25–70 mg/l), Fe (5–1,200 ppb), and Mn (5–1,400 ppb) following CO 2 injection. These chemical changes could provide early detection of CO 2 leakage into shallow groundwater from deep storage operations. Dissolution of observed carbonate minerals and desorption-ion exchange resulting from lowered pH values following CO 2 injection are the likely geochemical processes responsible for the observed increases in the concentrations of solutes; concentrations generally decreased temporarily following four significant precipitation events. The DOC values obtained are 5 ± 2 mg/l, and the variations do not correlate with CO 2 injection. CO 2 injection, however, is responsible for detection of BTEX (e.g. benzene, 0–0.8 ppb), mobilization of metals, the lowered pH values, and increases in the concentrations of other solutes in groundwater. The trace metal and BTEX concentrations are all significantly below the maximum contaminant levels (MCLs). Sequential leaching of core samples is being carried out to investigate the source of metals and other solutes. 相似文献
18.
Instances of gas leakage from naturally occurring CO 2 reservoirs and natural gas storage sites serve as analogues for the potential release of CO 2 from geologic storage sites. This paper summarizes and compares the features, events, and processes that can be identified
from these analogues, which include both naturally occurring releases and those associated with industrial processes. The
following conclusions are drawn: (1) carbon dioxide can accumulate beneath, and be released from, primary and secondary shallower
reservoirs with capping units located at a wide range of depths; (2) many natural releases of CO 2 are correlated with a specific event that triggered the release; (3) unsealed fault and fracture zones may act as conduits
for CO 2 flow from depth to the surface; (4) improperly constructed or abandoned wells can rapidly release large quantities of CO 2; (5) the types of CO 2 release at the surface vary widely between and within different leakage sites; (6) the hazard to human health was small in
most cases, possibly because of implementation of post-leakage public education and monitoring programs; (7) while changes
in groundwater chemistry were related to CO 2 leakage, waters often remained potable. Lessons learned for risk assessment associated with geologic carbon sequestration
are discussed.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
19.
Anthropogenic greenhouse gas emissions may be offset by sequestering carbon dioxide (CO 2) through the carbonation of magnesium silicate minerals to form magnesium carbonate minerals. The hydromagnesite [Mg 5(CO 3) 4(OH) 2·4H 2O] playas of Atlin, British Columbia, Canada provide a natural model to examine mineral carbonation on a watershed scale. At near surface conditions, CO 2 is biogeochemically sequestered by microorganisms that are involved in weathering of bedrock and precipitation of carbonate minerals. The purpose of this study was to characterize the weathering regime in a groundwater recharge zone and the depositional environments in the playas in the context of a biogeochemical model for CO 2 sequestration with emphasis on microbial processes that accelerate mineral carbonation.Regions with ultramafic bedrock, such as Atlin, represent the best potential sources of feedstocks for mineral carbonation. Elemental compositions of a soil profile show significant depletion of MgO and enrichment of SiO 2 in comparison to underlying ultramafic parent material. Polished serpentinite cubes were placed in the organic horizon of a coniferous forest soil in a groundwater recharge zone for three years. Upon retrieval, the cube surfaces, as seen using scanning electron microscopy, had been colonized by bacteria that were associated with surface pitting. Degradation of organic matter in the soil produced chelating agents and acids that contributed to the chemical weathering of the serpentinite and would be expected to have a similar effect on the magnesium-rich bedrock at Atlin. Stable carbon isotopes of groundwater from a well, situated near a wetland in the southeastern playa, indicate that 12% of the dissolved inorganic carbon has a modern origin from soil CO 2.The mineralogy and isotope geochemistry of the hydromagnesite playas suggest that there are three distinct depositional environments: (1) the wetland, characterized by biologically-aided precipitation of carbonate minerals from waters concentrated by evaporation, (2) isolated wetland sections that lead to the formation of consolidated aragonite sediments, and (3) the emerged grassland environment where evaporation produces mounds of hydromagnesite. Examination of sediments within the southeastern playa–wetland suggests that cyanobacteria, sulphate reducing bacteria, and diatoms aid in producing favourable geochemical conditions for precipitation of carbonate minerals.The Atlin site, as a biogeochemical model, has implications for creating carbon sinks that utilize passive microbial, geochemical and physical processes that aid in mineral carbonation of magnesium silicates. These processes could be exploited for the purposes of CO 2 sequestration by creating conditions similar to those of the Atlin site in environments, artificial or natural, where the precipitation of magnesium carbonates would be suitable. Given the vast quantities of Mg-rich bedrock that exist throughout the world, this study has significant implications for reducing atmospheric CO 2 concentrations and combating global climate change. 相似文献
20.
Perfluorocarbon compounds (PFCs) have high chemical and thermal stability, low background levels in natural systems, and easy detectability. They are proposed as tracers for monitoring potential CO 2 leakage associated with geological carbon sequestration (GCS). The fate of the PFCs in porous media, and in particular, the transport of these compounds relative to CO 2 gas in geological formations, has not been thoroughly studied. We conducted column tests to study the transport of perfluoro-methylcyclo-pentane (PMCP), perfluoro-methylcyclo-hexane (PMCH), ortho-perfluoro-dimethylcyclo-hexane (ortho-PDCH), and perfluoro-trimethylcyclo-hexane (PTCH) gas tracers in a variety of porous media. The influence of water content and sediment minerals on the retardation of the tracers was tested. The transport of PFC tracers relative to 13CO 2 and the conservative tracer sulfur hexafluoride (SF 6) was also investigated. Results show that at high water content, the PFCs and SF 6 transported together. In dry and low-water-content sediments, however, the PFCs were retarded relative to SF 6 with the degree of retardation increasing with the molecular weight of the PFC. When water was present in the medium, the transport of CO 2 was greatly retarded compared to SF 6 and the PFC tracers. However, in dry laboratory sediments, the migration of CO 2 was slightly faster than all the tracers. The type of minerals in the sediments also had a significant impact on the fate of the tracers. In order to use the PFC tracer data obtained from the ground surface or shallow subsurface in a GCS site to precisely interpret the extent and magnitude of CO 2 leakage, the retardation of the tracers and the interaction of CO 2 with the reservoir overlying formation water should be carefully quantified. 相似文献
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