The complexity of alluvial-pluvial fan depositional systems makes the detailed characterization of their heterogeneity difficult, yet such a detailed characterization is commonly needed for construction of reliable gr...The complexity of alluvial-pluvial fan depositional systems makes the detailed characterization of their heterogeneity difficult, yet such a detailed characterization is commonly needed for construction of reliable groundwater models. Traditional models mainly focus on using a single aquifer property to qualitatively or semi-quantitatively characterize the heterogeneity of aquifer, so that they are unable to quantitatively reflect the synthetic heterogeneity of all aquifer properties. In this paper, we propose the heterogeneity synthetic index （HSI） for quantitative characterization of synthetic heterogeneity of an aquifer. The proposed calculation process involves four steps： （1） estimation of the hydraulic conductivity of a sediment sample using the cloud-Markov model, （2） establishment of the sedimentary microfacies distribution model through the Markov chain, （3） characterization of the distribution model of hydrogeological parameters using the improved sequential simulation method according to the ＂facies-controlled modeling＂ technique, and （4） application of the entropy weight method to calculate the weight coefficient of the above aquifer properties. The HSI of an aquifer is calculated by superposition of these models according to the corresponding weight coefficient. This approach was applied to the Luancheng aquifer deposit in the southeast Hutuo River alluvial-pluvial fan in the North China Plain （NCP）. The results have demonstrated that aquifer 3 which was formed in the middle Pleistocene has the strongest heterogeneity, with an HSI of 0.25-0.75. Aquifer 4 formed in the early Pleistocene shows an intermediate heterogeneity, with the HSI ranging 0.35-0.75. The weakest heterogeneity was found in aquifers 1 and 2 formed in the Holocene and late Pleistocene, with HSI values of 0.40-0.75 and 0.40- 0.80, respectively. The heterogeneity of all the four aquifers is relatively strong in the radial direction of the Huai River alluvial-pluvial fan due to the abrupt change of microfac展开更多
为了研究含水层多孔介质参数非均质性,利用一系列连续的交叉孔水力试验获取含水层对于外界干扰的反应信息,应用序贯连续线性估计方法(Sequential Successive Linear Estimator)对多系列水头信息进行随机参数估计,即水力层析法。应用该...为了研究含水层多孔介质参数非均质性,利用一系列连续的交叉孔水力试验获取含水层对于外界干扰的反应信息,应用序贯连续线性估计方法(Sequential Successive Linear Estimator)对多系列水头信息进行随机参数估计,即水力层析法。应用该方法对随机产生参数的一维含水层进行了渗透系数K和储水率Ss的估算,并对估计值和真实值进行了对比,其中使用单井数据计算就可使K值的平均相对误差控制在2.67%,证明了该方法的有效性。在对某地浸采铀厂区长、宽为150m×150m的含水层进行了实例研究,使用29口井孔进行层析试验,对于该二维水平分布含水层的非均质特征进行了刻画,其中K值为0.5~1.4 m/d,Ss为0.00005/m^0.0002/m。该数据在后期的地下水污染溶质运移模拟中取得了很好的应用。作为研究地下水参数的新方法,水力层析法能够对三维分布的含水层特征进行高精度刻画,这种层析的概念和反演方法可广泛应用于环境和地球科学领域的研究。展开更多
由于地质条件的复杂性,人们所能获取的地质和水文地质资料是有限的,这就导致对水文地质条件的认识具有不确定性,其中以含水层非均质特征最为显著,这对地下水脆弱性评价显然会产生显著的影响。考虑含水层的非均质特性,提出具有非平稳随...由于地质条件的复杂性,人们所能获取的地质和水文地质资料是有限的,这就导致对水文地质条件的认识具有不确定性,其中以含水层非均质特征最为显著,这对地下水脆弱性评价显然会产生显著的影响。考虑含水层的非均质特性,提出具有非平稳随机场空间相关性的地下水脆弱性评价方法。以南京市江宁区中部地区为例,用改进的连续随机增加方法(Successive Random Additional method,简称SRA)生成了渗透系数对数(lnK),具有分维Levy运动统计特征的随机场,模拟含水层渗透系数可能的非均质空间分布,采用DRASTIC方法进行地下水脆弱性评价。结果表明由此方法生成的渗透系数场变化的程度相对传统的普通克里金方法更加剧烈,更加符合复杂分布的非平稳随机场特征,在此基础上建立的地下水脆弱性评价更加符合客观事实,丰富和发展利用随机理论解决地下水环境问题的理论和方法。展开更多
Two biodegradation models are developed to represent natural attenuation of fuel-hydrocarbon contaminants as observed in a comprehensive natural-gradient tracer test in a heterogeneous aquifer on the Columbus Air Forc...Two biodegradation models are developed to represent natural attenuation of fuel-hydrocarbon contaminants as observed in a comprehensive natural-gradient tracer test in a heterogeneous aquifer on the Columbus Air Force Base in Mississippi, USA. The first, a first-order mass loss model, describes the irreversible losses of BTEX and its individual components, i.e., benzene (B), toluene (T), ethyl benzene (E), and xylene (X). The second, a reactive pathway model, describes sequential degradation pathways for BTEX utilizing multiple electron acceptors, including oxygen, nitrate, iron and sulfate, and via methanogenesis. The heterogeneous aquifer is represented by multiple hydraulic conductivity (K) zones delineated on the basis of numerous flowmeter K measurements. A direct propagation artificial neural network (DPN) is used as an inverse modeling tool to estimate the biodegradation rate constants associated with each of the K zones. In both the mass loss model and the reactive pathway model, the biodegradation rate constants show an increasing trend with the hydraulic conductivity. The finding of correlation between biodegradation kinetics and hydraulic conductivity distributions is of general interest and relevance to characterization and modeling of natural attenuation of hydrocarbons in other petroleum-product contaminated sites.展开更多
Many parameters have been indicated crucial for the selection of a saline aquifer as a carbon dioxide(CO_(2))storage site.However,less attention has been given to the impact of heterogeneity on the performance of thes...Many parameters have been indicated crucial for the selection of a saline aquifer as a carbon dioxide(CO_(2))storage site.However,less attention has been given to the impact of heterogeneity on the performance of these storage media.Thus,the heterogeneity effect was evaluated in this paper by adopting a numerical modeling approach and the existing screening criterion developed for the aquifers was updated.The updated criterion for CO_(2)storage purpose would enhance the confidence level during the selection of deep saline aquifer and thus,help to address the climate change issue.The numerical modeling was carried out via CO_(2)STORE module of Eclipse300 Simulator to evaluate the effect of different levels of heterogeneity on CO_(2)storage potential.Different degrees of heterogeneity from homogenous systems to highly heterogeneous systems in the model were incorporated through the Lorenz coefficient.In this way,simulation of nine cases was carried out for three different aquifers with different porosity values.A comparison of these results showed that heterogeneity causes the aquifer to have lower storage capacity.On the trapping potential,dissolution trapping was significant and the amount of free gas in all cases was minimum.In addition,the aquifer with the highest level of heterogeneity(HLH)had a minimum fraction of residual trapping regardless of porosity.It was also found that final pressure at the end of 30 years is the same and high for low-level heterogeneity(LLH)and medium level heterogeneity(MLH)cases and low for HLH,while the injection rate stability duration is least for HLH and maximum for LLH.Based on the results obtained,it can be concluded that low to medium level heterogeneous aquifers with a good porosity can be a suitable choice for CO_(2)storage.展开更多
Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the reme...Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the remediation of contaminated groundwater.Aquifer heterogeneity usually leads to a distinct feature,the so-called“anomalous transport”in groundwater,which deviates from the phenomenon described by the classical advection-dispersion equation(ADE)based on Fick’s Law.Anomalous transport,also known as non-Fickian dispersion or“anomalous dispersion”in a broad sense,can explain the hydrogeological mechanism that leads to the temporally continuous deterioration of water quality and rapid spatial expansion of pollutant plumes.Contaminants enter and then are retained in the low-permeability matrix from the high-permeability zone via molecular diffusion,chemical adsorption,and other mass exchange effects.This process can be reversed when the concentration of pollutants in high-permeability zones is relatively low.The contaminants slowly return to the high-permeability zones through reverse molecular diffusion,resulting in sub-dispersive anomalous transport leading to the chronic gradual deterioration of water quality.Meanwhile,some contaminants are rapidly transported along the interconnected preferential flow paths,resulting in super-dispersive anomalous transport,which leads to the rapid spread of contaminants.Aquifer heterogeneity is also an important factor that constrains the efficacy of groundwater remediation,while the development,application,and evaluation of groundwater remediation technologies are usually based on the Fickian dispersion process predicted by the ADE equation.Comprehensive studies of the impacts of non-Fickian dispersion on contaminant transport and remediation are still needed.This article reviews the non-Fickian dispersion phenomenon caused by the heterogeneity of geological media,summarizes the processes and current understanding of contaminant migration and transformation in hi展开更多
基金supported by the Major State Basic Research Development Program(973 Program)(No.2010CB428800)
文摘The complexity of alluvial-pluvial fan depositional systems makes the detailed characterization of their heterogeneity difficult, yet such a detailed characterization is commonly needed for construction of reliable groundwater models. Traditional models mainly focus on using a single aquifer property to qualitatively or semi-quantitatively characterize the heterogeneity of aquifer, so that they are unable to quantitatively reflect the synthetic heterogeneity of all aquifer properties. In this paper, we propose the heterogeneity synthetic index （HSI） for quantitative characterization of synthetic heterogeneity of an aquifer. The proposed calculation process involves four steps： （1） estimation of the hydraulic conductivity of a sediment sample using the cloud-Markov model, （2） establishment of the sedimentary microfacies distribution model through the Markov chain, （3） characterization of the distribution model of hydrogeological parameters using the improved sequential simulation method according to the ＂facies-controlled modeling＂ technique, and （4） application of the entropy weight method to calculate the weight coefficient of the above aquifer properties. The HSI of an aquifer is calculated by superposition of these models according to the corresponding weight coefficient. This approach was applied to the Luancheng aquifer deposit in the southeast Hutuo River alluvial-pluvial fan in the North China Plain （NCP）. The results have demonstrated that aquifer 3 which was formed in the middle Pleistocene has the strongest heterogeneity, with an HSI of 0.25-0.75. Aquifer 4 formed in the early Pleistocene shows an intermediate heterogeneity, with the HSI ranging 0.35-0.75. The weakest heterogeneity was found in aquifers 1 and 2 formed in the Holocene and late Pleistocene, with HSI values of 0.40-0.75 and 0.40- 0.80, respectively. The heterogeneity of all the four aquifers is relatively strong in the radial direction of the Huai River alluvial-pluvial fan due to the abrupt change of microfac
文摘为了研究含水层多孔介质参数非均质性,利用一系列连续的交叉孔水力试验获取含水层对于外界干扰的反应信息,应用序贯连续线性估计方法(Sequential Successive Linear Estimator)对多系列水头信息进行随机参数估计,即水力层析法。应用该方法对随机产生参数的一维含水层进行了渗透系数K和储水率Ss的估算,并对估计值和真实值进行了对比,其中使用单井数据计算就可使K值的平均相对误差控制在2.67%,证明了该方法的有效性。在对某地浸采铀厂区长、宽为150m×150m的含水层进行了实例研究,使用29口井孔进行层析试验,对于该二维水平分布含水层的非均质特征进行了刻画,其中K值为0.5~1.4 m/d,Ss为0.00005/m^0.0002/m。该数据在后期的地下水污染溶质运移模拟中取得了很好的应用。作为研究地下水参数的新方法,水力层析法能够对三维分布的含水层特征进行高精度刻画,这种层析的概念和反演方法可广泛应用于环境和地球科学领域的研究。
文摘由于地质条件的复杂性,人们所能获取的地质和水文地质资料是有限的,这就导致对水文地质条件的认识具有不确定性,其中以含水层非均质特征最为显著,这对地下水脆弱性评价显然会产生显著的影响。考虑含水层的非均质特性,提出具有非平稳随机场空间相关性的地下水脆弱性评价方法。以南京市江宁区中部地区为例,用改进的连续随机增加方法(Successive Random Additional method,简称SRA)生成了渗透系数对数(lnK),具有分维Levy运动统计特征的随机场,模拟含水层渗透系数可能的非均质空间分布,采用DRASTIC方法进行地下水脆弱性评价。结果表明由此方法生成的渗透系数场变化的程度相对传统的普通克里金方法更加剧烈,更加符合复杂分布的非平稳随机场特征,在此基础上建立的地下水脆弱性评价更加符合客观事实,丰富和发展利用随机理论解决地下水环境问题的理论和方法。
文摘Two biodegradation models are developed to represent natural attenuation of fuel-hydrocarbon contaminants as observed in a comprehensive natural-gradient tracer test in a heterogeneous aquifer on the Columbus Air Force Base in Mississippi, USA. The first, a first-order mass loss model, describes the irreversible losses of BTEX and its individual components, i.e., benzene (B), toluene (T), ethyl benzene (E), and xylene (X). The second, a reactive pathway model, describes sequential degradation pathways for BTEX utilizing multiple electron acceptors, including oxygen, nitrate, iron and sulfate, and via methanogenesis. The heterogeneous aquifer is represented by multiple hydraulic conductivity (K) zones delineated on the basis of numerous flowmeter K measurements. A direct propagation artificial neural network (DPN) is used as an inverse modeling tool to estimate the biodegradation rate constants associated with each of the K zones. In both the mass loss model and the reactive pathway model, the biodegradation rate constants show an increasing trend with the hydraulic conductivity. The finding of correlation between biodegradation kinetics and hydraulic conductivity distributions is of general interest and relevance to characterization and modeling of natural attenuation of hydrocarbons in other petroleum-product contaminated sites.
基金Foundation Item：Strategic Environmental Research and Development Program （SERDP）AcknowLedgements Supports from the Strategic Environmental Research and Development Program （SERDP） subcontracted through the University of Iowa as well niversity of Waterloo are also thank two anonymous constructive and insightful as that throug acknowledged. reviewers for suggestions.
文摘Many parameters have been indicated crucial for the selection of a saline aquifer as a carbon dioxide(CO_(2))storage site.However,less attention has been given to the impact of heterogeneity on the performance of these storage media.Thus,the heterogeneity effect was evaluated in this paper by adopting a numerical modeling approach and the existing screening criterion developed for the aquifers was updated.The updated criterion for CO_(2)storage purpose would enhance the confidence level during the selection of deep saline aquifer and thus,help to address the climate change issue.The numerical modeling was carried out via CO_(2)STORE module of Eclipse300 Simulator to evaluate the effect of different levels of heterogeneity on CO_(2)storage potential.Different degrees of heterogeneity from homogenous systems to highly heterogeneous systems in the model were incorporated through the Lorenz coefficient.In this way,simulation of nine cases was carried out for three different aquifers with different porosity values.A comparison of these results showed that heterogeneity causes the aquifer to have lower storage capacity.On the trapping potential,dissolution trapping was significant and the amount of free gas in all cases was minimum.In addition,the aquifer with the highest level of heterogeneity(HLH)had a minimum fraction of residual trapping regardless of porosity.It was also found that final pressure at the end of 30 years is the same and high for low-level heterogeneity(LLH)and medium level heterogeneity(MLH)cases and low for HLH,while the injection rate stability duration is least for HLH and maximum for LLH.Based on the results obtained,it can be concluded that low to medium level heterogeneous aquifers with a good porosity can be a suitable choice for CO_(2)storage.
基金supported by the National Key R&D Program of China(Grant No.2016YFC0402806)the National Natural Science Foundation of China(Grant Nos.41931292,42007162&41722208)the Natural Science Foundation of Guangdong Province(CN)(Grant No.2020A1515010891).
文摘Natural aquifers usually exhibit complex physical and chemical heterogeneities,which are key factors complicating kinetic processes,such as contaminant transport and transformation,posing a great challenge in the remediation of contaminated groundwater.Aquifer heterogeneity usually leads to a distinct feature,the so-called“anomalous transport”in groundwater,which deviates from the phenomenon described by the classical advection-dispersion equation(ADE)based on Fick’s Law.Anomalous transport,also known as non-Fickian dispersion or“anomalous dispersion”in a broad sense,can explain the hydrogeological mechanism that leads to the temporally continuous deterioration of water quality and rapid spatial expansion of pollutant plumes.Contaminants enter and then are retained in the low-permeability matrix from the high-permeability zone via molecular diffusion,chemical adsorption,and other mass exchange effects.This process can be reversed when the concentration of pollutants in high-permeability zones is relatively low.The contaminants slowly return to the high-permeability zones through reverse molecular diffusion,resulting in sub-dispersive anomalous transport leading to the chronic gradual deterioration of water quality.Meanwhile,some contaminants are rapidly transported along the interconnected preferential flow paths,resulting in super-dispersive anomalous transport,which leads to the rapid spread of contaminants.Aquifer heterogeneity is also an important factor that constrains the efficacy of groundwater remediation,while the development,application,and evaluation of groundwater remediation technologies are usually based on the Fickian dispersion process predicted by the ADE equation.Comprehensive studies of the impacts of non-Fickian dispersion on contaminant transport and remediation are still needed.This article reviews the non-Fickian dispersion phenomenon caused by the heterogeneity of geological media,summarizes the processes and current understanding of contaminant migration and transformation in hi
