Analysis of recovery efficiency in high-temperature aquifer thermal energy storage: a Rayleigh-based method

High-temperature aquifer thermal energy storage (HT-ATES) is an important technique for energy conservation. A controlling factor for the economic feasibility of HT-ATES is the recovery efficiency. Due to the effects of density-driven flow (free convection), HT-ATES systems applied in permeable aquifers typically have lower recovery efficiencies than conventional (low-temperature) ATES systems. For a reliable estimation of the recovery efficiency it is, therefore, important to take the effect of density-driven flow into account. A numerical evaluation of the prime factors influencing the recovery efficiency of HT-ATES systems is presented. Sensitivity runs evaluating the effects of aquifer properties, as well as operational variables, were performed to deduce the most important factors that control the recovery efficiency. A correlation was found between the dimensionless Rayleigh number (a measure of the relative strength of free convection) and the calculated recovery efficiencies. Based on a modified Rayleigh number, two simple analytical solutions are proposed to calculate the recovery efficiency, each one covering a different range of aquifer thicknesses. The analytical solutions accurately reproduce all numerically modeled scenarios with an average error of less than 3 %. The proposed method can be of practical use when considering or designing an HT-ATES system.     

地下含水层储能两阶段热量运移数值模型研究

为了简单而准确地预测地下含水层储能情况,考虑了地下含水层储能过程时间跨度大、储能保温分阶段的实际特点,分析了地下含水层流动和换热模型物理参数的对比特点,以热平衡和热扩散原理为基础,建立分成两个连续阶段的地下含水层储能数值计算模型.模型求解中,采用控制容积法,以全隐格式进行热扩散方程的离散化,然后应用Jacobi方法迭代求解,模拟结果和实际观测数据吻合很好.该模型还分析了含水层储能循环采灌过程中抽出储能水的温度变化的一般特点.     

深层含水层地下储热技术的发展现状与展望

深层含水层储热是一种利用深度>500 m的深层含水层作为储热介质的储热技术,储热对象通常为50~150 ℃的热水。它通过地下水井从深层含水层中抽取和灌入地下水,实现热能储存和回收。深层含水层储热技术是弥补能源供需时空分布的不平衡,综合利用多种可再生能源,实现节能减排的有效途径,是国内外研究的前沿和热点。文中首先阐述了深层含水层储热系统在世界范围内的历史发展,归纳储热系统的热工性能,在总结前人研究工作的基础上分析影响其热回收效率的关键参数,并对各个参数对热回收效率的敏感性做了综述。在此基础上,本文还讨论了限制深层含水层储热系统发展的技术瓶颈,并针对系统的经济效益和市场潜力做了预测和展望。     

Influence of geologic layering on heat transport and storage in an aquifer thermal energy storage system

A modeling study was carried out to evaluate the influence of aquifer heterogeneity, as represented by geologic layering, on heat transport and storage in an aquifer thermal energy storage (ATES) system in Agassiz, British Columbia, Canada. Two 3D heat transport models were developed and calibrated using the flow and heat transport code FEFLOW including: a “non-layered” model domain with homogeneous hydraulic and thermal properties; and, a “layered” model domain with variable hydraulic and thermal properties assigned to discrete geological units to represent aquifer heterogeneity. The base model (non-layered) shows limited sensitivity for the ranges of all thermal and hydraulic properties expected at the site; the model is most sensitive to vertical anisotropy and hydraulic gradient. Simulated and observed temperatures within the wells reflect a combination of screen placement and layering, with inconsistencies largely explained by the lateral continuity of high permeability layers represented in the model. Simulation of heat injection, storage and recovery show preferential transport along high permeability layers, resulting in longitudinal plume distortion, and overall higher short-term storage efficiencies.     

Predicting the risk of saltwater contamination of freshwater aquifers during aquifer thermal energy storage

Aquifer thermal energy storage (ATES) is an underground thermal energy storage technology with a large potential to decarbonise the heating and cooling of buildings. ATES installations typically store thermal energy in aquifers that are also exploited for potable water, so a major consideration during development is ensuring that system operation will not lead to groundwater pollution. In this study, the risk of contamination due to upconing of a shallow freshwater/saltwater interface during ATES operation is investigated. Fluid flow, and heat and salt (chloride ion) transport are simulated in a homogeneous aquifer during ATES operation via a well doublet. The impact of geological, hydrological and operational parameters is investigated in a sensitivity analysis. Two new dimensionless numbers are proposed to characterise salt upconing and redistribution during ATES operation and provide a close match to simulated concentrations: C_R,w characterises the contamination risk at the ATES installation, and C_R,d characterises the risk at locations downstream of the ATES installation with respect to background groundwater flow. ATES systems with C_R,w and C_R,d < 10 introduce low risk of contamination in a homogenous aquifer, with chloride concentration at, and downstream of, the ATES system, remaining below the World Health Organisation’s advised limit. ATES installations with C_R,w and C_R,d > 10 cause a rapid increase in aquifer chloride concentration. The results are used to estimate an exclusion distance beyond which ATES system operation will not cause contamination in a homogenous aquifer. The dimensionless parameters proposed allow rapid assessment of the potential for saltwater contamination during ATES operation.

     

B and Li isotopes as intrinsic tracers for injection tests in aquifer storage and recovery systems

Boron and Li isotopes have been tested as environmental tracers of treated sewage injected into a sandy aquifer (Shafdan reclamation project, Israel). During a 38 days injection test in a newly dug injection well, a conservative artificial tracer (Br⁻) was monitored together with δ¹¹B and δ⁷Li in the injectate, in the unsaturated soil zone (porous cup) and an observation well in the aquifer. In spite of B and Li concentrations in the injectate close to background values, significant shifts of the isotope signatures could be observed over the duration of the injection test. Boron isotope ratios show a breakthrough curve delayed with respect to Br⁻ breakthrough due to some reversible sorption on the aquifer material. No isotope fractionation was observed in the unsaturated or the saturated zone so that B isotopes can be considered as conservative in the investigated part of the aquifer system. Lithium isotopes are strongly fractionated, probably due to sorption processes. Lithium concentrations point to a Li sink in the system, δ⁷Li values vary strongly with a tendency of ⁷Li depletion in the liquid phase over the duration of the experiment. This is opposite to the expected preferential sorption of ⁶Li onto clay minerals. Boron isotopes reveals a valuable tracer of artificial recharge of freshwaters derived from treated sewage, both for short term tracer tests and for long-term monitoring of artificial recharge, even if in aquifers with higher clay contents, sorption-linked isotope fractionation cannot be excluded. More data are needed on Li isotope fractionation in natural groundwater systems to assess the potential of this tracer as monitoring tool.     

Effects of thermal energy storage on shallow aerobic aquifer systems: temporary increase in abundance and activity of sulfate-reducing and sulfur-oxidizing bacteria

Aquifer thermal energy storage may result in increases in the groundwater temperature up to 70 °C and more. This may lead to geochemical and microbiological alterations in the aquifer. To study the temperature effects on the indigenous microbial community composition, sediment column experiments at four different temperatures were carried out and the effluents were characterized geochemically and microbiologically. After an equilibrium phase at groundwater temperature of 10 °C for 136 days, one column was kept at 10 °C as a reference and the others were heated to 25, 40 and 70 °C. Genetic fingerprinting and quantitative PCR revealed a change in the bacterial community composition and abundance due to the temperature increase. While at 25 °C only slight changes in geochemical composition and gene copy numbers for bacteria were observed, increasing concentrations of total organic carbon in the 40 °C column were followed by a strong increase in bacterial abundance. Thermophilic bacteria became dominant at 70 °C. Temporary sulfate reduction took place at 40 and 70 °C and this correlated with an increased abundance of sulfate-reducing bacteria (SRB). Furthermore, a coexistence of SRB and sulfur-oxidizing bacteria (SOB) at all temperatures indicated an interaction of these physiological groups in the sediments. The results show that increased temperatures led to significant shifts in the microbial community composition due to the altered availability of electron donors and acceptors. The interplay of SRB and SOB in sedimentary biofilms facilitated closed sulfur cycling and diminished harmful sulfur species.     

Effects of regional groundwater flow on the performance of an aquifer thermal energy storage system under continuous operation

Numerical investigations and a thermohydraulic evaluation are presented for two-well models of an aquifer thermal energy storage (ATES) system operating under a continuous flow regime. A three-dimensional numerical model for groundwater flow and heat transport is used to analyze the thermal energy storage in the aquifer. This study emphasizes the influence of regional groundwater flow on the heat transfer and storage of the system under various operation scenarios. For different parameters of the system, performances were compared in terms of the temperature of recovered water and the temperature field in the aquifer. The calculated temperature at the producing well varies within a certain range throughout the year, reflecting the seasonal (quarterly) temperature variation of the injected water. The pressure gradient across the system, which determines the direction and velocity of regional groundwater flow, has a substantial influence on the convective heat transport and performance of aquifer thermal storage. Injection/production rate and geometrical size of the aquifer used in the model also impact the predicted temperature distribution at each stage and the recovery water temperature. The hydrogeological-thermal simulation is shown to play an integral part in the prediction of performance of processes as complicated as those in ATES systems.     

Radial Dupuit interface flow to assess the aquifer storage and recovery potential of saltwater aquifers

A new accurate numerical solution is presented for aquifer storage and recovery (ASR) systems in coastal aquifers; flow is approximated as radial Dupuit interface flow. The radial velocities of points on the interface are a function of time, the vertical coordinate, and the dimensionless parameter D (the discharge of the well divided by the product of the hydraulic conductivity, the square of the aquifer thickness, and the dimensionless density difference). The recovery efficiency of an ASR system (the ratio of the recovered volume of water divided by the injected volume of water) is determined by D and by the relative lengths of the injection, storage and recovery periods. Graphs are produced for the recovery efficiency as a function of parameter D for ASR operations with and without storage periods and for multiple cycles. The presented solutions and graphs are to be used as screening tools to assess the feasibility of specific injection, storage and recovery scenarios of planned ASR systems in saltwater aquifers without having to run complicated flow and transport models. When the screening tool indicates that recovery efficiencies are acceptable, the consideration of other features such as mixing and chemistry is warranted.     

正确使用泥浆,提高水文地质钻探效率

本文介绍了泥浆在水文地质钻探中的作用,在各种地层中如何正确使用泥浆,以减少孔内事故,提高钻进效率,提高我们的水文水井钻探技术。     

Experimental and simulation study on the impact of storage and recovery of coastal aquifer to seawater intrusion

Natural Hazards - The horizontal seismic responses in cold regions have not received adequate attentions. In seismic design for frozen ground, computations for unfrozen ground are generally adopted...     

Identification of potential sites for aquifer storage and recovery (ASR) in coastal areas using ASR performance estimation methods

Performance of freshwater aquifer storage and recovery (ASR) systems in brackish or saline aquifers is negatively affected by lateral flow, density effects, and/or dispersive mixing, causing ambient groundwater to enter ASR wells during recovery. Two recently published ASR performance estimation methods are applied in a Dutch coastal area, characterized by brackish-to-saline groundwater and locally high lateral-flow velocities. ASR performance of existing systems in the study area show good agreement with the predicted performance using the two methods, provided that local vertical anisotropy ratios are limited (<3). Deviations between actual and predicted ASR performance may originate from simplifications in the conceptual model and uncertainties in the hydrogeological and hydrochemical input. As the estimation methods prove suitable to predict ASR performance, feasibility maps are generated for different scales of ASR to identify favorable ASR sites. Successful small-to-medium-scale ASR varies spatially in the study area, emphasizing the relevance of reliable a priori spatial mapping.     

The origin of increased salinity in the Cambrian-Vendian aquifer system on the Kopli Peninsula,northern Estonia

Monitoring of the confined Cambrian-Vendian aquifer system utilised for industrial water supply at Kopli Peninsula in Tallinn over 24 years reveals remarkable changes in chemical composition of groundwater. A relatively fast 1.5 to 3.0-fold increase in TDS and in concentrations of major ions in abstracted groundwater is the consequence of heavy pumping. The main sources of dissolved load in Cambrian-Vendian groundwater are the leaching of host rock and the other geochemical processes that occur in the saturated zone. Underlying crystalline basement, which comprises saline groundwater in its upper weathered and fissured portion, and which is hydraulically connected with the overlying Cambrian-Vendian aquifer system, is the second important source of ions. The fractured basement and its clayey weathering crust host the Ca-Cl type groundwater, which is characterised by high TDS values (2–20 g/L). Intensive water abstraction accelerates the exchange of groundwaters and increases the area of influence of pumping. Chemical and isotopic studies of groundwater indicate an increasing contribution of old brackish water from the crystalline basement and rule out the potential implication of an intrusion of seawater into aquifer.

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Resumen El origen del incremento en salinidad en un sistema de acuíferos Cámbrico-Vendiano en la Península Kopli, norte de EstonieMonitoreo a largo plazo de un sistema de acuíferos confinados, de edad Cámbrico-Vendiano, que se utiliza como fuente de abastecimiento industrial en la Península Kopli, al norte de Estonie, revela cambios notables en la composición química del agua subterránea. Un incremento de 1.5 a 3 veces en TDS y en concentraciones de iones mayores en agua subterránea explotada ha sido ocasionado por bombeo fuerte. Las fuentes principales de carga disuelta en el agua subterránea Cámbrico-Vendiano son la lixiviación de la roca encajonante y los procesos geoquímicos que ocurren en la zona saturada. Basamento cristalino subyacente, que aloja agua subterránea salada en la parte superior intemperizada y fisurada, y está conectado hidráulicamente con el sistema acuífero Cámbrico-Vendiano sobreyacente, es la segunda fuente importante de iones. El basamento fracturado y su corteza de intemperismo arcillosa alojan agua subterránea de tipo Ca-Cl la cual se caracteriza por valores altos de TDS (2–20 g/l). Debido a extracción intensiva se ha acelerado el intercambio de agua subterránea y se ha incrementado el área de influencia del bombeo. Los estudios químicos e isotópicos de agua subterránea indican una contribución creciente por filtración derivada del basamento cristalino. Es evidente una intrusión de agua salada hacia el sistema de acuíferos con implicaciones subsecuentes para la calidad del agua.

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Résumé Lorigine de la salinité croissante dans le système aquifère du Cambrien-Vendien dans la péninsule de Kopli, nord de lEstonieLe suivi à long terme du système aquifère captif du Cambrien-Vendien utilisé pour lapprovisionnement deaux industrielles dans la Péninsule de Kopli, nord de lEstonie, révèle de remarquables changements dans la composition chimique des eaux souterraines. Une augmentation de facteur 1.5 à 3 de la TDS et des concentrations en ions majeurs dans leau souterraine est la conséquence de pompages intensifs. Les sources principales des charges dissoutes dans les eaux de laquifère du Cambrien-Vendien sont le lessivage des roches et dautres phénomènes géochimiques ayant lieu dans la zone saturée. Le soubassement rocheux cristallin, qui renferme des eaux souterraines salines dans sa partie supérieure altérée et fissurée, et est hydrauliquement connecté avec laquifère supérieur du Cambrien-Vendien, est la deuxième importante source dions. Le soubassement fracturé et le matériel argileux de laltération, renferme leau souterraine de type Ca-Cl, caractérisée par un haut TDS (2–20 g/l). A cause de la mobilisation intensive de leau les échanges deau souterraine est sont accélérés et la zone dinfluence des pompages augmentent. Les études chimiques et isotopiques indiquent une contribution croissante du drainage des eaux du soubassement cristallin. Lintrusion deaux salées de la mer dans le système aquifère nest pas un phénomène évident.

     

Impact of drilling mud on chemistry and microbiology of an Upper Triassic groundwater after drilling and testing an exploration well for aquifer thermal energy storage in Berlin (Germany)

After completion of an exploration well, sandstones of the Exter Formation were hydraulically tested to determine the hydraulic properties and to evaluate chemical and microbial processes caused by drilling and water production. The aim was to determine the suitability of the formation as a reservoir for aquifer thermal energy storage. The tests revealed a hydraulic conductivity of 1–2 E-5 m/s of the reservoir, resulting in a productivity index of 0.6–1 m³/h/bar. A hydraulic connection of the Exter Formation to the overlaying, artesian “Rupelbasissand” cannot be excluded. Water samples were collected for chemical and microbiological analyses. The water was similarly composed as sea water with a maximum salinity of 24.9 g/L, dominated by NaCl (15.6 g/L Cl and 7.8 g/L Na). Until the end of the tests, the water was affected by drilling mud as indicated by the high pH (8.9) and high bicarbonate concentration (359 mg/L) that both resulted from the impact of sodium carbonate (Na₂CO₃) additives. The high amount of dissolved organic matter (>?58 mg/L) and its molecular-weight distribution pattern indicated that residues of cellulose, an ingredient of the drilling mud, were still present at the end of the tests. Clear evidence of this contamination gave the measured uranine that was added as a tracer into the drilling mud. During fluid production, the microbial community structure and abundance changed and correlated with the content of drilling mud. Eight taxa of sulfate-reducing bacteria, key organisms in processes like bio-corrosion and bio-clogging, were identified. It can be assumed that their activity will be affected during usage of the reservoir.