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1.
Laboratory experiments were conducted to investigate the adsorption kinetic behavior of pure and mixed gases (CO2, CH4, approximately equimolar CO2 + CH4 mixtures, and He) on a coal sample obtained from the Black Warrior Basin at the Littleton Mine (Twin Pine Coal Company), Jefferson County, west-central Alabama. The sample was from the Mary Lee coal zone of the Pottsville Formation (Lower Pennsylvanian). Experiments with three size fractions (45–150 µm, 1–2 mm, and 5–10 mm) of crushed coal were performed at 40 °C and 35 °C over a pressure range of 1.4–6.9 MPa to simulate coalbed methane reservoir conditions in the Black Warrior Basin and provide data relevant for enhanced coalbed methane recovery operations. The following key observations were made: (1) CO2 adsorption on both dry and water-saturated coal is much more rapid than CH4 adsorption; (2) water saturation decreases the rates of CO2 and CH4 adsorption on coal surfaces, but it appears to have minimal effects on the final magnitude of CO2 or CH4 adsorption if the coal is not previously exposed to CO2; (3) retention of adsorbed CO2 on coal surfaces is significant even with extreme pressure cycling; and (4) adsorption is significantly faster for the 45–150 μm size fraction compared to the two coarser fractions.  相似文献   

2.
Interpretation of carbon dioxide diffusion behavior in coals   总被引：3，自引：1，他引：3  
Storage of carbon dioxide in geological formations is for many countries one of the options to reduce greenhouse gas emissions and thus to satisfy the Kyoto agreements. The CO2 storage in unminable coal seams has the advantage that it stores CO2 emissions from industrial processes and can be used to enhance coalbed methane recovery (CO2-ECBM). For this purpose, the storage capacity of coal is an important reservoir parameter. While the amount of CO2 sorption data on various natural coals has increased in recent years, only few measurements have been performed to estimate the rate of CO2 sorption under reservoir conditions. An understanding of gas transport is crucial for processes associated with CO2 injection, storage and enhanced coalbed methane (ECBM) production.A volumetric experimental set-up has been used to determine the rate of sorption of carbon dioxide in coal particles at various pressures and various grain size fractions. The pressure history during each pressure step was measured. The measurements are interpreted in terms of temperature relaxation and transport/sorption processes within the coal particles. The characteristic times of sorption increase with increasing pressure. No clear dependence of the characteristic time with respect to the particle size was found. At low pressures (below 1 MPa) fast gas diffusion is the prevailing mechanism for sorption, whereas at higher pressures, the slow diffusion process controls the gas uptake by the coal.  相似文献   

3.
Coal seam degasification and its success are important for controlling methane, and thus for the health and safety of coal miners. During the course of degasification, properties of coal seams change. Thus, the changes in coal reservoir conditions and in-place gas content as well as methane emission potential into mines should be evaluated by examining time-dependent changes and the presence of major heterogeneities and geological discontinuities in the field. In this work, time-lapsed reservoir and fluid storage properties of the New Castle coal seam, Mary Lee/Blue Creek seam, and Jagger seam of Black Warrior Basin, Alabama, were determined from gas and water production history matching and production forecasting of vertical degasification wellbores. These properties were combined with isotherm and other important data to compute gas-in-place (GIP) and its change with time at borehole locations. Time-lapsed training images (TIs) of GIP and GIP difference corresponding to each coal and date were generated by using these point-wise data and Voronoi decomposition on the TI grid, which included faults as discontinuities for expansion of Voronoi regions. Filter-based multiple-point geostatistical simulations, which were preferred in this study due to anisotropies and discontinuities in the area, were used to predict time-lapsed GIP distributions within the study area. Performed simulations were used for mapping spatial time-lapsed methane quantities as well as their uncertainties within the study area. The systematic approach presented in this paper is the first time in literature that history matching, TIs of GIPs and filter simulations are used for degasification performance evaluation and for assessing GIP for mining safety. Results from this study showed that using production history matching of coalbed methane wells to determine time-lapsed reservoir data could be used to compute spatial GIP and representative GIP TIs generated through Voronoi decomposition. Furthermore, performing filter simulations using point-wise data and TIs could be used to predict methane quantity in coal seams subjected to degasification. During the course of the study, it was shown that the material balance of gas produced by wellbores and the GIP reductions in coal seams predicted using filter simulations compared very well, showing the success of filter simulations for continuous variables in this case study. Quantitative results from filter simulations of GIP within the studied area briefly showed that GIP was reduced from an initial ～73 Bcf (median) to ～46 Bcf (2011), representing a 37 % decrease and varying spatially through degasification. It is forecasted that there will be an additional ～2 Bcf reduction in methane quantity between 2011 and 2015. This study and presented results showed that the applied methodology and utilized techniques can be used to map GIP and its change within coal seams after degasification, which can further be used for ventilation design for methane control in coal mines.  相似文献   

4.
The Huntly coalfield has significant coal deposits that contain biogenically-sourced methane. The coals are subbituminous in rank and Eocene in age and have been previously characterised with relatively low to moderate measured gas (CH4) contents (2–4 m3/ton). The CO2 holding capacity is relatively high (18.0 m3/ton) compared with that of CH4 (2.6 m3/ton) and N2 (0.7 m3/ton) at the same pressure (4 MPa; all as received basis). The geothermal gradient is also quite high at 55 °C/km.A study has been conducted which simulates enhancement of methane recovery (ECBM) from these deposits using a new version of the TOUGH2 (version 2) reservoir simulator (ECBM-TOUGH2) that can handle non-isothermal, multi-phase flows of mixtures of water, CH4, CO2 and N2. The initial phase of the simulation is CH4 production for the first 5 years of the field history. The model indicates that methane production can be significantly improved (from less than 80% recovery to nearly 90%) through injection of CO2. However, although an increase in the rate of CO2 injection increases the amount of CO2 sequestered, the methane recovery (because of earlier breakthrough with increasing injection rate) decreases. Modeling of pure N2 injection produced little enhanced CH4 production. The injection of a hypothetical flue gas mixture (CO2 and N2) also produced little increase in CH4 production. This is related to the low adsorption capacity of the Huntly coal to N2 which results in almost instantaneous breakthrough into the production well.  相似文献   

5.
Characterization of coal reservoirs and determination of in-situ physical coal properties related to transport mechanism are complicated due to having lack of standard procedures in the literature. By considering these difficulties, a new approach has been developed proposing the usage of relationships between coal rank and physical coal properties. In this study, effects of shrinkage and swelling (SS) on total methane recovery at CO2 breakthrough (TMRB), which includes ten-year primary methane recovery and succeeding enhanced coalbed methane (ECBM) recovery up to CO2 breakthrough, and CO2 sequestration have been investigated by using rank-dependent coal properties. In addition to coal rank, different coal reservoir types, molar compositions of injected fluid, and parameters within the extended Palmer & Mansoori (P&M) permeability model were considered. As a result of this study, shrinkage and swelling lead to an increase in TMRB. Moreover, swelling increased CO2 breakthrough time and decreased displacement ratio and CO2 storage for all ranks of coal. Low-rank coals are affected more negatively than high-rank coals by swelling. Furthermore, it was realized that dry coal reservoirs are more influenced by swelling than others and saturated wet coals are more suitable for eliminating the negative effects of CO2 injection. In addition, it was understood that it is possible to reduce swelling effect of CO2 on cleat permeability by mixing it with N2 before injection. However, an economical optimization is required for the selection of proper gas mixture. Finally, it is concluded from sensitivity analysis that elastic modulus is the most important parameter, except the initial cleat porosity, controlling SS in the extended P&M model by highly affecting TMRB.  相似文献   

6.
Enhanced coalbed methane (ECBM) involves the injection of a gas, such as nitrogen or carbon dioxide, into the coal reservoir to displace the methane present. Potentially this strategy can offer greater recovery of the coal seam methane and higher rates of recovery due to pressure maintenance of the reservoir. While reservoir simulation forms an important part of the planning and assessment of ECBM, a key question is the accuracy of existing approaches to characterising and representing the gas migration process. Laboratory core flooding allows the gas displacement process to be investigated on intact coal core samples under conditions analogous to those in the reservoir. In this paper a series of enhanced drainage core floods are presented and history matched using an established coal seam gas reservoir simulator, SIMED II. The core floods were performed at two pore pressures, 2 MPa and 10 MPa, and involve either nitrogen or flue gas (90% nitrogen and 10% CO2) flooding of core samples initially saturated with methane. At the end of the nitrogen floods the core flood was reversed by flooding with methane to investigate the potential for hysteresis in the gas displacement process. Prior to the core flooding an independent characterisation programme was performed on the core sample where the adsorption isotherm, swelling with gas adsorption, cleat compressibility and geomechanical properties were measured. This information was used in the history matching of the core floods; the properties adjusted in the history matching were related to the affect of sorption strain on coal permeability and the transfer of gas between cleat and matrix. Excellent agreement was obtained between simulated and observed gas rates, breakthrough times and total mass balances for the nitrogen/methane floods. It was found that a triple porosity model improved the agreement with observed gas migration over the standard dual porosity Warren-Root model. The Connell, Lu and Pan hydrostatic permeability model was used in the simulations and improved history match results by representing the contrast between pore and bulk sorption strains for the 10 MPa cases but this effect was not apparent for the 2 MPa cases. There were significant differences between the simulations and observations for CO2 flow rates and mass balances for the flue gas core floods. A possible explanation for these results could be that there may be inaccuracy in the representation of mixed gas adsorption using the extended Langmuir adsorption model.  相似文献   

7.
Studying gas transport mechanisms in coal seams is crucial in determining the suitability of coal formations for geosequestration and/or CO2-enhanced coal bed methane recovery (ECBM), estimating CO2 storage capacity and recoverable volume of methane, and predicting the long-term integrity of CO2 storage and possible leakages. Due to the dual porosity nature of coal, CO2 transport is a combination of viscous flow and Fickian diffusion. Moreover, CO2 is adsorbed by the coal which leads to coal swelling which can change the porous structure of coal and consequently affects the gas flow properties of coal, i.e. its permeability. In addition, during CO2 permeation, the coal seam undergoes a change in effective stress due to the pore pressure alteration and this can also change the permeability of the coal seam. In addition, depending on the in situ conditions of the coal seam and the plan of the injection scheme, carbon dioxide can be in a supercritical condition which increases the complexity of the problem. We provide an overview of the recent studies on porous structure of coal, CO2 adsorption onto coal, mechanisms of CO2 transport in coalbeds and their measurement, and hydro-mechanical response of coal to CO2 injection and identify opportunities for future research.  相似文献   

8.
Zonguldak coal basin is the only productive hard coal basin of Turkey. The eastern part of the basin is called as Bartin–Amasra District, which has deeper coal seams. The depth and difficulty of mining these coal seams make this district an important candidate for coalbed methane (CBM) recovery. However, there is not enough reservoir data for modeling purposes. In this study, the lithologic information collected for coal mining industry was used to determine the correlations and the continuity of the coal seams. The lithologic information was examined and the depths of the coal seams and the locations of the exploration boreholes were used to perform a reliable correlation using a new method. As a result of the correlation study, 63 continuous coal layers were found. A statistical reserve estimation of each coal layer for methane was made by using Monte Carlo simulation method. The initial methane in place found in the coal layers both in free and adsorbed states were estimated using probabilistic simulations resulted in possible reserve (P10) of 2.07 billion m3, probable reserve (P50) of 1.35 billion m3 and proven reserves (P90) of 0.86 billion m3.Among the determined continuous coal layers, coal layer #26 was selected for a preliminary investigation of the applicability of enhanced coalbed methane (ECBM) recovery and CO2 storage. The scarcity of coal seam reservoir data required a sensitivity study for the effects of reservoir parameters on operational performance indicators. The effects of adsorption, coal density, permeability, cleat porosity and permeability anisotropy parameters were examined using the Computer Modeling Group's (CMG) GEM module.  相似文献   

9.
There is still no clear understanding of the specific interactions between coal and gas molecules. In this context sorption–desorption studies of methane and carbon dioxide, both in a single gas environment and gas mixtures, are of fundamental interest. This paper presents the results of unique simultaneous measurements of sorption kinetics, volumetric strain and acoustic emission (AE) on three tetragonal coal samples subjected to sorption of carbon dioxide and methane mixtures. The coal was a high volatile bituminous C coal taken from the Budryk mine in the Upper Silesia Basin, Poland. Three different gas mixtures were used in the sorption tests, with dominant CO2, with dominant CH4 and a 50/50 mixture.The experimental set-up was designed specially for this study. It consisted of three individual units working together: (i) a unit for gas sorption experiments using a volumetric method, (ii) an AE apparatus for detecting, recording and analysing AE, and (iii) a strain meter for measuring strains induced in the coal sample by gas sorption/desorption. All measurements were computer aided.The experiments indicated that the coal tested showed preferential sorption of CH4 at 2.6 MPa pressure and exhibited comparable affinities for CH4 and CO2 at higher pressures (4.0 MPa). The results of chromatographic analysis of the gas released on desorption suggested that the desorption of methane from the coal was favoured. The relationship between the volumetric strain and the amount of sorbed gas was found to be non-linear. These results were contrary to common opinions on the coal behaviour. Furthermore, it appeared that the swelling/shrinkage of coal was clearly influenced by the network of fractures. Besides, the AE and strain characteristics suggested common sources of sorption induced AE and strain.The present results may have implications for the sequestration of carbon dioxide in coal seams and enhanced coalbed methane recovery (ECBM).  相似文献   

10.
The importance of mitigation of climate change due to greenhouse gas (GHG) emissions from various developmental and infrastructure projects has generated interest at global level to reduce environmental impacts. Life cycle assessment may be used as a tool to assess GHG emissions and subsequent environmental impacts resulting from electricity generation from thermal power plants. This study uses life cycle approach for assessing GHG emissions and their impacts due to natural gas combined cycle (NGCC) and imported coal thermal power plants using the IPCC 2001 and Eco-Indicator 99(H) methods in India for the first time. The total GHG emission from the NGCC thermal power plant was 584 g CO2 eq/kWh electricity generation, whereas in case of imported coal, it was 1,127 g CO2 eq/kWh electricity generation. This shows that imported coal has nearly ~2 times more impacts when compared to natural gas in terms of global warming potential and human health as disability-adjusted life years from climate change due to GHG emissions such as carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O).  相似文献   

11.
Numerical modelling of the processes of CO2 storage in coal and enhanced coalbed methane (ECBM) production requires information on the kinetics of adsorption and desorption processes. In order to address this issue, the sorption kinetics of CO2 and CH4 were studied on a high volatile bituminous Pennsylvanian (Upper Carboniferous) coal (VRr=0.68%) from the Upper Silesian Basin of Poland in the dry and moisture-equilibrated states. The experiments were conducted on six different grain size fractions, ranging from <0.063 to 3 mm at temperatures of 45 and 32 °C, using a volumetric experimental setup. CO2 sorption was consistently faster than CH4 sorption under all experimental conditions. For moist coals, sorption rates of both gases were reduced by a factor of more than 2 with respect to dry coals and the sorption rate was found to be positively correlated with temperature. Generally, adsorption rates decreased with increasing grain size for all experimental conditions.Based on the experimental results, simple bidisperse modelling approaches are proposed for the sorption kinetics of CO2 and CH4 that may be readily implemented into reservoir simulators. These approaches consider the combination of two first-order reactions and provide, in contrast to the unipore model, a perfect fit of the experimental pressure decay curves. The results of this modeling approach show that the experimental data can be interpreted in terms of a fast and a slow sorption process. Half-life sorption times as well as the percentage of sorption capacity attributed to each of the two individual steps have been calculated.Further, it was shown that an upscaling of the experimental and modelling results for CO2 and CH4 can be achieved by performing experiments on different grain size fractions under the same experimental conditions.In addition to the sorption kinetics, sorption isotherms of the samples with different grain size fractions have been related to the variations in ash and maceral composition of the different grain size fractions.  相似文献   

12.
Anthropogenic activities often result in the emissions of methane (CH4) and carbon dioxide (CO2) which are the principal components of greenhouse gases. The mitigation of these gases to avert further occurrence of global warming has attracted a lot of research interest. In this study, the potential of greenhouse gases abatement via catalytic CO2 (dry) reforming of methane to syngas over samarium oxide-supported cobalt (20 wt% Co/80 wt% Sm2O3) catalyst was investigated. The 20 wt% Co/80 wt% Sm2O3 material was synthesized via wet impregnation method and characterized using different instrument techniques. The methane dry reforming reaction, as well as its kinetics over the catalyst, was studied in a stainless steel fixed-bed continuous flow reactor at feed (CH4:CO2) ratios range of 0.1–1.0, temperature range of 923–1023 K and gas hourly space velocity (GHSV) of 30,000 h?1. The 20 wt% Co/80 wt% Sm2O3 catalyst showed promising catalytic activity evident from the highest CH4 and CO2 conversion of ~71 and ~74% as well as the highest hydrogen (H2) and carbon monoxide (CO) yield of ~62 and ~73%, respectively. Moreover, the methane dry reforming over the 20 wt% Co/80 wt% Sm2O3 catalyst produces H2/CO ratio close to unity hence suitable for use as a chemical intermediate for synthesis of oxygenated fuels. The kinetic data obtained from the methane dry reforming were fitted to power law model. Apparent activation energies of 88.62, 80.12, 108.12 and 100.91 kJ mol?1 were obtained for CH4, CO2, H2 and CO, respectively. The characterization of the spent 20 wt% Co/80 wt% Sm2O3 catalyst after 4 h of time-on-stream has confirmed the presence of amorphous carbon which can easily be gasified.  相似文献   

13.
The Black Warrior Basin of the southeastern United States hosts one of the world’s most prolific and long-lived coalbed methane plays, and the wealth of experience in this basin provides insight into the relationships among basin hydrology, production performance, and environmental issues. Along the southeast margin of the basin, meteoric recharge of reservoir coal beds exposed in an upturned fold limb exerts a strong control on water chemistry, reservoir pressure, and production performance. Fresh-water plumes containing Na–HCO3 waters with low TDS content extend from the structurally upturned basin margin into the interior of the basin. Northwest of the plumes, coal beds contain Na–Cl waters with moderate to high-TDS content. Carbon isotope data from produced gas and mineral cements suggest that the fresh-water plumes have been the site of significant bacterial activity and that the coalbed methane reservoirs contain a mixture of thermogenic and late-stage biogenic gases.  相似文献   

14.
An alternative approach is proposed to develop an improved permeability model for coalbed methane (CBM) and CO2-enhanced CBM (ECBM) recovery, and CO2 geosequestration in coal. This approach integrates the textural and mechanical properties to describe the anisotropy of gas permeability in coal reservoirs. The model accounts for the stress dependent deformation using a stress–strain correlation, which allows determination of directional permeability for coals. The stress–strain correlation was developed by combining mechanical strain with sorption-induced strain for any given direction. The mechanical strain of coal is described by the general thermo-poro-elastic constitutive equations for solid materials under isothermal conditions and the sorption-induced strain is approximated by treating the swelling/shrinkage of coal matrix equivalent to the thermal contraction/expansion of materials. With directional strains, the permeability of coal in any given direction can be modeled based on the theory of rock hydraulics. In this study, the proposed model was tested with both literature data and experiments. The experiments were carried out using a specially designed true tri-axial stress coal permeameter (TTSCP). The results show that the proposed model provides better predictions for the literature data compared with other conventional coal permeability models. The model also gives reasonable agreement between the predicted and measured stress–strains and directional permeabilities under laboratory conditions.  相似文献   

15.
The history of life on Earth is critically dependent on the carbon, sulfur and oxygen cycles of the lithosphere – hydrosphere – atmosphere – biosphere system. An Archean oxygen-poor greenhouse atmosphere developed through: (i) accumulation of CO2 and CH4 from episodic injections of CO2 from volcanic activity, volatilised crust impacted by asteroids and comets, metamorphic devolatilisation processes and release of methane from sediments; and (ii) little CO2 weathering-capture due to both high temperatures of the hydrosphere (low CO2 solubility) and a low ratio of exposed continents to oceans. In the wake of the Sturtian glaciation, enrichment in oxygen and appearance of multicellular eukaryotes heralded the onset of the Phanerozoic where greenhouse conditions were interrupted by periods of strong CO2-sequestration through intensified capture of CO2 by marine plants, onset of land plants and burial of carbonaceous shale and coal (Late Ordovician; Carboniferous – Permian; Late Jurassic; Late Tertiary – Quaternary). The progression from Late Mesozoic and Early Tertiary greenhouse conditions to Late Tertiary – Quaternary ice ages was related to the sequestration of CO2 by rapid weathering of the emerging Alpine and Himalayan mountain chains. A number of peak warming and sea-level-rise events include the Late Oligocene, mid-Miocene, mid-Pliocene and Pleistocene glacial terminations. The Late Tertiary – Quaternary ice ages were dominated by cyclic orbital-forcing-triggered terminations which involved CO2-feedback effects from warming seas and the biosphere and albedo flips due to ice-sheet melting. Since ca AD 1750 human emissions were ～305 Gt of carbon, as compared with ～750 Gt C in the atmosphere. The emissions constitute ～12% of the terrestrial biosphere and ～10% of the known global fossil fuel reserve of ～4000 Gt C, whose combustion would compare to the ～ 4600 Gt C released to the atmosphere during the K – T impact event 65 million years ago, with associated ～65% mass extinction of species. The current growth rate of atmospheric greenhouse gases and global mean temperatures exceed those of Pleistocene glacial terminations by one to two orders of magnitude. The relationship between temperatures and sea-levels for the last few million years project future sea-level rises toward time-averaged values of at least 5 m per 1°C. The instability of ice sheets suggested by the Dansgaard – Oeschinger glacial cycles during 50 – 20 ka, observed ice melt lag effects of glacial terminations, spring ice collapse dynamics and the doubling per-decade of Greenland and west Antarctic ice melt suggest that the Intergovernmental Panel on Climate Change's projected sea-level rises (<59 cm) for the 21st century may be exceeded. The biological and philosophical rationale underlying climate change and mass extinction perpetrated by an intelligent carbon-emitting mammal species may never be known.  相似文献   

16.
Complete sorption isotherm characteristics of methane and CO2 were studied on fourteen sub-bituminous to high-volatile bituminous Indian Gondwana coals. The mean vitrinite reflectance values of the coal samples are within the range of 0.64% to 1.30% with varying maceral composition. All isotherms were conducted at 30 °C on dry, powdered coal samples up to a maximum experimental pressure of ~ 7.8 MPa and 5.8 MPa for methane and CO2, respectively.The nature of the isotherms varied widely within the experimental pressure range with some of the samples remained under-saturated while the others attained saturation. The CO2 to methane adsorption ratios decreased with the increase in experimental pressure and the overall variation was between 4:1 and 1.5:1 for most of the coals. For both methane and CO2, the lower-ranked coal samples generally exhibited higher sorption affinity compared to the higher-ranked coals. However, sorption capacity indicates a U-shaped trend with rank. Significant hysteresis was observed between the ad/desorption isotherms for CO2. However, with methane, hysteresis was either absent or insignificant. It was also observed that the coal maceral compositions had a significant impact on the sorption capacities for both methane and CO2. Coals with higher vitrinite contents showed higher capacities while internite content indicated a negative impact on the sorption capacity.  相似文献   

17.
This paper reports on the performance comparison for different CO2-ECBM schemes in relatively thin unminable seams typical of Northern Appalachian coal basin using a horizontal well configuration. Numerical simulations based upon public-domain coalbed reservoir properties indicated that injection of pure CO2 is likely to result in only limited incremental methane recovery if any over primary recovery, due to the low injection rates that can be achieved. On the other hand, the presence of the nitrogen component in the injected gas stream is capable of improving the efficiency of enhanced methane recovery significantly without compromising the net CO2 injection rates, as a result of improved injectivity over pure CO2 injection. There is, however, a trade off between incremental methane recovery and produced gas purity due to early nitrogen breakthrough.  相似文献   

18.
Groundwater may be highly enriched in dissolved carbon species, but its role as a source of carbon to coastal waters is still poorly constrained. Exports of deep and shallow groundwater-derived dissolved carbon species from a small subtropical estuary (Korogoro Creek, Australia, latitude ?31.0478°, longitude 153.0649°) were quantified using a radium isotope mass balance model (233Ra and 224Ra, natural groundwater tracers) under two hydrological conditions. In addition, air-water exchange of carbon dioxide and methane in the estuary was estimated. The highest carbon inputs to the estuary were from deep fresh groundwater in the wet season. Most of the dissolved carbon delivered by groundwater and exported from the estuary to the coastal ocean was in the form of dissolved inorganic carbon (DIC; 687 mmol m?2 estuary day?1; 20 mmol m?2 catchment day?1, respectively), with a large export of alkalinity (23 mmol m?2 catchment day?1). Average water to air flux of CO2 (869 mmol m?2 day?1) and CH4 (26 mmol m?2 day?1) were 5- and 43-fold higher, respectively, than the average global evasion in estuaries due to the large input of CO2- and CH4-enriched groundwater. The groundwater discharge contribution to carbon exports from the estuary for DIC, dissolved organic carbon (DOC), alkalinity, CO2, and CH4 was 22, 41, 3, 75, and 100 %, respectively. The results show that CO2 and CH4 evasion rates from small subtropical estuaries surrounded by wetlands can be extremely high and that groundwater discharge had a major role in carbon export and evasion from the estuary and therefore should be accounted for in coastal carbon budgets.  相似文献   

19.
To stabilize the atmospheric concentration of greenhouse gases (GHG), a huge reduction of carbon dioxide (CO2) emissions is required. Although some people believe that this necessitates a considerable reduction in the use of fossil fuels or fuel switching, other options are available that allow the use of fossil fuels and reduce atmospheric emissions of CO2. Sequestration of CO2 from fossil fuel combustion in the subsurface could prevent the CO2 from reaching the surface for millions of years. Geological sequestration of CO2 in deep aquifers or in depleted oil and gas reservoirs is a mature technology. Despite the huge quantities of CO2 that can be sequestered in this way, this approach does not provide any economic benefit. This paper discusses a third option, which consists of injecting CO2 in deep coal seams to sequester the carbon and enhance the recovery of coalbed methane (CBM). Waste CO2 from CBM-fueled power plants could be injected into CBM reservoirs to produce more methane (CH4) for the power plant. The 2:1 coal-sorption selectivity for CO2 over CH4 supports the feasibility of operating fossil-fueled power plants without atmospheric CO2 emissions. Other CO2 sequestration technologies, such as ocean disposal and biofixation, are briefly discussed and the suitability of these approaches is evaluated for use in Alberta, Canada.  相似文献   

20.
In this study, CO2 storage capacity in unmineable coalbeds in China at depths of 1,000–2,000 m has been evaluated using the methodology recommended by CSLF. This evaluation is one part of the countrywide CO2 storage capacity evaluations in China, initiated by the Chinese Ministry of Land and Resources. This level of CO2 storage capacity evaluation gives a rough scale of assessment with the least site-specific detail. The results show that there is a storage capacity of 98.81 × 108 t CO2 in coalbeds buried at a depth range of 1,000–2,000 m and 4.26 × 1012 m3 additional coalbed methane can be recovered by CO2 injection. These results appear to show great potential and an attractive economic perspective of CO2 storage in unmineable coalbeds in China. Another part of this study is to classify the potential coalbed basins based on CO2 storage capacity and storage capacity per unit area. The study results reveal the distribution of the most potential basins for large-scale CO2 storage and the best economic basins for early CO2 storage in the future.  相似文献   

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