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1.
The typical shape of a capillary-pressure curve is either convex (e.g., Brooks–Corey model) or S-shaped (e.g., van Genuchten model). It is not universally agreed which model reflects natural rocks better. The difference between the two models lies in the representation of the capillary entry pressure. This difference does not lead to significantly different simulation results for modeling CO2 sequestration in aquifers without considering CO2 dissolution. However, we observe that the van-Genuchten-type capillary-pressure model accelerates CO2 solubility trapping significantly compared with the Brooks–Corey-type model. We also show that the simulation results are very sensitive to the slope of the van-Genuchten-type curve around the entry-pressure region. For the representative examples we study, the differences can be so large as to have complete dissolution of the CO2 plume versus persistence of over 50% of the plume over a 5000-year period.The cause of such sensitivity to the capillary-pressure model is studied. Particularly, we focus on how the entry pressure is represented in each model. We examine the mass-transfer processes under gravity-capillary equilibrium, molecular diffusion, convective mixing, and in the presence of small-scale heterogeneities. Laboratory measurement of capillary-pressure curves and some important implementation issues of capillary-pressure models in numerical simulators are also discussed. Most CO2 sequestration simulations in the literature employ one of the two capillary-pressure models. It is important to recognize that these two representations lead to very different predictions of long-term CO2 sequestration. 相似文献
2.
Recent advancements in experimental techniques allow sub-core-scale heterogeneities to be quantified in a high resolution. Based on the observations of heterogeneity distributions in natural core samples, we perform simulations to study the influence of small-scale heterogeneities on large-scale CO2 migration during geological storage. We observe that even the heterogeneities at millimeter scale (the scale of a Representative Elementary Volume for sandstones) can affect large-scale buoyancy-driven upward CO2 migration. For the representative examples we study, ignoring small-scale heterogeneities can lead to an overestimation of the migration speed by a factor of two.To analyze the cause of such overestimation, we introduce a dimensionless heterogeneity factor to characterize different levels of heterogeneity. The influence on CO2 migration is quantified with respect to a variety of heterogeneity factors, correlation lengths, and fluid viscosity ratios for isotropic and anisotropic media. Our findings suggest that small-scale heterogeneities should not be ignored in core analysis, even for cores that appear relatively homogeneous and do not have distinguishable heterogeneous patterns. In addition, relative-permeability curves measured from core-flood experiments under high-flow-velocity conditions (a common practice to eliminate capillary end-effects) should not be directly used in modeling low-velocity CO2 migration if small-scale heterogeneities are present. 相似文献
3.
Soil CO2 concentration data were collected periodically from July 2001 to June 2005 from sampling site grids in two areas located
on the lower flanks of Mt. Etna volcano (Paternò and Zafferana Etnea–Santa Venerina). Cluster analysis was performed on the
acquired data in order to identify possible groups of sites where soil degassing could be fed by different sources. In both
areas three clusters were recognised, whose average CO2 concentration values throughout the whole study period remained significantly different from one another. The clusters with
the lowest CO2 concentrations showed time-averaged values ranging from 980 to 1,170 ppm vol, whereas those with intermediate CO2 concentrations showed time-averaged values ranging from 1,400 to 2,320 ppm vol, and those with the highest concentrations
showed time-averaged values between 1,960 and 55,430 ppm vol. We attribute the lowest CO2 concentrations largely to a biogenic source of CO2. Conversely, the highest CO2 concentrations are attributed to a magmatic source, whereas the intermediate values are due to a variable mixing of the two
sources described above. The spatial distribution of the CO2 values related to the magmatic source define a clear direction of anomalous degassing in the Zafferana Etnea–Santa Venerina
area, which we attribute to the presence of a hidden fault, whereas in the Paternò area no such oriented anomalies were observed,
probably because of the lower permeability of local soil. Time-series analysis shows that most of the variations observed
in the soil CO2 data from both areas were related to changes in the volcanic activity of Mt. Etna. Seasonal influences were only observed
in the time patterns of the clusters characterised by low CO2 concentrations, and no significant interdependence was found between soil CO2 concentrations and meteorological parameters. The largest observed temporal anomalies are interpreted as release of CO2 from magma batches that migrated from deeper to shallower portions of Etna’s feeder system. The pattern of occurrence of
such episodes of anomalous gas release during the observation period was quite different between the two studied areas. This
pattern highlighted an evident change in the mechanism of magma transport and storage within the volcano’s feeder system after
June 2003, interpreted as magma accumulation into a shallow (<8 km depth) reservoir. 相似文献
4.
We present a new petro-elastical and numerical-simulation methodology to compute synthetic seismograms for reservoirs subject
to CO2 sequestration. The petro-elastical equations model the seismic properties of reservoir rocks saturated with CO2, methane, oil and brine. The gas properties are obtained from the van der Waals equation and we take into account the absorption
of gas by oil and brine, as a function of the in situ pore pressure and temperature. The dry-rock bulk and shear moduli can be obtained either by calibration from real data or
by using rock-physics models based on the Hertz-Mindlin and Hashin-Shtrikman theories. Mesoscopic attenuation due to fluids
effects is quantified by using White's model of patchy saturation, and the wet-rock velocities are calculated with Gassmann
equations by using an effective fluid modulus to describe the velocities predicted by White's model. The simulations are performed
with a poro-viscoelastic modeling code based on Biot's theory, where viscoelasticity is described by generalizing the solid/fluid
coupling modulus to a relaxation function. Using the pseudo-spectral method, which allows general material variability, a
complete and accurate characterization of the reservoir can be obtained. A simulation, that considers the Utsira sand of the
North Sea, illustrates the methodology. 相似文献
5.
The oxygen minimum zones (OMZs) are recognized as intense sources of N2O greenhouse gas (GHG) and could also be potential sources of CO2, the most important GHG for the present climate change. This study evaluates, for one of the most intense and shallow OMZ, the Chilean East South Pacific OMZ, the simultaneous N2O and CO2 fluxes at the air–sea interface. Four cruises (2000–2002) and 1 year of monitoring (21°–30°–36°S) off Chile allowed the determination of the CO2 and N2O concentrations at the sea surface and the analysis of fluxes variations associated with different OMZ configurations. The Chilean OMZ area can be an intense GHG oceanic local source of both N2O and CO2. The mean N2O fluxes are 5–10 times higher than the maximal previous historical source in an OMZ open area as in the Pacific and Indian Oceans. For CO2, the mean fluxes are also positive and correspond to very high oceanic sources. Even if different coupling and decoupling between N2O and CO2 are observed along the Chilean OMZ, 65% of the situations represent high CO2 and/or N2O sources. The high GHG sources are associated with coastal upwelling transport of OMZ waters rich in N2O and probably also in CO2, located at a shallow depth. The integrated OMZ role on GHG should be better considered to improve our understanding of the past and future atmospheric CO2 and N2O evolutions. 相似文献
6.
湖泊、河流等内陆水体是连接陆地生态系统和海洋的“长程碳环路”的重要节点,也是温室气体二氧化碳(CO2)排放源,在调节陆地、海洋间的碳迁移转换中发挥着重要作用。相对于自然水体,城市水体因面积小、水深浅且受监测方法限制,水-气界面碳通量经常被忽略。为探讨我国亚热带城市水体温室气体排放特征,本研究以湖南省长沙市典型城市水体,包括洋湖、西湖、松雅湖、月湖4个湖泊和湘江长沙段为研究对象,分别于2022年4和10月采用光化学反馈-腔增强吸收光谱法(OF-CEAS)和扩散模型法对水-气界面CO2通量进行对比测定。结果表明,长沙城市湖泊与河流春季为CO2排放源,秋季为吸收汇,河流水-气界面CO2通量呈显著季节差异。河湖之间CO2通量在春季表现为显著差异,秋季差异不显著。CO2通量与水体溶解氧、水体总氮浓度等呈显著正相关。2种方法的CO2通量对比测定在湖泊上显著相关,但对河流而言相关性不显著。研究揭示的城市湖泊与河流CO2气体的排放特征有利于深入探究城市水体碳的迁移转化,可对全面了解全球气候变化过程和河湖湿地温室气体减排和调控提供科学支撑。 相似文献
7.
The selection and the subsequent design of a subsurface CO2 storage system are subject to considerable uncertainty. It is therefore important to assess the potential risks for health, safety and environment. This study contributes to the development of methods for quantitative risk assessment of CO2 leakage from subsurface reservoirs. The amounts of leaking CO2 are estimated by evaluating the extent of CO2 plumes after numerically simulating a large number of reservoir realizations with a radially symmetric, homogeneous model. To conduct the computationally very expensive simulations, the ‘CO2 Community Grid’ was used, which allows the execution of many parallel simulations simultaneously. The individual realizations are set up by randomly choosing reservoir properties from statistical distributions. The statistical characteristics of these distributions have been calculated from a large reservoir database, holding data from over 1200 reservoirs. An analytical risk equation is given, allowing the calculation of average risk due to multiple leaky wells with varying distance in the surrounding of the injection well. The reservoir parameters most affecting risk are identified. Using these results, the placement of an injection well can be optimized with respect to risk and uncertainty of leakage. The risk and uncertainty assessment can be used to determine whether a site, compared to others, should be considered for further investigations or rejected for CO2 storage. 相似文献
8.
《Physics of the Earth and Planetary Interiors》2002,129(1-2):131-143
The phase diagram for calcite (CaCO3) is re-evaluated in relation to dynamic compression and following release from shock. Available shock compression data on Hugoniot dynamic measurements, analysis of recovered samples, and observation at terrestrial impact sites are compared with theoretically derived equations of state (EOS) for CaCO3 and its decomposition products CaO and CO2. The study results in a refined phase diagram for CaCO3 in which the major change is the extension of the liquid field of CaCO3. A general outcome of this analysis is that release of CO2 from naturally shocked carbonates to the atmosphere is (grossly) overestimated if based on the calcite phase diagram constructed from thermodynamic equilibrium conditions. 相似文献
9.
We report the first measurements of CO2 solubility in molten basalt at pressures comparable to those at which submarine basalts erupt. A basalt from the Juan de Fuca ridge was equilibrated with CO2-rich vapor at 1200°C, 100–1500 bar for up to four hours. After quenching, the glass was analyzed for dissolved carbonate ions by infrared spectroscopy. No forms of dissolved CO2 other than carbonate were detected. CO2 solubility is roughly a linear function of pressure at these low pressures. The experimentally determined solubility differs from previous estimates based on CO2 concentrations of submarine glasses, on CO2 solubilities in basaltic liquids at significantly higher pressures, and on CO2 concentrations of glasses equilibrated with H2OCO2 vapor. Our results are compatible with those obtained previously at higher pressures on a molten Kilauea tholeiite only if there is a significant positive dependence of carbonate solubility on temperature.CO2 contents of mid-ocean ridge glasses measured by infrared spectroscopy are generally higher than would be expected based on solubilities at the hydrostatic pressures for the water depths from which the glasses were recovered, but the lowest dissolved CO2 contents agree with the experimentally determined solubilities. We propose that submarine glasses with low CO2 contents were quenched from magmas that were able to degas because they rose slowly from depth. The common occurrence of glasses with dissolved CO2 contents in excess of the experimentally determined solubility suggests they were quenched from magmas that ascended too rapidly to degas fully. In conjunction with our solubility data, the highest CO2 contents allow minimum estimates of depths to magma chambers. Depths of 2.3 km beneath the ridge are indicated for the East Pacific Rise at 21°N, in agreement with geophysical constraints. 相似文献
10.
The vertical stratification of carbon dioxide (CO2) injected into a deep layered aquifer made up of high-permeability and low-permeability layers, such as Utsira aquifer at Sleipner site in Norway, is investigated with a Buckley–Leverett equation including gravity effects. In a first step, we study both by theory and simulation the application of this equation to the vertical migration of a light phase (CO2), in a denser phase (water), in 1D vertical columns filled with different types of porous media: homogeneous, piecewise homogeneous, layered periodic and finally heterogeneous. For each case, we solve the associated Riemann problems and propose semi-analytical solutions describing the spatial and temporal evolution of the light phase saturation. These solutions agree well with simulation results. We show that the flux continuity condition at interfaces between high-permeability and low-permeability layers leads to CO2 saturation discontinuities at these interfaces and, in particular, to a saturation increase beneath low-permeability layers. In a second step, we analyze the vertical migration of a CO2 plume injected into a 2D layered aquifer. We show that the CO2 vertical stratification under each low-permeability layer is induced, as in 1D columns, by the flux continuity condition at interfaces. As the injection takes place at the bottom of the aquifer the velocity and the flux function decrease with elevation and this phenomenon is proposed to explain the stratification under each mudstone layer as observed at Sleipner site. 相似文献
11.
Expeditions during the summers of 2002 and 2003 implemented continuous monitoring of near-surface (2 m height) atmospheric
CO2 and H2O concentrations at the 4500 m elevation on Muztagata. The resultant data sets reveal a slight decrease of CO2 concentrations (of about 5 μmol·mol-1) and changes in the diurnal variations from the end of June to the middle August. The daily maximum CO2 concentrations occur between 02:30-05:30 AM (local time) and the minimum levels occur between 12:00-15:30 PM. The atmospheric
CO2 concentrations in the summer of 2002 were around 5 μmol·mol-1 lower than those during the same period of 2003, whereas the diurnal amplitude was higher. In contrast, we found that the
daily mean atmospheric H2O content in 2003 was much lower than that in 2002 and there exists a striking negative correlation between CO2 and H2O concentrations. We therefore suggest that the near-surface atmospheric CO2 concentration is affected not only by photosynthesis and respiration, but also by the air H2O content in the glaciated region around Muztagata. 相似文献
12.
A numerical simulation was conducted to predict the change of pCO2 in the ocean caused by CO2 leaked from an underground aquifer, in which CO2 is purposefully stored. The target space of the present model was the ocean above the seafloor. The behavior of CO2 bubbles, their dissolution, and the advection-diffusion of dissolved CO2 were numerically simulated. Here, two cases for the leakage rate were studied: an extreme case, 94,600 t/y, which assumed that a large fault accidentally connects the CO2 reservoir and the seafloor; and a reasonable case, 3800 t/y, based on the seepage rate of an existing EOR site. In the extreme case, the calculated increase in ΔpCO2 experienced by floating organisms was less than 300 ppm, while that for immobile organisms directly over the fault surface periodically exceeded 1000 ppm, if momentarily. In the reasonable case, the calculated ΔpCO2 and pH were within the range of natural fluctuation. 相似文献
13.
Taking Huanglong Ravine and Kangding, Sichuan, and Xiage, Zhongdian, Yunnan, as examples, the authors summarize the hydrogeochemical
and carbon stable isotopic features of the geothermal CO2-water-carbonate rock system and analyze the CO2 sources of the system. It was found that the hydrogeochemical and carbon stable isotopic features of such a system are different
from those of shallow CO2-water-carbonate rock system, which is strongly influenced by biosphere. The former has higher CO2 partial pressure, and is rich in heavy carbon stable isotope. In addition, such a geothermal system is also different from
that developed in igneous rock. The water in the latter system lacks Ca2+, and thus, there are few tufa deposits on ground surface, but it is rich in light carbon stable isotope. Further analysis
shows that CO2 of the geothermal CO2-water-carbonate rock system is a mixture of metamorphic CO2 and magmatic CO2. 相似文献
14.
Edoardo Daly A. Christopher Oishi Amilcare Porporato Gabriel G. Katul 《Advances in water resources》2008
Near-surface soil CO2 gas-phase concentration (C) and concomitant incident rainfall (Pi) and through-fall (Pt) depths were collected at different locations in a temperate pine forest every 30 min during the 2005 and 2006 growing seasons (and then averaged to the daily timescale). At the daily scale, C temporal variations were well described by a sequence of monotonically decreasing functions interrupted by large positive jumps induced by rainfall events. A stochastic model was developed to link rainfall statistics responsible for these jumps to near-surface C dynamics. The model accounted for the effect of daily rainfall variability, both in terms of timing and amount of water, and permitted an analytical derivation of the C probability density function (pdf) using the parameters of the rainfall pdf. Given the observed positive correlation between daily C and soil CO2 fluxes to the atmosphere (Fs), the effects of various rainfall regimes on the statistics of Fs can be deduced from the behavior of C under different climatic conditions. The predictions from this analytical model are consistent with flux measurements reported in manipulative experiments that varied rainfall amount and frequency. 相似文献
15.
Ingrid Cnossen Matthew J. Harris Neil F. Arnold Erdal Yiit 《Journal of Atmospheric and Solar》2009,71(13):1484-1496
We have studied the temperature response to changes in the CO2 concentration in the middle and upper atmosphere using the Coupled Middle Atmosphere–Thermosphere Model 2 (CMAT2). We have performed simulations with a range of CO2 concentrations and three different ways of accounting for the effects of gravity waves, to allow for comparison with previous studies and sensitivity analyses. We initially find that the response of the model to the changes in CO2 concentration which took place between 1965 and 1995 (320–360 ppm) is strongly dependent on the gravity wave parameterization that is used, but this is to a large degree due to steps or kinks in an otherwise nearly linear curve describing the temperature as a function of CO2 concentration. We have not been able to identify the cause of these steps as part of the present study, which is a limitation and must be studied in future work. Here we treated the steps as model noise and rather focused on correcting for their effects by fitting straight lines to the temperature–CO2 curves to estimate the overall slope of the curves. From these slopes we were able to obtain more robust trend estimates than can be obtained by comparing only two model simulations, as is normally done in other, similar studies. The corrected temperature responses to a 40 ppm change in CO2 concentration still show up to 15–17% sensitivity to the gravity wave parameterization in the mesosphere and thermosphere. This remaining sensitivity is likely to be related to the fundamental differences in the way a change in temperature modifies the propagation and dissipation characteristics of gravity waves in each parameterization, which is particularly different for linear and non-linear schemes. The corrected trends we find are largely in agreement with other modelling studies, and therefore do not fully explain observed trends, which are typically larger than those predicted by modelling studies. However, modelling results could be similarly sensitive to other model parameters and settings, for example to gravity wave characteristics or solar activity level, and this should be further investigated as well. 相似文献
16.
M. L. Carapezza B. Badalamenti L. Cavarra A. Scalzo 《Journal of Volcanology and Geothermal Research》2003,123(1-2):81
The northwestern flank of the Colli Albani, a Quaternary volcanic complex near Rome, is characterised by high pCO2 values and Rn activities in the groundwater and by the presence of zones with strong emission of gas from the soil. The most significant of these zones is Cava dei Selci where many houses are located very near to the gas emission site. The emitted gas consists mainly of CO2 (up to 98 vol%) with an appreciable content of H2S (0.8–2%). The He and C isotopic composition indicates, as for all fluids associated with the Quaternary Roman and Tuscany volcanic provinces, the presence of an upper mantle component contaminated by crustal fluids associated with subducted sediments and carbonates. An advective CO2 flux of 37 tons/day has been estimated from the gas bubbles rising to the surface in a small drainage ditch and through a stagnant water pool, present in the rainy season in a topographically low central part of the area. A CO2 soil flux survey with an accumulation chamber, carried out in February–March 2000 over a 12 000 m2 surface with 242 measurement points, gave a total (mostly conductive) flux of 61 tons/day. CO2 soil flux values vary by four orders of magnitude over a 160-m distance and by one order of magnitude over several metres. A fixed network of 114 points over 6350 m2 has been installed in order to investigate temporal flux variations. Six surveys carried out from May 2000 to June 2001 have shown large variations of the total CO2 soil flux (8–25 tons/day). The strong emission of CO2 and H2S, which are gases denser than air, produces dangerous accumulations in low areas which have caused a series of lethal accidents to animals and one to a man. The gas hazard near the houses has been assessed by continuously monitoring the CO2 and H2S concentration in the air at 75 cm from the ground by means of two automatic stations. Certain environmental parameters (wind direction and speed; atm P, T, humidity and rainfall) were also continuously recorded. At both stations, H2S and CO2 exceeded by several times the recommended concentration thresholds. The highest CO2 and H2S values were recorded always with wind speeds less than 1.5 m/s, mostly in the night hours. Our results indicate that there is a severe gas hazard for people living near the gas emission site of Cava dei Selci, and appropriate precautionary and prevention measures have been recommended both to residents and local authorities. 相似文献
17.
内陆水体是大气CO2收支估算的重要组成部分。农业流域分布着大量池塘景观水体,且具备蓄洪抗旱、消纳污染、水产养殖等多种功能。但是,农业流域不同功能的小型池塘CO2排放特征尚不清楚。本研究以极具农业流域代表性的烔炀河流域为研究对象,选取流域中用于水产养殖(养殖塘)、生活污水承纳(村塘)、农业灌溉(农塘)、蓄水(水塘)的4个功能不同的景观池塘,基于为期1年的野外实地观测,以明确农业流域小型池塘CO2排放特征。结果表明,不同功能池塘水体CO2排放差异显著,受养殖活动、生活污水输入和农田灌溉等人类活动影响,养殖塘((80.37±100.39) mmol/(m2·d))、村塘((48.69±65.89) mmol/(m2·d))和农塘((13.50±15.81) mmol/(m2·d))是大气CO2的热点排放源,其CO2排放通量分别是自然蓄水塘((4.52±23.26) mmol/(m2·d))的18、11和3倍。统计分析也表明,该流域池塘CO2排放变化总体上受溶解氧、营养盐等因素驱动。4个不同景观池塘CO2排放通量全年均值为(37.31±67.47) mmol/(m2·d),是不容忽视的CO2排放源,其中养殖塘和村塘具有较高的CO2排放潜力,在未来研究中需要重点关注。 相似文献
18.
藏北高原恶劣的自然地理条件使扎仓茶－卡珍贵的锂资源的开发极为困难,必须采用尽可能简化的提取工艺才能降低成本,本文提出了一种经ＣａＯ,（ＮＨ４）２Ｃ２Ｏ４和Ｎａ２ＣＯ３三步沉积得到粗Ｌｉ２ＣＯ３的简化工艺,其产品纯度可达８５．６２％,总回收率约２０％,卤旦回收率约为７６％。 相似文献
19.
Comparative study on CO2 sources in soil developed on carbonate rock and non-carbonate rock in Central Guizhou 总被引：1，自引：0，他引：1
In this paper, by using concentration and carbon stable isotope the CO2 sources of soil profiles developed on limestone, dolostone and claystone basements in Central Guizhou, China are comparatively
studied. The results show that CO2 concentration of soil profiles developed on different basements is different, having the following sequence: limestone ;
dolostone;claystone. Below the soil depth of 20 cm from the surface the δ13 value of CO2 in soil profile developed on limestone ranges from -12.811%. - -13.492%.(PDB), that in soil profile developed on dolostone
varys from -13.212%. - -14.271%.(PDB) and that in soil profile developed on claystone is about-20.234%. - -21.485%.(PDB).
Taking the carbon isotope of soil organic matter and carbonate rock as two isotopic endmembers, the proportion of soil CO2 generated by dissolution of carbonate rock is calculated, about 21%–25% for soil profile developed on limestone basement,
19%–21% for soil profile developed on dolostone basement. There is almost no influx of CO2 generated by the dissolution of carbonate rock in soil profile developed on claystone basement. 相似文献
20.
Kristian McConville Claudia Halsband Elaine S. Fileman Paul J. Somerfield Helen S. Findlay John I. Spicer 《Marine pollution bulletin》2013
Some planktonic groups suffer negative effects from ocean acidification (OA), although copepods might be less sensitive. We investigated the effect of predicted CO2 levels (range 480–750 ppm), on egg production and hatching success of two copepod species, Centropages typicus and Temora longicornis. In these short-term incubations there was no significant effect of high CO2 on these parameters. Additionally a very high CO2 treatment, (CO2 = 9830 ppm), representative of carbon capture and storage scenarios, resulted in a reduction of egg production rate and hatching success of C. typicus, but not T. longicornis. In conclusion, reproduction of C. typicus was more sensitive to acute elevated seawater CO2 than that of T. longicornis, but neither species was affected by exposure to CO2 levels predicted for the year 2100. The duration and seasonal timing of exposures to high pCO2, however, might have a significant effect on the reproduction success of calanoid copepods. 相似文献