Natural 222Rn as a tracer of mixing and volatilization in a shallow aquifer during a CO2 injection experiment

This study aims to evaluate the application of ²²²Rn in groundwater as a tracer for monitoring CO₂ plume migration in a shallow groundwater system, which is important to detect potential CO₂ leakage in the carbon capture and storage (CCS) project. For this research, an artificial CO₂-infused water injection experiment was performed in a shallow aquifer by monitoring hydrogeochemical parameters, including ²²²Rn. Radon in groundwater can be a useful tracer because of its sensitivity to sudden changes in subsurface environment. To monitor the CO₂ plume migration, the data were analysed based on (a) the influence of mixing processes on the distribution of ²²²Rn induced by the artificial injection experiment and (b) the influence of a carrier gas role by CO₂ on the variation of ²²²Rn. The spatio-temporal distributions of radon concentrations were successfully explained in association with horizontal and vertical mixing processes by the CO₂-infused water injection. Additionally, the mixing ratios of each monitoring well were calculated, quantitatively confirming the influence of these mixing processes on the distribution of radon concentrations. Moreover, one monitoring well showed a high positive relationship between ²²²Rn and Total dissolved inorganic carbon (TIC) by the carrier gas effect of CO₂ through volatilization from the CO₂ plume. It indicated the applicability of ²²²Rn as a sensitive tracer to directly monitor CO₂ leakage. When with a little effect of carrier gas, natural ²²²Rn in groundwater can be used to compute mixing ratio of CO₂-infused water indicative of CO₂ migration pathways. CO₂ carrier gas effect can possibly increase ²²²Rn concentration in groundwater and, if fully verified with more field tests, will pose a great potential to be used as a natural tracer for CO₂.     

Modeling Gaseous CO2 Flow Behavior in Layered Basalts: Dimensional Analysis and Aquifer Response

Particular attention is paid to the risk of carbon dioxide (CO₂) leakage in geologic carbon sequestration (GCS) operations, as it might lead to the failure of sequestration efforts and to the contamination of underground sources of drinking water. As carbon dioxide would eventually reach shallower formations under its gaseous state, understanding its multiphase flow behavior is essential. To this aim, a hypothetical gaseous leak of carbon dioxide resulting from a well integrity failure of the GCS system in operation at Hellisheiði (CarbFix2) is here modeled. Simulations show that migration of gaseous carbon dioxide is largely affected by formation stratigraphy, intrinsic permeability, and retention properties, whereas the initial groundwater hydraulic gradient (0.0284) has practically no effect. In two different scenarios, about 18.3 and 30.6% of the CO₂ that would have been injected by the GCS system for 3 days could be potentially released again into the atmosphere due to a sustained leakage of the same duration. As the gaseous leak occurs, the aquifer experiences high pressure buildups, and the presence of a less conductive layer further magnifies these. Strikingly, the dimensional analysis showed that buoyant and viscous forces can be comparable over time within the predicted gaseous plumes, even far from the leakage source. Local pressure gradients, buoyant, viscous, and capillary forces all play an important role during leakage. Therefore, neglecting one or more of these contributions might lead to a partial prediction of gaseous CO₂ flow behavior in the subsurface, giving space to incorrect interpretations and wrong operational choices.     

Hydrogeochemical characteristics of surface water and groundwater in the karst basin,southwest China

Groundwater is a very significant water source used for irrigation and drinking purposes in the karst region, and therefore understanding the hydrogeochemistry of karst water is extremely important. Surface water and groundwater were collected, and major chemical compositions and environmental isotopes in the water were measured in order to reveal the geochemical processes affecting water quality in the Gaoping karst basin, southwest China. Dominated by Ca²⁺, Mg²⁺, HCO₃^? and SO₄^2?, the groundwater is typically characterized by Ca? Mg? HCO₃ type in a shallow aquifer, and Ca? Mg? SO₄ type in a deeper aquifer. Dissolution of dolomite aquifer with gypsiferous rocks and dedolomitization in karst aquifers are important processes for chemical compositions of water in the study basin, and produce water with increased Mg²⁺, Ca²⁺ and SO₄^2? concentrations, and also increased TDS in surface water and groundwater. Mg²⁺/Ca²⁺ molar ratios in groundwater decrease slightly due to dedolomitization, while the mixing of discharge of groundwater with high Mg²⁺/Ca²⁺ ratios may be responsible for Mg²⁺/Ca²⁺ ratios obviously increasing in surface water, and Mg²⁺/Ca²⁺ ratios in both surface water and groundwater finally tending to a constant. In combination with environmental isotopic analyses, the major mechanism responsible for the water chemistry and its geochemical evolution in the study basin can be revealed as being mainly from the water–rock interaction in karst aquifers, the agricultural irrigation and its infiltration, the mixing of surface water and groundwater and the water movement along faults and joints in the karst basin. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamics and design of systems for geological storage of dissolved CO2

The standard approach for geologic storage of CO₂ consists of injecting it as a supercritical CO₂ phase. This approach places stringent requirements on the caprock, which must display: (1) high entry pressure to prevent the buoyancy driven upwards escape of CO₂; (2) low permeability to minimize the upwards flux of brine displaced by the CO₂; and (3) high strength to ensure that pressure build up does not cause caprock failure. We propose an alternative approach for cases when the above requirements are not met. The approach consists of extracting brine from the storage formation and then re-injecting it so that it mixes with CO₂ at depth in the injection well. Mixing at depth reduces the pressure required for brine and CO₂ at the surface. This CO₂-saturated brine will sink to the aquifer bottom because it is denser than resident brine, which eliminates the risk of buoyant escape of CO₂. The method is particularly favorable when the aquifer dips, because CO₂-saturated brine will tend to flow downslope. We perform two- and three-dimensional numerical simulations to study how far upslope the extraction well needs to be located to ensure a very long operation without CO₂ ever breaking through. Several sets of simulations were carried out to evaluate the effect of slope, temperature, pressure and CO₂ concentration, which is significantly reduced if flue gas (i.e., without capture) is mixed with the brine. We analyze energy requirements to find that the system requires high permeability to be viable, but its performance is improved by taking advantage of the thermal energy of the extracted brine.     

Experimental investigation of injectivity alteration due to salt precipitation during CO2 sequestration in saline aquifers

Injection of CO₂ into saline aquifers causes the geochemical reaction of rock-fluid and salt precipitation due to the evaporation of water as a physical process. Well injectivity is an important issue in carbon capture and storage (CCS) projects because large volumes of CO₂ must be stored for a long time and salt precipitation can significantly reduce injectivity by reducing the permeability. The impact of salt precipitation on the injectivity must therefore be specified in order to maintain the security of CCS projects and enable them to perform at a high level of practicality. The objective of this work is to investigate the influence of the injection rate and brine salinity on injectivity reduction due to evaporation and salt precipitation. In this study, we injected supercritical CO₂ into a sandstone rock sample fully saturated with NaCl brine to characterize the salt precipitation induced by the evaporation process.Evaporation is investigated by mass measurement of the water and vapor produced. The extension in time of salt precipitation and the precipitation profile are analyzed by drying rate measurement, Capillary number and Peclet number. The consequences of salt precipitation on injectivity are specified by permeability and relative permeability analysis. The results show that a high drying rate in the early stage of injection induces rapid salt precipitation. The level of salt precipitation increases with salinity, within a permeability reduction range of 21–66%, and decreases with the injection rate, within a permeability reduction range of 43–62%. The relative permeability of CO₂ is affected by both the injection rate and salinity.     

CO2 Capture and Geologic Storage: The Possibilities

Carbon dioxide (CO₂) capture and geologic storage has been postulated as one possible method to stabilize the atmospheric concentration of CO₂ by injecting and storing it in deep geologic formations. This issue paper analyzes the viability of capture and geologic storage of becoming an effective method to aid in stabilizing the atmospheric concentration of CO₂. It is herein shown that such viability is contingent on overcoming major obstacles that are hydrogeological, technical, and economic in nature. Our analysis indicates that capture and geologic storage is likely to have negligible success in reducing the atmospheric buildup of CO₂ in the coming decades. The magnitude of the anthropogenic emissions of CO₂ indicates that a transition of the world economy away from reliance on fossil fuels might be the only path to stabilize its atmospheric concentration.     

Convective stability analysis of the long-term storage of carbon dioxide in deep saline aquifers

Deep saline aquifers are one of the most suitable geologic formations for carbon sequestration. The linear and global stability analysis of the time-dependent density-driven convection in deep saline aquifers is presented for long-term storage of carbon dioxide (CO₂). The convective mixing that can greatly accelerate the CO₂ dissolution into saline aquifers arises because the density of brine increases upon the dissolution of CO₂ and such a density difference may induce instability. The effects of anisotropic permeability on the stability criteria, such as the critical time for the appearance of convective phenomena and the critical wavelength of the most unstable perturbation, are investigated with linear and global stability analysis. The linear stability analysis provides a sufficient condition for instability while the global stability analysis yields a sufficient condition for stability. The results obtained from these two approaches are not exactly the same but show a consistent trend, both indicating that the anisotropic system becomes more unstable when either the vertical or horizontal permeability increases.     

Prerequisites for density-driven instabilities and convective mixing under broad geological CO2 storage conditions

Direct atmospheric greenhouse gas emissions can be greatly reduced by CO₂ sequestration in deep saline aquifers. One of the most secure and important mechanisms of CO₂ trapping over large time scales is solubility trapping. In addition, the CO₂ dissolution rate is greatly enhanced if density-driven convective mixing occurs. We present a systematic analysis of the prerequisites for density-driven instability and convective mixing over the broad temperature, pressure, salinity and permeability conditions that are found in geological CO₂ storage. The onset of instability (Rayleigh–Darcy number, Ra), the onset time of instability and the steady convective flux are comprehensively calculated using a newly developed analysis tool that accounts for the thermodynamic and salinity dependence on solutally and thermally induced density change, viscosity, molecular and thermal diffusivity. Additionally, the relative influences of field characteristics are analysed through local and global sensitivity analyses. The results help to elucidate the trends of the Ra, onset time of instability and steady convective flux under field conditions. The impacts of storage depth and basin type (geothermal gradient) are also explored and the conditions that favour or hinder enhanced solubility trapping are identified. Contrary to previous studies, we conclude that the geothermal gradient has a non-negligible effect on density-driven instability and convective mixing when considering both direct and indirect thermal effects because cold basin conditions, for instance, render higher Ra compared to warm basin conditions. We also show that the largest Ra is obtained for conditions that correspond to relatively shallow depths, measuring approximately 800 m, indicating that CO₂ storage at such depths favours the onset of density-driven instability and reduces onset times. However, shallow depths do not necessarily provide conditions that generate the largest steady convective fluxes; the salinity determines the storage depth at which the largest steady convective fluxes occur. Furthermore, we present a straight-forward and efficient procedure to estimate site-specific solutal Ra that accounts for thermodynamic and salinity dependence.     

Assessing Methane in Shallow Groundwater in Unconventional Oil and Gas Play Areas,Eastern Kentucky

The expanding use of horizontal drilling and hydraulic fracturing technology to produce oil and gas from tight rock formations has increased public concern about potential impacts on the environment, especially on shallow drinking water aquifers. In eastern Kentucky, horizontal drilling and hydraulic fracturing have been used to develop the Berea Sandstone and the Rogersville Shale. To assess baseline groundwater chemistry and evaluate methane detected in groundwater overlying the Berea and Rogersville plays, we sampled 51 water wells and analyzed the samples for concentrations of major cations and anions, metals, dissolved methane, and other light hydrocarbon gases. In addition, the stable carbon and hydrogen isotopic composition of methane (δ¹³C‐CH₄ and δ²H‐CH₄) was analyzed for samples with methane concentration exceeding 1 mg/L. Our study indicates that methane is a relatively common constituent in shallow groundwater in eastern Kentucky, where methane was detected in 78% of the sampled wells (40 of 51 wells) with 51% of wells (26 of 51 wells) exhibiting methane concentrations above 1 mg/L. The δ¹³C‐CH₄ and δ²H‐CH₄ ranged from ?84.0‰ to ?58.3‰ and from ?246.5‰ to ?146.0‰, respectively. Isotopic analysis indicated that dissolved methane was primarily microbial in origin formed through CO₂ reduction pathway. Results from this study provide a first assessment of methane in the shallow aquifers in the Berea and Rogersville play areas and can be used as a reference to evaluate potential impacts of future horizontal drilling and hydraulic fracturing activities on groundwater quality in the region.     

Long-time variation of soil CO2 fluxes at the summit crater of Vulcano (Italy)

Here, we report the first continuous data of geochemical parameters acquired directly from the active summit crater of Vulcano. This approach provides a means to better investigate deep geochemical processes associated with the degassing system of Vulcano Island. In particular, we report on soil CO₂ fluxes from the upper part of Vulcano, a closed-conduit volcano, from September 2007 to October 2010. Large variations in the soil CO₂ and plume SO₂ fluxes (order of magnitude), coinciding with other discontinuous geochemical parameters (CO₂ concentrations in fumarole gas) and physical parameters (increase of shallow seismic activity and fumarole temperatures) have been recorded. The results from this work suggest new prospects for strengthening geochemical monitoring of volcanic activity and for improving the constraints in the construction of a “geochemical model”, this being a necessary condition to better understand the functioning of volcanic systems.     

Vadose CO2 gas drives dissolution at water tables in eogenetic karst aquifers more than mixing dissolution

Most models of cave formation in limestone that remains near its depositional environment and has not been deeply buried (i.e. eogenetic limestone) invoke dissolution from mixing of waters that have different ionic strengths or have equilibrated with calcite at different _pCO₂ values. In eogenetic karst aquifers lacking saline water, mixing of vadose and phreatic waters is thought to form caves. We show here calcite dissolution in a cave in eogenetic limestone occurred due to increases in vadose CO₂ gas concentrations and subsequent dissolution of CO₂ into groundwater, not by mixing dissolution. We collected high‐resolution time series measurements (1 year) of specific conductivity (SpC), temperature, meteorological data, and synoptic water chemical composition from a water table cave in central Florida (Briar Cave). We found SpC, _pCO₂ and calcite undersaturation increased through late summer, when Briar Cave experienced little ventilation by outside air, and decreased through winter, when increased ventilation lowered cave CO_2(g) concentrations. We hypothesize dissolution occurred when water flowed from aquifer regions with low _pCO₂ into the cave, which had elevated _pCO₂. Elevated _pCO₂ would be promoted by fractures connecting the soil to the water table. Simple geochemical models demonstrate that changes in _pCO₂ of less than 1% along flow paths are an order of magnitude more efficient at dissolving limestone than mixing of vadose and phreatic water. We conclude that spatially or temporally variable vadose CO_2(g) concentrations are responsible for cave formation because mixing is too slow to generate observed cave sizes in the time available for formation. While this study emphasized dissolution, gas exchange between the atmosphere and karst aquifer vadose zones that is facilitated by conduits likely exerts important controls on other geochemical processes in limestone critical zones by transporting oxygen deep into vadose zones, creating redox boundaries that would not exist in the absence of caves. Copyright © 2014 John Wiley & Sons, Ltd.     

The effect of CO2 on the measurement of 220Rn and 222Rn with instruments utilising electrostatic precipitation

In some volcanic systems, thoron and radon activity and CO₂ flux, in soil and fumaroles, show a relationship between (²²⁰Rn/²²²Rn) and CO₂ efflux. It is theorized that deep, magmatic sources of gas are characterized by high ²²²Rn activity and high CO₂ efflux, whereas shallow sources are indicated by high ²²⁰Rn activity and relatively low CO₂ efflux. In this paper we evaluate whether the observed inverse relationship is a true geochemical signal, or potentially an analytical artifact of high CO₂ concentrations. We report results from a laboratory experiment using the RAD7 radon detector, known ²²²Rn (radon) and ²²⁰Rn (thoron), and a controllable percentage of CO₂ in the carrier gas. Our results show that for every percentage of CO₂, the ²²⁰Rn reading should be multiplied by 1.019, the ²²²Rn radon should be multiplied by 1.003 and the ²²⁰Rn/²²²Rn ratio should be multiplied by 1.016 to correct for the presence of the CO₂.     

Geologic controls on the chemical behaviour of nitrate in riverside alluvial aquifers,Korea

To investigate the origin and behaviour of nitrate in alluvial aquifers adjacent to Nakdong River, Korea, we chose two representative sites (Wolha and Yongdang) having similar land‐use characteristics but different geology. A total of 96 shallow groundwater samples were collected from irrigation and domestic wells tapping alluvial aquifers. About 63% of the samples analysed had nitrate concentrations that exceeded the Korean drinking water limit (44·3 mg l^?1 NO₃^?), and about 35% of the samples had nitrate concentrations that exceeded the Korean groundwater quality standard for agricultural use (88·6 mg l^?1 NO₃^?). Based on nitrogen isotope analysis, two major nitrate sources were identified: synthetic fertilizer (about 4‰ δ¹⁵N) applied to farmland, and animal manure and sewage (15–20‰ δ¹⁵N) originating from upstream residential areas. Shallow groundwater in the farmland generally had higher nitrate concentrations than those in residential areas, due to the influence of synthetic fertilizer. Nitrate concentrations at both study sites were highest near the water table and then progressively decreased with depth. Nitrate concentrations are also closely related to the geologic characteristics of the aquifer. In Yongdang, denitrification is important in regulating nitrate chemistry because of the availability of organic carbon from a silt layer (about 20 m thick) below a thin, sandy surface aquifer. In Wolha, however, conservative mixing between farmland‐recharged water and water coming from a village is suggested as the dominant process. Mixing ratios estimated based on the nitrate concentrations and the δ¹⁵N values indicate that water originating from the village affects the nitrate chemistry of the shallow groundwater underneath the farmland to a large extent. Copyright © 2003 John Wiley & Sons, Ltd.     

Modeling Basin- and Plume-Scale Processes of CO2 Storage for Full-Scale Deployment

Integrated modeling of basin- and plume-scale processes induced by full-scale deployment of CO₂ storage was applied to the Mt. Simon Aquifer in the Illinois Basin. A three-dimensional mesh was generated with local refinement around 20 injection sites, with approximately 30 km spacing. A total annual injection rate of 100 Mt CO₂ over 50 years was used. The CO₂-brine flow at the plume scale and the single-phase flow at the basin scale were simulated. Simulation results show the overall shape of a CO₂ plume consisting of a typical gravity-override subplume in the bottom injection zone of high injectivity and a pyramid-shaped subplume in the overlying multilayered Mt. Simon, indicating the important role of a secondary seal with relatively low-permeability and high-entry capillary pressure. The secondary-seal effect is manifested by retarded upward CO₂ migration as a result of multiple secondary seals, coupled with lateral preferential CO₂ viscous fingering through high-permeability layers. The plume width varies from 9.0 to 13.5 km at 200 years, indicating the slow CO₂ migration and no plume interference between storage sites. On the basin scale, pressure perturbations propagate quickly away from injection centers, interfere after less than 1 year, and eventually reach basin margins. The simulated pressure buildup of 35 bar in the injection area is not expected to affect caprock geomechanical integrity. Moderate pressure buildup is observed in Mt. Simon in northern Illinois. However, its impact on groundwater resources is less than the hydraulic drawdown induced by long-term extensive pumping from overlying freshwater aquifers.     

Pressure Buildup and Brine Migration During CO2 Storage in Multilayered Aquifers

Carbon dioxide injection into deep saline formations may induce large‐scale pressure increases and migration of native fluid. Local high‐conductivity features, such as improperly abandoned wells or conductive faults, could act as conduits for focused leakage of brine into shallow groundwater resources. Pressurized brine can also be pushed into overlying/underlying formations because of diffuse leakage through low‐permeability aquitards, which occur over large areas and may allow for effective pressure bleed‐off in the storage reservoirs. This study presents the application of a recently developed analytical solution for pressure buildup and leakage rates in a multilayered aquifer‐aquitard system with focused and diffuse brine leakage. The accuracy of this single‐phase analytical solution for estimating far‐field flow processes is verified by comparison with a numerical simulation study that considers the details of two‐phase flow. We then present several example applications for a hypothetical CO₂ injection scenario (without consideration of two‐phase flow) to demonstrate that the new solution is an efficient tool for analyzing regional pressure buildup in a multilayered system, as well as for gaining insights into the leakage processes of flow through aquitards, leaky wells, and/or leaky faults. This solution may be particularly useful when a large number of calculations needs to be performed, that is, for uncertainty quantification, for parameter estimation, or for the optimization of pressure‐management schemes.     

Continuum-scale convective mixing in geological CO2 sequestration in anisotropic and heterogeneous saline aquifers

Deep saline aquifers are important geological formations for CO₂ sequestration. It has been known that dissolution of CO₂ increases brine density, which results in downward density-driven convection and consequently greatly enhances CO₂ sequestration. In this study, a continuum-scale lattice Boltzmann model is used to investigate convective mixing of CO₂ in saline aquifers. It is found that increasing permeability in either the vertical or horizontal direction accelerates the development of convective mixing. In a heterogeneous aquifer, increasing heterogeneity hampers the onset of convective mixing, because the heterogeneous permeability field results in a large portion of low-velocity region which reduces the instability of the system. The critical time for the onset of instability depends mainly on the coefficient of variation (COV) of the permeability field, and is insensitive to the correlation length. This implies that within the scale of critical time, mass transport is dominated by diffusion, and thus depends mainly on fine-scale heterogeneity controlled by COV. We derived an empirical formula for estimating the critical time, which leads to good estimates for all combinations of COV and correlation length. Fingering, channeling, and dispersion are the three mechanisms for mass transport. In dispersion, dissolved mass is approximately proportional to the square root of time, while in fingering and channeling it is approximately proportional to time. Mass transport by channeling depends significantly on permeability structure, while by fingering it is controlled by gravitational instability. It is also found that larger volumes of CO₂ can be stored in heterogeneous aquifers because of higher mass dissolution rates.     

CO2 output and δ13C(CO2) from Mount Etna as indicators of degassing of shallow asthenosphere

 An estimated average CO₂ output from Etna's summit craters in the range of 13±3 Mt/a has recently been determined from the measured SO₂ output and measured CO₂/SO₂ molar ratios. To this amount the CO₂ output emitted diffusely from the soil (≈ 1 Mt/a) and the amount of CO₂ dissolved in Etna's aquifers (≈ 0.25 Mt/a) must be added. Data on the solubility of CO₂ in Etnean magmas at high temperature and pressure allow the volume of magma involved in the release of such an amount of this gas to be estimated. This volume of magma (≈ 0.7 km³/a) is approximately 20 times greater than the volume of magma erupted annually during the period 1971–1995. On the basis of C-isotopic data of CO₂ collected in the Etna area and of new hypotheses on the source of Mediterranean magmas, significant contributions of CO₂ from non-magmatic sources to the total output from Etna are unlikely. Such large outputs of CO₂ and also of SO₂ from Etna could be due to an anomalously shallow asthenosphere beneath the volcano that allows a continuous escape of gases toward the surface, even without migration of magma. Received: 7 August 1996 / Accepted: 9 November 1996     

Lower Groundwater 14C Age by Atmospheric CO2 Uptake During Sampling and Analysis

Uptake of atmospheric CO₂ during sample collection and analysis, and consequent lowering of estimated ages, has rarely been considered in radiocarbon dating of groundwater. Using field and laboratory experiments, we show that atmospheric CO₂ can be easily and rapidly absorbed in hyperalkaline solutions used for the extraction of dissolved inorganic carbon, resulting in elevated ¹⁴C measurements. Kinetic isotope fractionation during atmospheric CO₂ uptake may also result in decrease of δ¹³C, leading to insufficient corrections for addition of dead carbon by geochemical processes. Consequently, measured ¹⁴C values of groundwater should not be used for age estimation without corresponding δ¹³C values, and historical ¹⁴C data in the range of 1 to 10% modern Carbon should be re‐evaluated to ensure that samples with atmospheric contamination are recognized appropriately. We recommend that samples for ¹⁴C analysis should be collected and processed in the field and the laboratory without exposure to the atmosphere. These precautions are considered necessary even if ¹⁴C measurements are made with an accelerator mass spectrometer.     

Preliminary results of seismogeochemical research in China

Several kinds of geochemical anomaly before strong earthquakes have been observed in China since 1966. They include changes in groundwater radon levels, ion content of water (Ca⁺², Mg⁺², Cl^–, SO ₄ ^–2 , F^–), dissolved gases (H₂, CO₂), and gases escaping from the aeration zone through abandoned dry wells (Ar, N₂, CO₂). The radon anomalies may be grouped as long-term and short-term anomalies. Most of the geochemical anomalies observed are characterized by a pattern of increase. The largest amplitude recorded was 37 times the base level. Preliminary study indicates that the types of seismogeochemical anomaly observed prior to strong earthquakes depend on tectonic, geologic, lithologic, and hydrogeological conditions at the monitoring station. Results obtained from modelling experiments on the mechanisms of some anomalies are given.