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Abstract The impact of CO 2 leakage from underground storage formations on shallow water resources is a concerning aspect in CO 2 capture and storage (CCS) risk assessment. In Campo de Calatrava region (Spain), natural CO 2 fluxes from the Earth’s mantle interact with shallow aquifers, resulting in significant changes in their physical and chemical properties. The resultant water is slightly acidic (pH 5.9-6.4), oxidizing, and enriched in iron (up to 6.1×10 -4 mol·L -1 ) and other metals usually found at trace concentrations. Thermodynamic calculations reveal that aqueous Fe(III) carbonate complexes play an important role in the persistence of this high concentration of iron and trace metals in solution.

Abstract A shallow CO2 injection experiment was conducted in an unconfined, unconsolidated siliclastic aquifer in western Denmark. The aims were to test injection and sampling systems, confirm the conceptual hydrogeological site model and determine the aquifers potential geochemical response to a larger scale, sustained CO2 injection in order to finalize design of the main release experiment. Food grade CO2 (45 kg in 48 h) was injected at 10 m depth into glacial sand and water chemistry subsequently monitored. Results indicate the injection system effectively delivered CO2 gas into the glacial sand layer where it dissolved and moved with advective flow. Dissolved CO2 was not detected in the aeolian sand (0–5 m depth) indicating prevention of migration due to permeability heterogeneities. Dissolved CO2 in the glacial sand (5–10 m depth) created a plume of depressed pH (5.6–4.7), elevated EC (166–304 μS/cm) and concurrent increases in dissolved ion concentrations. EC was the most effective indicator for presence of dissolved CO2. Ionic concentration changes were generally slight with increases in Al, Ba, K, Na, Mg, Si, Sr and Zn forming the major changes. Water quality was not significantly affected and risks from small scale, short duration CO2 contamination appear minimal for this geological setting.

La contaminación y la sobreexplotación de los acuíferos subterráneos y las aguas superficiales han llevado a una disminución de la calidad y la disponibilidad de los recursos hídricos naturales en muchas regiones. Esta situación ha llevado a un aumento de los sólidos disueltos totales (SDT) más allá de los estándares y facilita la acumulación de metales tóxicos y otros problemas como la tinción y/o la precipitación. Una de las opciones de tratamiento para una solución disuelta total elevada es la desalinización mediante un sistema de ósmosis inversa impulsado por energía solar. La parte norte de Etiopía tiene una temporada de lluvias corta y un clima seco prolongado con radiación de cielo despejado. La radiación solar oscila entre 5,46 kWh/m 2 /día en agosto a 6,82 kWh/m 2 /día en abril, con un promedio de 6,09 kWh/m 2 /día. Este documento trata sobre la aplicación de la ósmosis inversa, impulsada por un sistema de desalinización que utiliza energía solar, para suministrar agua potable a las zonas rurales del norte de Etiopía. La ósmosis inversa debido a su bajo consumo de energía es una de las mejores alternativas de desalinización. El sistema de ósmosis inversa alimentado por energía solar se desarrolló e instaló en la Universidad de Mekelle. Los componentes principales son paneles fotovoltaicos, dos alimentados por CC bombas, filtros de carbón y medidores de flujo. El sistema está diseñado para funcionar en una potencia, flujo y presión variables teniendo en cuenta la irradiancia que varía naturalmente a lo largo del día. Se analiza todo el proceso de mediciones del potencial de irradiación, la cantidad de energía generada con el panel solar y la cantidad de TDS. El agua de alimentación con TDS casi constante de alrededor de 2800 ppm del área de estudio se ha reducido a TDS bastante constante de aproximadamente 100 ppm después de la desalinización. La capacidad promedio de desalinización del sistema es de 50 litros por hora. La pollution et la surexploitation des nappes phréatiques et des eaux de surface ont entraîné une diminution de la qualité et de la disponibilité des ressources naturelles en eau dans de nombreuses régions. Cette situation a entraîné une augmentation des solides dissous totaux (TDS) au-delà des normes et facilite l'accumulation de métaux toxiques et d'autres problèmes tels que la coloration et/ou les précipitations. L'une des options de traitement pour une solution dissoute totale élevée est le dessalement à l'aide d'un système d'osmose inverse à énergie solaire. La partie nord de l'Éthiopie a une courte saison des pluies et un long temps sec avec un rayonnement du ciel clair. Le rayonnement solaire varie de 5,46 kWh/m 2 /jour en août à 6,82 kWh/m 2 /jour en avril, avec une moyenne de 6,09 kWh/m 2 /jour. Ce document traite de l'application de l'osmose inverse, entraînée par un système de dessalement utilisant l'énergie solaire, pour fournir de l'eau potable sûre aux zones rurales du nord de l'Éthiopie. L'osmose inverse en raison de sa faible consommation d'énergie est l'une des meilleures alternatives de dessalement. Un système d'osmose inverse à énergie solaire a été développé et installé à l'Université Mekelle. Les principaux composants sont des panneaux photovoltaïques, deux alimentés en CC pompes, filtres à charbon et débitmètres. Le système conçu pour fonctionner avec une puissance, un débit et une pression variables compte tenu de l'irradiance naturellement variable tout au long de la journée. L'ensemble du processus de mesure du potentiel d'irradiation, de la quantité d'énergie générée à l'aide du panneau solaire et de la quantité de TDS est discuté. L'eau d'alimentation avec un TDS presque constant autour de 2800 ppm de la zone d'étude a été réduite à un TDS assez constant d'environ 100 ppm après dessalement. La capacité moyenne de dessalement du système est de 50 litres par heure. Pollution and over exploitation of groundwater aquifer and surface water have led to a decrease of quality and availability of natural water resource in many regions.This situation has led to elevated total dissolved solids (TDS) beyond standards and facilitates toxic metals accumulation and other problems like staining and/or precipitation.One of the treatment options for an elevated total dissolved solution is desalination using a solar driven reverse osmosis system.The northern part of Ethiopia has short rainy season and long dry weather with clear sky radiation.Solar radiation ranges from 5.46 kWh/m 2 /day in August to 6.82 kWh/m 2 /day in April, with an average of 6.09 kWh/m 2 /day.This paper deals with application of reverse osmosis, driven by desalination system using solar energy, to supply safe drinking water for the rural areas of northern Ethiopia.Reverse osmosis due to its low energy consumption is one of the best desalination alternatives.Solar powered reverse osmosis system was developed and installed at Mekelle University.The main components are photovoltaic panels, two DC powered pumps, carbon filters, and flow meters.The system made to operate in a variable power, flow, and pressure considering the naturally varying irradiance throughout the day.The entire process of irradiation potential measurements, the amount of energy generated using solar panel, and the amount of TDS is discussed.The feed water with nearly constant TDS around 2800 ppm from the study area has reduced to fairly constant TDS of about 100 ppm after desalination.The average desalination capacity of the system is 50 litres per hour. أدى التلوث والاستغلال المفرط لطبقة المياه الجوفية والمياه السطحية إلى انخفاض جودة وتوافر موارد المياه الطبيعية في العديد من المناطق. وقد أدى هذا الوضع إلى ارتفاع إجمالي المواد الصلبة الذائبة بما يتجاوز المعايير ويسهل تراكم المعادن السامة ومشاكل أخرى مثل التلطيخ و/أو هطول الأمطار. أحد خيارات المعالجة للحل المذاب الكلي المرتفع هو تحلية المياه باستخدام نظام التناضح العكسي القائم على الطاقة الشمسية. الجزء الشمالي من إثيوبيا لديه موسم أمطار قصير وطقس جاف طويل مع إشعاع السماء الصافية. يتراوح الإشعاع الشمسي من 5.46 كيلو واط ساعة/م 2 /يوم في أغسطس إلى 6.82 كيلو واط ساعة/م 2 /يوم في أبريل، بمتوسط 6.09 كيلو واط ساعة/م 2 /يوم. تتناول هذه الورقة تطبيق التناضح العكسي، مدفوعًا بنظام تحلية المياه باستخدام الطاقة الشمسية، لتوفير مياه الشرب المأمونة للمناطق الريفية في شمال إثيوبيا. يعد التناضح العكسي بسبب انخفاض استهلاكه للطاقة أحد أفضل بدائل التحلية. تم تطوير نظام التناضح العكسي الذي يعمل بالطاقة الشمسية وتركيبه في جامعة ميكيلي. المكونات الرئيسية هي الألواح الكهروضوئية، وهما يعملان بالتيار المستمر المضخات ومرشحات الكربون ومقاييس التدفق. تم تصميم النظام للعمل بقدرة وتدفق وضغط متغيرين مع الأخذ في الاعتبار الإشعاع المتغير بشكل طبيعي على مدار اليوم. تمت مناقشة العملية الكاملة لقياسات إمكانات التشعيع وكمية الطاقة المتولدة باستخدام الألواح الشمسية وكمية المواد الصلبة الذائبة. انخفضت مياه التغذية ذات المواد الصلبة الذائبة الثابتة تقريبًا حول 2800 جزء في المليون من منطقة الدراسة إلى المواد الصلبة الذائبة الثابتة إلى حد ما بحوالي 100 جزء في المليون بعد تحلية المياه. يبلغ متوسط قدرة تحلية النظام 50 لترًا في الساعة.

The wettability of a formation is defined as the tendency of one fluid to spread on a surface in competition with other fluids which are also in contact with it. However, the impact of temperature on wettability in an aquifer and the modification of relative permeability curves based on the temperature variation in aquifers is not well covered in the literature. This study redresses this dearth of information by investigating the impact of temperature on wettability distribution in a reservoir and updating the relative permeability curves based on its temperature propagation. The impact of the latter is studied in relation to the solubility of CO(2) injected into an aquifer using the numerical methods (i.e. ECLIPSE). If the CO(2) injected has a temperature higher than the formation geothermal temperature, it can change the wettability of the formation further to a more CO(2) wet condition. This increases the risk of leakage and also changes the relative permeability curves as the CO(2) moves through the reservoir, a situation that needs to be considered in reservoir simulations. The results show that updating and modifying the relative permeability curves with temperature variation in an aquifer can increase the amount of CO(2) dissolution there.

We consider the feasibility of a novel Carbon Capture, Utilization and Storage (CCUS) concept that consists in producing oil and gas from hydrocarbon-rich shales overlying deep saline aquifers that are candidates for CO2 storage. Such geological overlapping between candidate aquifers for CO2 storage and shale plays exists in several sedimentary basins across the continental US. Since CO2 reaches the storage formation at a lower temperature than the in-situ temperature, a thermal stress reduction occurs, which may lead to hydraulic fracturing of the caprock overlying the aquifer. In this work, we use a thermo-hydro-mechanical approach for modelling a caprock-aquifer-baserock system. We show that hydraulic fracturing conditions are induced within the aquifer by thermal stress reduction caused by cooling and that hydraulic fractures eventually propagate into the lower portion of the shale play. Nonetheless, fracture height of penetration in the caprock is considerably short after 10 years of injection, so the overall caprock sealing capacity is maintained. To maximize the benefit of the proposed CCUS method, CO2 injection should be maintained as long as possible to promote the penetration depth of cooling-induced hydraulic fractures into organic-rich shales. Though drilling a horizontal well in the lower portion of the shale to produce hydrocarbons from the induced hydraulic fractures may not be technically feasible, hydrocarbons can still be produced through the injection well. The production of hydrocarbons at the end of the CO2 storage project will partly compensate the costs of CCS operations. © 2017 The Authors. This study was partially supported by the Louisiana Board of Regents — Research Competitiveness Subprogram (RCS) under contract #43950. V.V. acknowledges financial support from the “TRUST" project (European Community's Seventh Framework Programme FP7/2007-2013 under grant agreement n 309607) and from “FracRisk" project (European Community's Horizon 2020 Framework Programme H2020-EU.3.3.2.3 under grant agreement n 640979). Peer reviewed

AbstractShallow aquifer monitoring is likely to be a required aspect to any geologic CO2 sequestration operation. Collecting groundwater samples and analyzing for geochemical parameters such as pH, alkalinity, total dissolved carbon, and trace metals has been suggested by a number of authors as a possible strategy to detect CO2 leakage. The effectiveness of this approach, however, will depend on the hydrodynamics of the leak-induced CO2 plume and the spatial distribution of the monitoring wells relative to the origin of the leak. To our knowledge, the expected effectiveness of groundwater sampling to detect CO2 leakage has not yet been quantitatively assessed. In this study we query hundreds of simulations developed for the National Risk Assessment Project (US DOE) to estimate risks to drinking water resources associated with CO2 leaks. The ensemble of simulations represent transient, 3-D multi-phase reactive transport of CO2 and brine leaked from a sequestration reservoir, via a leaky wellbore, into an unconfined aquifer. Key characteristics of the aquifer, including thickness, mean permeability, background hydraulic gradient, and geostatistical measures of aquifer heterogeneity, were all considered uncertain parameters. Complex temporally-varying CO2 and brine leak rate scenarios were simulated using a heuristic scheme with ten uncertain parameters. The simulations collectively predict the spatial and temporal evolution of CO2 and brine plumes over 200 years in a shallow aquifer under a wide range of leakage scenarios and aquifer characteristics.Using spatial data from an existing network of shallow drinking water wells in the Edwards Aquifer, TX, as one illustrative example, we calculated the likelihood of leakage detection by groundwater sampling. In this monitoring example, there are 128 wells available for sampling, with a density of about 2.6 wells per square kilometer. If the location of the leak is unknown a priori, a reasonable assumption in many cases, we found that the leak would be detected in at least one of the monitoring wells in less than 10% of the scenarios considered. This is because plume sizes are relatively small, and so the probability of detection decreases rapidly with distance from the leakage point. For example, 400m away from the leakage point there is less than 20% chance of detection.We then compared the effectiveness of groundwater quality sampling to shallow aquifer and/or reservoir pressure monitoring. For the Edwards Aquifer example, pressure monitoring in the same monitoring well network was found to be even less effective that groundwater quality monitoring. This is presumably due to the unconfined conditions and relatively high permeability, so pressure perturbations quickly dissipate. Although specific results may differ from site to site, this type of analysis should be useful to site operators and regulators when selecting leak detection strategies. Given the spatial characteristics of a proposed monitoring well network, probabilities of leakage detection can be rapidly calculated using this methodology.Although conditions such as these may not be favorable for leakage detection in shallow aquifers, leakage detection could be much more successful in the injection reservoir. We demonstrate proof-of-concept for this hypothesis, presenting a simulation where there is measurable pressure change at the injection well due to overpressurization, fault rupture, and consequent leakage up the fault into intermediate and shallow aquifers. The size of the detectible pressure change footprint is much larger in the reservoir than in either of the overlying aquifers. Further exploration of the range of conditions for which this technique would be successful is the topic of current study.

Abstract Design of subsurface CO2 storage sites largely relies on numeric simulation-based predictions of plume extent and progressive immobilization. In most cases, sensitivity analyses are performed with corner-point grid representations of the geo-model and first-order IFD methods using two-point flux approximation (TPFA). Here, we have conducted a comprehensive analysis of the impact of the vertical resolution of such grids on the predicted plume extent and capacity in a simplified layered aquifer system. Four different CO2 mobility and buoyancy scenarios were analyzed. To minimize grid-orientation effects, the analysis was performed for predominantly grid-axes parallel flow through regularly gridded cross-sectional models with uniform cell size and variable cell width-over-height ratios. The analysis of the role of vertical grid resolution indicates a first-order correlation between plume extent and this parameter. The results also reveal that capillary forces reduce plume extent and enhance aquifer storage for low permeability contrasts between layers. Furthermore, model sensitivity to grid resolution scales with the magnitude of the permeability contrast between layers. Inspection of these results reveals that an underestimation of CO2 mobility at the top of the plume is the root cause of the observed plume retardation. A comparison with two alternative simulators that discretize mobility as piecewise linear within cells as opposed to piecewise constant and are less resolution sensitive confirms this interpretation.

As a new “sink” of CO2 permanent storage, the depleted shale reservoir is very promising compared to the deep saline aquifer. To provide a greater understanding of the benefits of CO2 storage in a shale reservoir, a comparative study is conducted by establishing the full-mechanism model, including the hydrodynamic trapping, adsorption trapping, residual trapping, solubility trapping as well as the mineral trapping corresponding to the typical shale and deep saline aquifer parameters from the Ordos basin in China. The results show that CO2 storage in the depleted shale reservoir has merits in storage safety by trapping more CO2 in stable immobile phase due to adsorption and having gentler and ephemeral pressure perturbation responding to CO2 injection. The effect of various CO2 injection schemes, namely the high-speed continuous injection, low-speed continuous injection, huff-n-puff injection and water alternative injection, on the phase transformation of CO2 in a shale reservoir and CO2-injection-induced perturbations in formation pressure are also examined. With the aim of increasing the fraction of immobile CO2 while maintaining a safe pressure-perturbation, it is shown that an intermittent injection procedure with multiple slugs of hug-n-puff injection can be employed and within the allowable range of pressure increase, and the CO2 injection rate can be maximized to increase the CO2 storage capacity and security in shale reservoir.