Litang Hu

Field-based simulation of a demonstration site for carbon dioxide sequestration in low-permeability saline aquifers in the Ordos Basin, China

Saline formations are considered to be candidates for carbon sequestration due to their great depths, large storage volumes, and widespread occurrence. However, injecting carbon dioxide into low-permeability reservoirs is challenging. An active demonstration project for carbon dioxide sequestration in the Ordos Basin, China, began in 2010. The site is characterized by a deep, multi-layered saline reservoir with permeability mostly below 1.0u2009×u200910−14xa0m2. Field observations so far suggest that only small-to-moderate pressure buildup has taken place due to injection. The Triassic Liujiagou sandstone at the top of the reservoir has surprisingly high injectivity and accepts approximately 80xa0% of the injected mass at the site. Based on these key observations, a three-dimensional numerical model was developed and applied, to predict the plume dynamics and pressure propagation, and in the assessment of storage safety. The model is assembled with the most recent data and the simulations are calibrated to the latest available observations. The model explains most of the observed phenomena at the site. With the current operation scheme, the CO2 plume at the uppermost reservoir would reach a lateral distance of 658xa0m by the end of the project in 2015, and approximately 1,000xa0m after 100xa0years since injection. The resulting pressure buildup in the reservoir was below 5xa0MPa, far below the threshold to cause fracturing of the sealing cap (around 33xa0MPa).RésuméLes formations salines sont considérées comme étant de bons candidats pour la séquestration du carbone, du fait de leurs grandes profondeurs, de leurs importants volumes de stockage, et de leur présence sur de grandes étendues. Cependant, l’injection du CO2 au sein de réservoirs de faible conductivité hydraulique constitue un défi. Un projet de démonstrateur pour la séquestration du CO2 dans le bassin de l’Ordos, en Chine, a débuté en 2010. Le site est caractérisé par un réservoir salin multicouche profond, avec une perméabilité généralement inférieure à 1.0•10-14 m2. Jusqu’à maintenant, les observations de terrain indiquent que seules des pressions faibles à modérées ont été induites par l’injection. Le grès triasique de Liujiagou, situé au toit du réservoir, est caractérisé par une capacité d’injection étonnamment élevée et accepte environ 80 % de la masse injectée sur le site. Un modèle numérique tri-dimensionnel a été développé à partir de ces observations clefs et appliqué, pour prédire les dynamiques du panache et la propagation de la pression, et évaluer la sécurité du stockage. Le modèle est assemblé avec les données les plus récentes et les simulations ont été calées avec les dernières observations disponibles. Le modèle explique l’essentiel des phénomènes observés sur le site. Avec le programme d’opération actuel, le panache de CO2 au toit du réservoir atteindrait latéralement une distance de 658 m à la fin du projet en 2015, et environ 1000 m après 100 ans à partir de l’injection. La pression résultante au sein du réservoir était inférieure à 5 MPa, nettement en-dessous du seuil de fracturation de la formation de scellement du réservoir (environ 33 MPa).ResumenLas formaciones salinas son consideradas candidatas para el secuestro de carbono debido a su existencia en grandes profundidades, grandes volúmenes de almacenamiento y presencia generalizada. Sin embargo, la inyección de dióxido de carbono en reservorios de baja permeabilidad es un desafío. Un proyecto de demostración activa, para el secuestro de dióxido de carbono en la cuenca de Ordos, China, se inició en 2010. El sitio se caracteriza por un reservorio salino multicapa profundo con permeabilidad mayormente debajo de 1.0u2009×u200910−14xa0m2. Las observaciones de campo hasta el momento sugieren que sólo el pequeño a moderado aumento de presión ha tenido lugar debido a la inyección. La arenisca triásica en el techo del reservorio tiene sorpresivamente una alta inyectividad y acepta aproximadamente el 80xa0% de la masa inyectada en el sitio. Sobre la base de estas observaciones claves, se desarrolló y aplicó un modelo numérico, para predecir la dinámica y presión de la pluma de propagación, y para la evaluación de la seguridad del almacenamiento. El modelo se ensambla con los datos más recientes y las simulaciones son calibradas con las últimas observaciones disponibles. El modelo explica la mayoría de los fenómenos observados en el sitio. Con el esquema de operación actual, la pluma de CO2 en el reservorio superior podría alcanzar una distancia lateral de 658xa0m para el final del proyecto en 2015, y aproximadamente 1,000xa0m después de 100 años de inyección. La acumulación de presión resultante en el depósito estaba por debajo 5xa0MPa, muy por debajo del umbral para provocar la fractura de la capa de cierre (alrededor de 33xa0MPa).摘要咸水层由于其深度大、储存容积大及广泛分布通常被选为碳封存的候选地。然而,把二氧化碳注入到低透水性的储层中是一项挑战。2010年,在中国鄂尔多斯盆地开展了二氧化碳封存示范项目。场地为一个深的、多层的咸水层,渗透性大部分低于1.0u2009×u200910−14 米2。到目前为止的野外观测结果显示,由于二氧化碳注入,只出现了小到中的压力抬升。储层之上的三叠纪刘家沟砂岩层具有惊人高的吸气量,接受了场地大约80%的注入量。基于这些关键的观测结果,建立和应用了三维数值模型,用来预测压力传播的羽体动态变化及用于储存安全的评价。模型采用最新的数据,针对最新现有的观测结果对模型进行了校准。模型能够解释场地所观测到的大部分现象。根据目前运行计划,储层最上面的二氧化碳羽在2015年项目结束时将侧向到达658米的距离,注入100年后大约到达1,000米的距离。所导致的储层内压力抬升低于5 MPa,远低于引起密封盖层破裂的阈值(33 MPa左右)。ResumoFormações salinas são consideradas como candidatas para sequestro de carbono devido a sua grande profundidade, grande volume de armazenamento e ampla ocorrência. Entretanto, injetar dióxido de carbono em reservatórios de baixa permeabilidade é desafiador. Um projeto de demonstração ativa para sequestro de dióxido de carbono na Bacia de Ordos, China, começou em 2010. A área é caracterizada como um reservatório salino profundo, de múltiplas camadas com permeabilidade, na maioria das vezes, abaixo de 1.0u2009×u200910−14xa0m2. Observações de campo sugerem até o momento que apenas um pequeno a moderado aumento de pressão ocorreu devido à injeção. O arenito Triássico Liujiagou, no topo do reservatório, possui uma surpreendente alta injectividade e aceita aproximadamente 80xa0% da massa injetada na área. Baseado nestas observações, um modelo numérico tridimensional foi desenvolvido e aplicado para prever a dinâmica da pluma, a propagação da pressão e avaliar a segurança do armazenamento. O modelo é elaborado com os dados mais recentes e as simulações são calibradas com as últimas observações disponíveis. O modelo explica a maioria dos fenômenos observados na área. Com o plano atual de operação, a pluma de CO2 no reservatório superior irá alcançar a distância de 658xa0m no final do projeto em 2015 e, aproximadamente, 1,000xa0m após 100 anos de injeção. O aumento de pressão resultante no reservatório foi abaixo de 5xa0MPa, muito abaixo do limite de fraturamento da camada selante (aproximadamente 33xa0MPa).

Calibration of a large-scale groundwater flow model using GRACE data: a case study in the Qaidam Basin, China

Traditional numerical models usually use extensive observed hydraulic-head data as calibration targets. However, this calibration process is not applicable in remote areas with limited or no monitoring data. This study presents an approach to calibrate a large-scale groundwater flow model using the monthly Gravity Recovery and Climate Experiment (GRACE) satellite data, which have been available globally on a spatial grid of 1° in the geographic coordinate system since 2002. A groundwater storage anomaly isolated from the terrestrial water storage (TWS) anomaly is converted into hydraulic head at the center of the grid, which is then used as observed data to calibrate a numerical model to estimate aquifer hydraulic conductivity. The aquifer system in the remote and hyperarid Qaidam Basin, China, is used as a case study to demonstrate the applicability of this approach. A groundwater model using FEFLOW is constructed for the Qaidam Basin and the GRACE-derived groundwater storage anomaly over the period 2003–2012 is included to calibrate the model, which is done using an automatic estimation method (PEST). The calibrated model is then run to output hydraulic heads at three sites where long-term hydraulic head data are available. The reasonably good fit between the calculated and observed hydraulic heads, together with the very similar groundwater storage anomalies from the numerical model and GRACE data, demonstrate that this approach is generally applicable in regions of groundwater data scarcity.Résuméu2009Les modèles numériques traditionnels utilisent de nombreuses données piézométriques observées pour leur calage. Toutefois, cette procédure de calage n’est pas applicable pour les régions éloignées où les mesures sont rares ou inexistantes. Cette étude présente une approche pour caler un modèle d’écoulement souterrain à grande échelle en utilisant les données mensuelles du satellite d’enregistrement gravimétrique et d’étude de climat (GRACE), disponibles sur une grille spatiale de 1° dans le système de coordonnées géographiques depuis 2002. Une anomalie de stockage d’eau souterraine isolée de l’anomalie terrestre de stockage d’eau (TWS) est convertie en cote piézométrique au centre de la maille de la grille, et est utilisée comme donnée d’observation pour caler un modèle numérique afin d’estimer la conductivité hydraulique de l’aquifère. Le système aquifère du bassin éloigné et hyperaride de Qaidam, Chine, est utilisé comme cas d’étude pour démontrer la faisabilité de cette approche. FEFLOW est utilisé pour modéliser les écoulements souterrains du bassin de Qaidam. L’anomalie de stockage d’eau souterraine déduite des données de GRACE sur la période 2003–2012 est utilisée pour caler le modèle, à partir d’une méthode d’estimation automatique des paramètres (PEST). Le modèle calé simule ensuite les niveaux piézométriques de trois sites pour lesquels de longues séries chronologiques piézométriques observées sont disponibles. La relativement bonne correspondance entre les niveaux piézométriques calculés et observés, ainsi que la similitude entre les anomalies de stockage d’eau souterraine du modèle numérique et de celles de GRACE, démontrent que cette approche est généralement applicable pour les régions pauvres en données sur les eaux souterraines.ResumenLos modelos numéricos tradicionales habitualmente utilizan una gran cantidad de datos observados de la carga hidráulica como patrones de calibración. Sin embargo, este proceso de calibración no es aplicable en áreas remotas con datos de monitoreo limitados o no existentes. Este estudio presenta un enfoque para calibrar un modelo de flujo de agua subterránea a gran escala usando los datos satelitales mensuales de Gravity Recovery and Climate Experiment (GRACE), que han estado disponibles globalmente a nivel mundial con una malla espacial de 1° en el sistema de coordenadas geográficas desde 2002. Una anomalía aislado del almacenamiento de agua subterránea a partir de la anomalía del almacenamiento de agua terrestre (TWS) fue convertida en una carga hidráulica en el centro de la malla, la cual es luego usada como un dato observado para calibrar un modelo numérico para estimar la conductividad hidráulica del acuífero. Se usó un sistema acuífero en la remota e hiperárida cuenca de Qaidam, China, como un caso de estudio para demostrar la aplicabilidad de este enfoque. Se construyó un modelo de agua subterránea usando FEFLOW para la cuenca de Qaidam y la anomalía del almacenamiento de agua subterránea proveniente del GRACE durante el período 2003–2012 se incluyó para calibrar el modelo, el cual es usado como un método de estimación automático (PEST). El modelo calibrado es luego corrido para obtener las cargas hidráulicas de salida en tres sitios donde los datos a largo plazo de las cargas hidráulicas están disponibles. El razonable buen ajuste entre las cargas hidráulicas calculadas y observadas, conjuntamente con anomalías muy similares del almacenamiento del agua subterránea a partir del modelo numérico y de los datos GRACE, demostraron que esta aproximación es generalmente aplicable en regiones que presentan escasez de datos de agua subterránea.摘要传统的地下水数值模型采用大量的地下水监测数据作为拟合目标。然而,这种方法在有很少甚至没有地下水观测数据的偏远地区难以应用。本研究提出了一种利用重力恢复和气候实验卫星数据 (GRACE)校准大尺度地下水流数值模型的方法。该数据是自2002年以来发布,其时间尺度为1个月,空间尺度为1度,可免费下载的。提出的方法中,先将陆地水储量(TWS) 推算的地下水储量变异数据转化为相应网格中心位置的水头值,然后将这些值作为数值模型参数率定时的拟合目标。本研究以偏远的极端干旱的中国柴达木盆地为例来展示该方法的可行性。本研究利用FEFLOW软件在柴达木盆地建立了地下水流数值模型,并用2003–2012年反演的地下水储量变异数据用于模型校准,其中采用了自动参数估计方法 (PEST)。经过校准的模型模拟的与GRACE反演的地下水储量变异数据具有较好的相似性,而且在三个具有长期地下水位观测位置的模拟和监测值具有吻合较好。这些结果展示了本研究提出的方法可以用于地下水数据缺乏地区的地下水模型校准。ResumoOs modelos numéricos tradicionais normalmente usam longas séries de dados de carga hidráulica como alvos de calibração. No entanto, esse processo de calibração não é aplicável em áreas remotas com dados de monitoramento limitados ou ausentes. Este trabalho apresenta uma abordagem para calibrar um modelo de fluxo subterrâneo de larga escala usando os dados do satélite GRACE, os quais são disponibilizados globalmente numa grade espacial de 1° no sistema de coordenadas geográficas desde 2002. Uma anomalia no armazenamento de água subterrânea isolada da anomalia de armazenamento terrestre (AAT, Armazenamento de Água Terrestre) é convertida em carga hidráulica no centro da grade, que é então usada como dado observado para calibrar um modelo numérico para estimar a condutividade hidráulica do aquífero. O sistema aquífero na remota e hiperárida bacia do Qaidam, China, é usado como estudo de caso para demonstrar a aplicabilidade dessa abordagem. O FEFLOW foi usado para construir um modelo de água subterrânea para a bacia do Qaidam e a anomalia de armazenamento subterrâneo derivada do GRACE referente ao período 2003–2012 é incluída para calibrar o modelo por meio de um método automático de estimativa (PEST). O modelo calibrado é então executado para fornecer cargas hidráulicas em três áreas onde dados de carga hidráulica de longo prazo estão disponíveis. Um ajuste razoavelmente bom entre as cargas observadas e calculadas, juntamente com as anomalias do modelo numérico e dos dados do GRACE bastante similares, demonstram que essa abordagem é, em geral, aplicável em regiões com escassez de dados.

Analytical studies on transient groundwater flow induced by land reclamation

[1]xa0In many coastal areas, land has been reclaimed by dumping fill materials into the sea. Land reclamation may have a significant effect on groundwater regimes, especially when the reclamation is at large scale. Analytical studies on the impact of land reclamation on steady-state ground water flow conditions were conducted previously, but transient analytical solutions are not yet available. Transient analytical solutions are derived to illustrate the temporal change of groundwater systems in response to land reclamation using two hypothetical models: a hillside aquifer and an oceanic elongated island. The analytical solutions show that when time is short, the water level in the reclaimed area increases significantly after reclamation while that in the original aquifer remains almost unchanged. When time is great, the change of water level in the reclaimed site becomes small but the increase of water level propagates into the original aquifer. For the specific parameters and aquifer geometry used in the examples, it takes at least over 100 years for the whole system to approach a new equilibrium. The island example demonstrates that land reclamation on one side of the island will eventually modify the groundwater regimes over the entire island, including the water level, water divide, and submarine groundwater discharge. The degree of the modification of the groundwater system and the time required for the system to approach a new equilibrium depend mainly on the hydraulic conductivity and storativity of the fill materials and the reclamation length. It is suggested that for a large reclamation project, the response of the groundwater regime to reclamation should be studied in detail to evaluate the long-term change of the flow system and the consequent environmental and engineering impacts.

Analytical Methods for Transient Flow to a Well in a Confined-Unconfined Aquifer

Concurrent existence of confined and unconfined zones of an aquifer can arise owing to ground water withdrawal by pumping. Using Girinskiis potential function, Chen (1974, 1983) developed an approximate analytical solution to analyze transient ground water flow to a pumping well in an aquifer that changes from an initially confined system to a system with both unconfined and confined regimes. This article presents the details of the Chen model and then compares it with the analytical model developed by Moench and Prickett (1972) for the same problem. Hypothetical pumping test examples in which the aquifer undergoes conversion from confined to water table conditions are solved by the two analytical models and also a numerical model based on MODFLOW. Comparison of the results suggests that the solutions of the Chen model give better results than the Moench and Prickett model except when the radial distance is very large or aquifer thickness is large compared with drawdown.

User's Guide of TOUGH2-EGS. A Coupled Geomechanical and Reactive Geochemical Simulator for Fluid and Heat Flow in Enhanced Geothermal Systems Version 1.0

TOUGH2-EGS is a numerical simulation program coupling geomechanics and chemical reactions for fluid and heat flows in porous media and fractured reservoirs of enhanced geothermal systems. The simulator includes the fully-coupled geomechanical (THM) module, the fully-coupled geochemical (THC) module, and the sequentially coupled reactive geochemistry (THMC) module. The fully-coupled flow-geomechanics model is developed from the linear elastic theory for the thermo-poro-elastic system and is formulated with the mean normal stress as well as pore pressure and temperature. The chemical reaction is sequentially coupled after solution of flow equations, which provides the flow velocity and phase saturation for the solute transport calculation at each time step. In addition, reservoir rock properties, such as porosity and permeability, are subjected to change due to rock deformation and chemical reactions. The relationships between rock properties and geomechanical and chemical effects from poro-elasticity theories and empirical correlations are incorporated into the simulator. This report provides the user with detailed information on both mathematical models and instructions for using TOUGH2-EGS for THM, THC or THMC simulations. The mathematical models include the fluid and heat flow equations, geomechanical equation, reactive geochemistry equations, and discretization methods. Although TOUGH2-EGS has the capability for simulating fluid and heat flows coupled morexa0» with both geomechanical and chemical effects, it is up to the users to select the specific coupling process, such as THM, THC, or THMC in a simulation. There are several example problems illustrating the applications of this program. These example problems are described in details and their input data are presented. The results demonstrate that this program can be used for field-scale geothermal reservoir simulation with fluid and heat flow, geomechanical effect, and chemical reaction in porous and fractured media. «xa0less

Evaluation of Groundwater Storage Variations in Northern China Using GRACE Data

Dynamic change of groundwater storage is one of the most important topics in the sustainable management of groundwater resources. Groundwater storage variations are firstly isolated from the terrestrial water storage change using the Global Land Data Assimilation System (GLDAS). Two datasets are used: annual groundwater resources and groundwater storage changes estimated from point-based groundwater level data in observation wells. Results show that the match between the GRACE-derived groundwater storage variations and annual water resources variation is not good in six river basins of Northern China. However, it is relatively good between yearly GRACE-derived groundwater storage data and groundwater storage change dataset in Huang-Huai-Hai Plain and the Song-Liao Plain. The mean annual depletion rate of groundwater storage in the Northern China was approximately 1.70 billion m3u2009yr−1 from 2003 to 2012. In terms of provinces, the yearly depletion rate is higher in Jing-Jin-Ji (Beijing, Tianjin, and Hebei province) and lowest in Henan province from 2003 to 2012, with the rate of 0.70 and 0.21u2009cmu2009yr−1 Equivalent Water Height (EWH), respectively. Different land surface models suggest that the patterns from different models almost remain the same, and soil moisture variations are generally bigger than snow water equivalent variations.

Numerical studies on the influences of the South-to-North Water Transfer Project on groundwater level changes in the Beijing Plain, China

College of Water Sciences, Beijing Normal University, Beijing 100875, China Beijing Key Laboratory of Urban Hydrological Cycle and Sponge City Technology, Beijing 100875, China Engineering Research Center of Groundwater Pollution Control and Remediation of Ministry of Education, Beijing 100875, China Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, FL, USA Correspondence Litang Hu, College of Water Sciences, Beijing Normal University, Beijing 100875, China. Email: litanghu@bnu.edu.cn

Numerical studies of CO2 and brine leakage into a shallow aquifer through an open wellbore

Industrial-scale geological storage of CO2 in saline aquifers may cause CO2 and brine leakage from abandoned wells into shallow fresh aquifers. This leakage problem involves the flow dynamics in both the wellbore and the storage reservoir. T2Well/ECO2N, a coupled wellbore-reservoir flow simulator, was used to analyze CO2 and brine leakage under different conditions with a hypothetical simulation model in water-CO2-brine systems. Parametric studies on CO2 and brine leakage, including the salinity, excess pore pressure (EPP) and initially dissolved CO2 mass fraction, are conducted to understand the mechanism of CO2 migration. The results show that brine leakage rates increase proportionally with EPP and inversely with the salinity when EPP varies from 0.5 to 1.5xa0MPa; however, there is no CO2 leakage into the shallow freshwater aquifer if EPP is less than 0.5xa0MPa. The dissolved CO2 mass fraction shows an important influence on the CO2 plume, as part of the dissolved CO2 becomes a free phase. Scenario simulation shows that the gas lifting effect will significantly increase the brine leakage rate into the shallow freshwater aquifer under the scenario of 3.89% dissolved CO2 mass fraction. The equivalent porous media (EPM) approach used to model the wellbore flow has been evaluated and results show that the EPM approach could either under- or over-estimate brine leakage rates under most scenarios. The discrepancies become more significant if a free CO2 phase evolves. Therefore, a model that can correctly describe the complex flow dynamics in the wellbore is necessary for investigating the leakage problems.RésuméLe stockage géologique de C02 à l’échelle industrielle dans des aquifères salins peut entraîner des fuites de CO2 et de saumure à partir de puits abandonnés vers des aquifères peu profonds. Ce problème de fuite concerne la dynamique des flux aussi bien dans le puits de forage que dans le réservoir de stockage. T2Well / ECO2N, un simulateur d’écoulement couplant le puits de forage au réservoir, a été utilisé pour analyzer les fuites de CO2 et de saumure pour différentes conditions avec un modèle de simulation hypothétique de systèmes eau-CO2-saumure. Des études paramétriques sur les fuites de CO2 et de saumure, y compris la salinité, la pression interstitielle excédentaire (PIE) et la fraction massique initiale de CO2 dissous, sont menées afin de comprendre le mécanisme de migration du CO2. Les résultats montrent que les taux de fuite de saumure augmentent de manière proportionnelle avec la PIE et inversement avec la salinité lorsque la PIE varie de 0.5 à 1.5xa0MPa; cependant, il n’y a pas de fuite de CO2 dans l’aquifère peu profond d’eau douce si la PIE est. inférieure à 0.5xa0MPa. La fraction massique de CO2 dissous montre une influence importante sur le panache de CO2, une partie du CO2 dissous devenant une phase libre. La simulation de scénario montre que l’effet d’éjection du gaz augmentera de manière considérable le taux de fuite de saumure dans l’aquifère peu profond d’eau douce pour le scénario de 3.89% de fraction massique de CO2 dissous. L’approche des milieux poreux équivalent (MPE) utilisée pour modéliser l’écoulement au puits a été évaluée et les résultants montrent que l’approche MPE pourrait sous-estimer ou surestimer les taux de fuite de saumure pour la plupart des scénarios. Les écarts deviennent plus significatifs si une phase de CO2 libre évolue. Par conséquent, un modèle capable de décrire correctement la dynamique des écoulements complexes dans le puits de forage est. nécessaire pour étudier les problèmes de fuite.ResumenEl almacenamiento geológico a escala industrial del CO2 en los acuíferos salinos puede causar fugas de CO2 y de salmuera desde los pozos abandonados a los acuíferos de agua dulce poco profundos. Este problema de fugas implica una dinámica de flujo tanto en el pozo como en el reservorio. El T2Well / ECO2N es un simulador acoplado de flujo de pozo y del reservorio, se usó para analizar las fugas de CO2 y salmuera en diferentes condiciones con un modelo hipotético de simulación en los sistemas de agua-CO2-salmuera. Los estudios paramétricos sobre fugas de CO2 y salmuera, que incluyen la salinidad, la presión poral en exceso (EPP) y la fracción de masa de CO2 inicialmente disuelta, se realizan para comprender el mecanismo de migración de CO2. Los resultados muestran que las tasas de fuga de salmuera aumentan proporcionalmente con la EPP e inversamente con la salinidad cuando la EPP varía de 0.5 a 1.5xa0MPa; sin embargo, no hay fuga de CO2 en el acuífero de agua dulce poco profunda si el EPP es inferior a 0.5xa0MPa. La fracción de masa de CO2 disuelta muestra una influencia importante en la pluma de CO2, ya que parte del CO2 disuelto se convierte en una fase libre. La simulación del escenario muestra que el efecto de elevación del gas aumentará significativamente la tasa de fuga de salmuera en el acuífero superficial de agua dulce en el escenario de la fracción de masa de CO2 disuelto del 3.89%. Se evaluó el enfoque de medios porosos equivalentes (EPM) utilizado para modelar el flujo del pozo y los resultados muestran que el enfoque EPM podría subestimar o sobreestimar las tasas de fuga de salmuera en la mayoría de los escenarios. Las discrepancias se vuelven más significativas si evoluciona una fase de CO2 libre. Por lo tanto, un modelo que puede describir correctamente la compleja dinámica de flujo en el pozo es necesario para investigar los problemas de fugas.摘要咸水层中工业规模化的CO2地质封存可能会引起CO2和咸水沿废弃井向浅层含水层泄露的问题。泄露的过程不仅包括流体在储层中的运动,还包括其在井管中的运移。本研究基于理想模型,采用耦合的井管-储层数值模拟器(T2Well/ECO2N)分析研究了水-CO2-盐水系统中CO2和盐水在不同情景下的泄露规律。设计情景包括盐度、超孔隙压力和初始CO2质量分数等参数的组合。结果显示当超孔隙压力在0.5~1.5xa0MPa范围时,CO2和盐水的泄露速率与超孔隙压力成正比,与盐度成反比;当超孔隙压力小于0.5xa0MPa时,CO2和盐水无法进入浅层含水层。因为部分溶解CO2可能转变为游离态,溶解CO2的质量分数对浅层含水层中CO2污染羽的形态具有重要影响。模拟结果也显示,当溶解CO2的质量分数为3.89%时气顶效应将使盐水向浅层含水层的泄露速率大为增加。本研究同时对等效渗透率方法进行了评价研究,结果显示该方法模拟的盐水泄漏速率与T2Well/ECO2N模拟的结果存在较大差异,如果有游离态CO2出现,差异尤为明显。因此,准确模拟井管中流体动态变化的模型对于研究CO2泄露问题非常有必要。ResumoArmazenamento geológico de CO2 em escala industrial em aquíferos salinos pode causar fuga de CO2 e salmoura de poços abandonados para dentro de aquíferos rasos de água doce. Esse problema de fuga envolve a dinâmica do fluxo em ambos poço e reservatório de armazenamento. T2Well/ECO2N, um simulador de fluxo acoplado poço-reservatório, foi utilizado para analisar a fuga de CO2 e salmoura sob diferentes condições com um modelo de simulação hipotético de sistemas água-CO2-salmoura. Estudos paramétricos sob a fuga de CO2 e salmoura, incluindo salinidade, excesso de pressão no poro (EPP) e fração da massa de CO2 inicialmente dissolvido, são conduzidos para entender o mecanismo de migração do CO2. Os resultados mostram que as taxas de fuga de salmoura aumentam proporcionalmente com EPP e inversamente com a salinidade quando EPP varia de 0.5 a 1.5xa0MPa; entretanto, não há fuga de CO2 para aquíferos rasos de água doce se EPP é menor que 0.5xa0MPa. A fração de massa de CO2 dissolvida apresenta uma influência importante na pluma de CO2, como parte do CO2 apresenta-se em fase livre. A simulação de cenários mostrou que o efeito de gás ascendente aumentará significativamente a razão de fuga de salmoura na direção do aquífero raso de água doce sob o cenário de 3.89% de fração de massa dissolvida de CO2. A abordagem do meio poroso equivalente (MPE) usada para modelar o fluxo do poço foi avaliada e os resultados mostraram que a abordagem do MPE pode tanto sub quanto sobrestimar as taxas de fuga de salmoura sob a maioria dos cenários. As discrepâncias tornaram-se mais significativas se uma fase livre de CO2 desenvolver-se. Por fim, um modelo que pode descrever corretamente a dinâmica do fluxo no poço se faz necessária para investigação e problemas de fuga.

Suitability for developing riverside groundwater sources along Songhua River, Northeast China

ABSTRACT Riverbank filtration is a natural water treatment technology that consists of extracting water from rivers by pumping wells located in the adjacent alluvial aquifer. It is vital to choose the most appropriate from multiple potential candidate sites, which is a complex procedure and seldom paid attention to. In this study, a method system including multicriteria evaluation indexes was developed with which the suitability of bank filtration along the Songhua River of China for developing riverside groundwater sources was assessed. The system was comprised of main suitability indexes for water quantity, water quality, interaction intensity between surface water and groundwater, and the exploitation condition of aquifer condition, weights of which were determined by specialist marking methods. Based on this assessment system, the suitability of the study area was divided into five grades. Results show that riversides along Lalin River, Hulan River, and the middle part of Songhua River are suitable for developing riverside groundwater sources.

Radionuclide transport model for risk evaluation of high-level radioactive waste in Northwestern China

ABSTRACT The proper disposal of high-level radioactive waste (HLRW) is highly challenging. Numerical simulations are helpful methods of evaluating the risks of radionuclide transport. This paper examines the hydrogeological conditions of a prospective HLRW repository in China. A regional radionuclide transport model is first constructed using the TOUGH2-MP/EOS7R module at a site in northwestern China to evaluate radionuclide transport behavior. A flow model calibration under a steady state shows that the simulated and observed hydraulic heads match well. Hypothetical radionuclides (90Sr, 137Cs, 235U and 239Pu) are assumed to be instantaneously released at three locations with large groundwater velocities. Transport modeling shows that 235U is the most sensitive element and has the plume size (2400 m) after 10,000 years. Sensitivity analyses of parameters, including the permeability, distribution coefficient and diffusion coefficient, are carried out. The results show that the distribution coefficient is the most critical parameter for nuclide transport. These findings will provide a preliminary reference for the radionuclide migration process at a prospective HLRW disposal site, which could be informative for safety analyses and further transport in and around the repository system.