No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Preface: Hydrogeology of shallow thermal systems
Abstract
IntroductionHydrogeology plays an important role in the transfer of heat in geological systems. Large-scale variations in the permeability distribution (including the presence of fracture zones and faults) can significantly impact the coupled flow of heat and fluid (Smith and Chapman 1983). At the regional scale, groundwater flow can alter the heat distribution, depressing or enhancing thermal gradients in space and time, and carry heat over significant distances (Smith and Chapman 1983; Woodbury and Smith 1985; Molina-Giraldo et al. 2011). At smaller scales, groundwater flow can present challenges to the proper design of geo-exchange systems and can limit the success of aquifer thermal energy storage (ATES) and borehole thermal energy storage (BTES) systems (e.g. Sauty et al. 1982a, b).This special issue of Hydrogeology Journal presents a collection of articles that aim to advance understanding of coupled hydrogeological and thermal processes over a range of spatial and temporal scale ...
... Other studies relate to the simulation of relatively short durations of system use or short duration (injection) experiments (Papadopulos and Larson 1978;Tsang et al. 1981;Buscheck et al. 1983;Dwyer and Eckstein 1987;Xue et al. 1990;Palmer et al. 1992;Molson et al. 1992;Vandenbohede et al. 2009Vandenbohede et al. , 2011. Allen et al. (2014) recognize aquifer heterogeneity as a critical aspect for understanding coupled flow and heat transport. Bridger and Allen (2010), (2014) and Sommer et al. (2014) investigated the role of heterogeneous hydraulic and thermal properties of the aquifer in the development of the thermal anomalies. ...
Results are presented of a comprehensive thermal impact study on an aquifer thermal energy storage (ATES) system in Bilthoven, the Netherlands. The study involved monitoring of the thermal impact and modeling of the three-dimensional temperature evolution of the storage aquifer and over-and underlying units. Special attention was paid to non-uniformity of the background temperature, which varies laterally and vertically in the aquifer. Two models were applied with different levels of detail regarding initial conditions and heterogeneity of hydraulic and thermal properties: a fine-scale hetero-geneity model which construed the lateral and vertical temperature distribution more realistically, and a simplified model which represented the aquifer system with only a limited number of homogeneous layers. Fine-scale heterogeneity was shown to be important to accurately model the ATES-impacted vertical temperature distribution and the maximum and minimum temperatures in the storage aquifer, and the spatial extent of the thermal plumes. The fine-scale hetero-geneity model resulted in larger thermally impacted areas and larger temperature anomalies than the simplified model. The models showed that scattered and scarce monitoring data of ATES-induced temperatures can be interpreted in a useful way by groundwater and heat transport modeling, resulting in a realistic assessment of the thermal impact.
... Deeply buried carbonate units in foreland basinal settings overlain by thick successions of siliciclastic sediments are prospective sites for hydrocarbon and geothermal exploration (Goldscheider et al., 2010). However, the exploration of these deep areas is expensive, and is further complicated by tectonic conditions which make seismic data acquisition difficult, as well as resulting in highly heterogeneous reservoir quality (Allen et al., 2014). In addition, the hydraulic conditions occurring in confined carbonate units are difficult to characterize due to the general lack of data. ...
This study examines the patterns of groundwater flow and salinity in a region of confined basement carbonate aquifer along with the region's unconfined adjacent part and siliciclastic confining strata. An understanding of regional-scale flow patterns in this setting may prompt a rethinking of the traditional view. According to that view confined carbonates are bounded and isolated by impermeable confining layers from their surroundings. A basin-scale analysis of the subsurface conditions promises better to accentuate otherwise unseen signs of hydraulic communication both horizontally and vertically between different parts of the flow domain. This study reveals that various flow regimes exist, in the area of the Paleogene Basin, Hungary. The pattern and intensity of these flow regimes depend on the elevation of basement carbonates and the structures, thickness, hydraulic conductivity and heterogeneity of the covering layers. Effects of gravity-driven regional groundwater flow were identified down to an elevation of −500 m asl including recharge and discharge areas. Hydraulic communication occurs both vertically and laterally in this zone but the direction and intensity of flow are influenced by aquitards or confining layers. Nevertheless, a hydraulic boundaries (a colinear ridge in the north and a sink in the south) was recognized in the study area. This impedes horizontal hydraulic communication between the shallower unconfined-to confined carbonates in the west and the deeper confined carbonates in the east. Southeasterly through-flow can be observed below −500 m asl elevation which terminates in a regionally underpressured zone due to a regional aquitard in the zone of uplift. Both underpressured and overpressured blocks bounded by faults appear to influence vertical connections between siliciclastic confining layers and carbonates in the vicinity of significant strike-slip faults. The flow regimes thus recognized affect the subsurface salinity pattern, and hydrocarbon migration and as a result the planning of geothermal exploration. Consequently, a priori assumption of impermeability of confining layers and hydraulically isolated carbonate compartments below seems to be an oversimplification.
... Sedimentary basins, siliciclastic and carbonate, are targets for the installation of geothermal power plans and for direct-use of thermal water depending on their temperature conditions (Goldscheider et al., 2010). It can be seen that the hydrogeological aspects of geothermal energy utilization has got to the focus of interest nowadays (Allen et al., 2014). However, our knowledge regarding geothermal resources in the context of basin scale operating hydrodynamic systems is restricted (Tóth, 1995). ...
The paper proposes the involvement of preliminary regional hydrodynamic analysis for the reconnaisance phase water-based geothermal exploration in sedimentary basins. This approach is based on basin-scale pore pressure evaluation, it complements the usual reservoir and temperature analyses. Understanding of subsurface pore pressure distribution is beneficial not only in planning thermal water production but also in reinjection. The method is demonstrated for a sedimentary basin characterized by overpressured and superimposed gravity-driven flow. The key point of the approach is the understanding of regional pressure regimes and the delineation of the boundary of overpressured and gravitational flow domains.
Natural springs have the potential to provide important information on hydrogeochemical processes within aquifers. This study used traditional and classic technical methods and procedures to determine the characteristics and evolution of springs to gain further knowledge on the differences between hot saline springs and cold fresh springs. In a short river segment near Wenquanzhen in the eastern Sichuan Basin, southwest China, several natural springs coexist with total dissolved solids (TDS) ranging from less than 1 to 15 g/L and temperatures from 15 to 40 °C. The springs emanate from the outcropping Lower and Middle Triassic carbonates in the river valley cutting the core of an anticline. The cold springs are of Cl·HCO3-Na·Ca and Cl·SO4-Na types, and the hot saline springs are mainly of Cl-Na type. The chemistry of the springs has undergone some changes with time. The stable hydrogen and oxygen isotopes indicate that the spring waters are of a meteoric origin. The salinity of the springs originates from dissolution of minerals, including halite, gypsum, calcite and dolomite. The evolution of the springs involves the following mechanisms: the groundwater receives recharge from infiltration of precipitation, then undergoes deep circulation in the core of the anticline (incongruent dissolution of the salt-bearing strata occurs), and emerges in the river valley in the form of hot springs with high TDS. Groundwater also undergoes shallow circulation in the northern and southern flanks of the anticline and appears in the river valley in the form of cold springs with low TDS.
This contribution studies the usability of aquifer thermal energy storage (ATES) for seasonal solar heat storage by means of thermo-hydraulic modeling. The geological setting refers to the Northeast German Basin (NEGB), specifically a site ca. 50 km west of Berlin, Germany. The considered storage formation is located in Jurassic sandstones at about 270 m depth below surface, showing an in-situ (undisturbed) formation temperature of around 17 °C and appropriate hydraulic storage properties. The paper considers idealised doublet systems in faulted as well as unfaulted reservoir domains and study the energy- and mass transport of simulated ATES systems. Five perennial loading/unloading series of solar thermal energy are inestigated, assumed to be harvested by a hectare-sized flat plate collector field, which is modeled employing climate data of the considered region. The simulation results exemplarily show how the storage system develops temperature-conserving recovery fractions of up to 80% heat recovery during the first years of operation.
Mixing is a dominant hydrogeological process in the hydrothermal spring system in the Cappadocia region of Turkey. All springs emerge along faults, which have the potential to transmit waters rapidly from great depths. However, mixing with shallow meteoric waters within the flow system results in uncertainty in the interpretation of geochemical results. The chemical compositions of cold and warm springs and geothermal waters are varied, but overall there is a trend from Ca–HCO3 dominated to Na–Cl dominated. There is little difference in the seasonal ionic compositions of the hot springs, suggesting the waters are sourced from a well-mixed reservoir. Based on δ18O and δ2H concentrations, all waters are of meteoric origin with evidence of temperature equilibration with carbonate rocks and evaporation. Seasonal isotopic variability indicates that only a small proportion of late spring and summer precipitation forms recharge and that fresh meteoric waters move rapidly into the flow system and mix with thermal waters at depth. 3H and percent modern carbon (pmC) values reflect progressively longer groundwater pathways from cold to geothermal waters; however, mixing processes and the very high dissolved inorganic carbon (DIC) of the water samples preclude the use of either isotope to gain any insight on actual groundwater ages.
We present an overview of the risks that underground thermal energy storage (UTES) can impose on the groundwater system, drinking water production, and the subsurface environment in general. We describe existing policy and licensing arrangements for UTES in the Netherlands, as well as the capability of the current and future Dutch policy and legal framework to minimize or mitigate risks from UTES on groundwater resources. A survey at the European Union member state level indicates that regulation and research on the potential impacts of UTES on groundwater resources and the subsurface environment often lag behind the technological development of and ever-growing demand for this renewable energy source. The lack of a clear and scientifically underpinned risk management strategy implies that potentially unwanted risks might be taken at vulnerable locations such as near well fields used for drinking water production, whereas at other sites, the application of UTES is avoided without proper reasons. This means that the sustainability of UTES as a form of renewable energy is currently not fully understood, and the technology may be compromising the natural resilience of the subsurface environment. We recognize three main issues that should be addressed to secure sustainable application of UTES: Scientific research is required to further elucidate the impacts of UTES on groundwater; cross-sectoral subsurface planning is required to minimize negative conflicts between UTES and other subsurface interests; and EU-wide guidelines and standards are required for quality assurance and control when installing UTES systems.
A comprehensive overview of potential environmental effects during the life cycle of geothermal power plants is presented using widely scattered available information from diverse literature sources. It is shown that so far only few studies provide quantitative estimates on both direct and indirect environmental consequences. Life cycle assessment (LCA) studies on geothermal electricity production are scarce and typically country- or site-specific with a focus on the geothermal fields in the western USA. In fact a general assessment is challenging due to the dissimilar nature and maturity of currently applied geothermal power plants, the influence of site-specific characteristics, and uncertainty in long-term productivity. Especially life cycle fugitive emissions, the thread from geological hazards, and water and land use effects are highly variable and may even change with time. Based on our survey, ranges are provided for emissions and resource uses of current worldwide geothermal power generation. We also define an approximate universal case that represents an expected average. The collected data is suitable to feed life cycle inventories, but is still incomplete. Potential emissions of critical toxic substances such as mercury, boron and arsenic and their local and regional environmental consequences are particularly inadequately addressed on the global scale.
Aquifers used for the production of drinking water are increasingly being used for the generation of shallow geothermal energy. This causes temperature perturbations far beyond the natural variations in aquifers and the effects of these temperature variations on groundwater quality, in particular trace elements, have not been investigated. Here, we report the results of column experiments to assess the impacts of temperature variations (5°C, 11°C, 25°C and 60°C) on groundwater quality in anoxic reactive unconsolidated sandy sediments derived from an aquifer system widely used for drinking water production in the Netherlands. Our results showed that at 5 °C no effects on water quality were observed compared to the reference of 11°C (in situ temperature). At 25°C, As concentrations were significantly increased and at 60 °C, significant increases were observed pH and DOC, P, K, Si, As, Mo, V, B, and F concentrations. These elements should therefore be considered for water quality monitoring programs of shallow geothermal energy projects. No consistent temperature effects were observed on Na, Ca, Mg, Sr, Fe, Mn, Al, Ba, Co, Cu, Ni, Pb, Zn, Eu, Ho, Sb, Sc, Yb, Ga, La, and Th concentrations, all of which were present in the sediment. The temperature-induced chemical effects were probably caused by (incongruent) dissolution of silicate minerals (K and Si), desorption from, and potentially reductive dissolution of, iron oxides (As, B, Mo, V, and possibly P and DOC), and mineralisation of sedimentary organic matter (DOC and P).
A brief discussion and review of the geothermal reservoir systems, geothermal energy and modeling and simulation of the geothermal reservoirs has been presented here. Different types of geothermal reservoirs and their governing equations have been discussed first. The conceptual and numerical modeling along with the representation of flow though fractured media, some issues related to non isothermal flow through fractured media, the efficiency of the geothermal reservoir, structure of the numerical models, boundary conditions and calibration procedures have been illustrated. A brief picture of the Indian scenario and some barriers related with geothermal power are discussed and presented thereafter. Finally some gaps of the existing knowledge and recent focuses of research are discussed.
The objective of the current study was to assess the technical and economic factors that influence the design and performance of vertical GSHP (ground source heat pump) systems and to evaluate the spatial correlation that these factors have with geographic components such as geology and climatic conditions. The data from more than 1100 individual GSHP systems were analysed. The average capital cost of one GSHP system is about 23,500 € ± 6800 €; the large standard deviation is primarily caused by local market dynamics. In comparison to other countries such as USA, Austria, Norway, UK and Sweden, the highest capital costs for vertical GSHP systems are in Germany and Switzerland, which is almost certainly partly due to economies of scale. Although geological, hydrogeological and thermal conditions in the studied state considerably vary spatially and the evaluated specific heat extraction rates are heterogeneously distributed, no correlation between the subsurface characteristics and the design of GSHP systems could be identified. This outcome suggests that as yet subsurface characteristics are not adequately considered during the planning and design of small-scale GSHP systems, which causes an under- or oversizing and therefore a long-term impact on the maintenance costs and payback time of such systems.Highlights► The average capital cost of one GSHP system in Germany is about 23,500 € ± 6800 €. ► 51% of the capital costs are for drilling the BHE (borehole heat exchanger). ► Capital costs in Germany are very high in comparison to other countries. ► Site-specific conditions have no impact on the observed capital costs.
While research focuses mainly on the intensively used shallower aquifers, only a little research has addressed groundwater movement in deeper aquifers. This is mainly because of the negligible relevance of deep groundwater for daily usage and the great efforts and high costs associated with its access. In the last few decades, the discussion about deep geological final repositories for radioactive waste has generated strong demand for the investigation and characterization of deep-lying aquifers. Other utilizations of the deeper underground have been added to the discussion: the use of geothermal energy, potential CO2 storage, and sources of potable water as an alternative to the geogenic or anthropogenic contaminated shallow aquifers. As a consequence, the fast growing requirement for knowledge and
understanding of these dynamic systems has spurred the research on deep groundwater systems and accordingly the development of suitable test methods, which currently show considerable limitations. This review provides an overview of the history of deep groundwater research. Deep groundwater flow and research in the main hydrogeological units is presented based on six projects and the methods used. The
study focuses on Germany and two other locations in Europe.
A review of coupled groundwater and heat transfer theory is followed by an introduction to geothermal measurement techniques. Thereafter, temperature-depth profiles (geotherms) and heat discharge at springs to infer hydraulic parameters and processes are discussed. Several studies included in this review state that minimum permeabilities of approximately 5 × 10−17 < k
min <10−15 m2 are required to observe advective heat transfer and resultant geotherm perturbations. Permeabilities below k
min tend to cause heat-conduction-dominated systems, precluding inversion of temperature fields for groundwater flow patterns and constraint of permeabilities other than being <k
min. Values of k
min depend on the flow-domain aspect-ratio, faults and other heterogeneities, anisotropy of hydraulic and thermal parameters, heat-flow rates, and the water-table shape. However, the k
min range is narrow and located toward the lower third of geologic materials, which exhibit permeabilities of 10−21 < k < 10−7 m2. Therefore, a wide range of permeabilities can be investigated by analyzing subsurface temperatures or heat discharge at springs. Furthermore, temperature is easy and economical to measure and because thermal material properties vary far less than hydraulic properties, temperature measurements tend to provide better-constrained groundwater flow and permeability estimates. Aside from hydrogeologic insights, constraint of advective/conductive heat transfer can also provide information on magmatic intrusions, metamorphism, ore deposits, climate variability, and geothermal energy.
The current knowledge on thermal water resources in carbonate rock aquifers is presented in this review, which also discusses geochemical processes that create reservoir porosity and different types of utilisations of these resources such as thermal baths, geothermal energy and carbon dioxide (CO(2)) sequestration. Carbonate aquifers probably constitute the most important thermal water resources outside of volcanic areas. Several processes contribute to the creation of porosity, summarised under the term hypogenic (or hypogene) speleogenesis, including retrograde calcite solubility, mixing corrosion induced by cross-formational flow, and dissolution by geogenic acids from deep sources. Thermal and mineral waters from karst aquifers supply spas all over the world such as the famous bath in Budapest, Hungary. Geothermal installations use these resources for electricity production, district heating or other purposes, with low CO(2) emissions and land consumption, e.g. Germany's largest geothermal power plant at Unterhaching near Munich. Regional fault and fracture zones are often the most productive zones, but are sometimes difficult to locate, resulting in a relatively high exploration uncertainty. Geothermal installations in deep carbonate rocks could also be used for CO(2) sequestration (carbonate dissolution would partly neutralise this gas and increase reservoir porosity). The use of geothermal installations to this end should be further investigated.
According to the decision of the German Parliament, forward-looking, environmentally responsible, and examplary energetic concepts were to be implemented for the supply of energy to the Parliament buildings in the Spree river curve in Berlin, focusing on the high utilisation of the primary energy. Vegetable-oil fired block type cogeneration units and the integration of one aquifer heat and cold store, respectively, are to make sure that 82 % of the electric work of the overall complex and even 90 % of the annual heat demand will be covered by power and heat cogeneration. The cold store – to be charged in particular with ambient winter cold – will cover 60 % of the cold demand in summer. Thus, the environment-benign combustion of bio-fuel plus the operation of the cold store will result in a 60 % reduction of CO 2 emission compared to conventional technical solutions. At the time of the compilation of this manuscript, the system was in the phase of commissioning.
The thermal use of the shallow subsurface is increasingly being promoted and implemented as one of many promising measures for saving energy. A series of questions arises concerning the design and management of underground and groundwater heat extraction systems, such as the sharing of the thermal resource and the assessment of its long-term potential. For the proper design of thermal systems it is necessary to assess their impact on underground and groundwater temperatures.
Thermal Use of Shallow Groundwater introduces the theoretical fundamentals of heat transport in groundwater systems, and discusses the essential thermal properties. It presents a complete overview of analytical and numerical subsurface heat transport modeling, providing a series of mathematical tools and simulation models based on analytical and numerical solutions of the heat transport equation. It is illustrated with case studies from Austria, Germany, and Switzerland of urban thermal energy use, and heat storage and cooling.
This book gives a complete set of analytical solutions together with MATLAB® computer codes ready for immediate application or design. It offers a comprehensive overview of the state of the art of analytical and numerical subsurface heat transport modeling for students in civil or environmental engineering, engineering geology, and hydrogeology, and also serves as a reference for industry professionals.
This paper presents the results of a theoretical study on the thermal behavior of a hot water storage system in an aquifer using a single well. It is shown that the storage efficiency and temperature are controlled by a limited number of dimensionless groups that depend on the aquifer's physical characteristics and the storage operating parameters. A numerical model is checked against analytical solutions and then is used to evaluate the variation with time of the well temperature during production periods for symmetrical cycles (production volume and flowrate equal to injection volume and flowrate). 14 refs.
Ten successive in situ experimental investigations of hot water storage by a single well and a pair of wells (doublet) were conducted in 1976-1977 at Bonnaud, Jura, in a confined aquifer 2.5 m thick. The injected volumes ranged from 500-1700 m3. Temperature profiles were measure daily in 12 boreholes distributed along two perpendicular axes within 13 m of the injection well. Individual temperatures were measured by ten thermistors placed in the caprock. The results are discussed and used to calibrate two mathematical models. An axisymmetric model allows the calibration of average values of the parameters, while a three-dimensional model is used to determine their spatial variation in the horizontal plane. The latter model leads to the identification of a nonhomogeneous transmissibility field which fully accounts for both hydraulic and thermal contour curves. The models, which were matched against particular experiments, proved accurate when simulating other periods. Evidence is given of the importance to the recovery ratio of thermal dispersion in the aquifer and of the water content of the caprock. In a final section, experimental results of single well storage at Bonnaud, Campuget, and Auburn are compared with general type curves derived in the companion paper. They prove to yield adequate predictions of water temperature during the production phases.
Numerical solutions of the coupled equations of fluid flow and heat transport are used to investigate how the near-surface thermal regime is perturbed by groundwater flow in a basin with a three-dimensional water table configuration. We consider specifically those conditions where the hydraulic gradient on the water table drives the flow system, thermally induced buoyancy forces modify but do not control the flow field. The hydrologic disturbance of the thermal field and the significance of a water table gradient transverse to the regional slope depend upon the interplay of the three-dimensional water table configuration, the basin geometry including the depth to the basal impermeable boundary, the anisotropy, and the permeability of the subsurface formations. These factors act together to determine groundwater flow patterns, depths of circulation along individual flow lines, and areal distribution of groundwater recharge and discharge. The uniformity of surface heat flow values determined from a series of shallow boreholes in an advectively disturbed regime will depend on the location of the measurement sites relative to the hinge line separating areas of groundwater recharge and discharge and on the extent of the region centered about the hinge line where fluid inflow/outflow rates are insufficient to perturb the thermal field.
Numerical solutions of the equations of fluid flow and heat transport are used to quantify the effects of groundwater flow on the subsurface thermal regime. Simulations are carried out for a vertical section through a basin with a distance of 40 km separating the regional topographic high and low. Emphasis is placed on understanding the conditions under which advective effects significantly perturb the thermal field. The transition from conduction-dominated to advection-dominated thermal regimes is sharp and depends primarily on the topographic configuration of the water table, the magnitude and spatial distribution of permeability, hydraulic anisotropy, and the depth of active flow. Deviations of surface heat flow from the background heat flux are a measurable effect of groundwater flow and depend on the same factors. Our results show that from 0% to almost 100% of the section may have surface heat flow significantly different from background heat flow, depending upon the nature of the hydrogeologic environment. A limited spatial variability in a distributed set of heat flow measurements and/or linear temperature-depth profiles does not ensure that surface heat flow measurements are not disturbed. The results of our simulations suggest that knowledge of the complete environment of a site, including the water table configuration and subsurface flow system, combined with more closely spaced heat flow measurements may be necessary to unravel the true background heat flux in active flow regions.
This authoritative guide provides a basis for understanding the emerging technology of ground source heat pumps. It equips engineers, architects, planners, regulators and geologists with the fundamental skills needed to manipulate the ground’s huge capacity to store, supply and receive heat, and to implement technologies (such as heat pumps) to exploit that capacity for space heating and cooling.
The author has geared the book towards understanding ground source heating and cooling from the ground side (the geological aspects), rather than solely the building aspects.
An Introduction to Thermogeology: Ground Source Heating & Cooling explains the science behind thermogeology and offers practical guidance on different design options.
The science of ‘thermogeology’ can be defined as the study of the storage and transfer of low-enthalpy heat in the relatively shallow geological environment. It is characterized by numerous analogies with groundwater flow theory; indeed, modern hydrogeology has roots in heat flow theory. Heat conduction is governed by Fourier's Law and is directly analogous to Darcy's (groundwater) Law. Groundwater head, hydraulic conductivity and storage have thermogeological analogues in temperature, thermal conductivity and volumetric heat capacity. Advection of heat with groundwater flow is directly analogous to the advective transport of a reversibly sorbed, retarded contaminant.
In many regions of the world, flooded mines are a potentially cost-effective option for heating and cooling using geothermal
heat pump systems. For example, a single coal seam in Pennsylvania, West Virginia, and Ohio contains 5.1 x 1012 L of water. The growing volume of water discharging from this one coal seam totals 380,000 L/min, which could theoretically
heat and cool 20,000 homes. Using the water stored in the mines would conservatively extend this option to an order of magnitude
more sites. Based on current energy prices, geothermal heat pump systems using mine water could reduce annual costs for heating
by 67% and cooling by 50% over conventional methods (natural gas or heating oil and standard air conditioning).
The worldwide experience of reinjection in geothermal fields is reviewed. Information from 91 electric-power producing geothermal fields shows that: a reinjection plan should be developed as early as possible in field development and it should be flexible as it is likely to change with time. The optimum reinjection strategy depends on the type of geothermal system. For vapour-dominated systems which can run out of water reinjection should be infield. While for hot water and liquid-dominated two-phase systems (low-enthalpy and medium-enthalpy) reinjection is likely to involve a mix of infield and outfield injection. In general infield reinjection provides pressure support and thus reduces drawdown and the potential for subsidence, whereas outfield reinjection reduces the risk of cold water returning to the production area. Deep reinjection reduces the risk of groundwater contamination and ground surface inflation. The proportion of infield to outfield reinjection and the location (deep or shallow) is case specific and typically the infield reinjection rate will vary with time as part of the steam field management strategy.
An overview on the geothermal energy technology and current status is presented. The earth's heat flow, geothermal gradient, types of geothermal fields, the geologic environment of geothermal energy and the methods of exploration for geothermal resources including drilling and resource assessment are defined. The geothermal electrical installed capacity in the world is 7974 MW and the electrical energy generated is 49.3 billion, kWh/year which represents 0.3 % of the world total electrical energy.
Geothermal Heat Pumps, or Ground Coupled Heat Pumps (GCHP), are systems combining a heat pump with a ground heat exchanger (closed loop systems), or fed by ground water from a well (open loop systems). They use the earth as a heat source when operating in heating mode, with a fluid (usually water or a water–antifreeze mixture) as the medium that transfers the heat from the earth to the evaporator of the heat pump, thus utilising geothermal energy. In cooling mode, they use the earth as a heat sink. With Borehole Heat Exchangers (BHE), geothermal heat pumps can offer both heating and cooling at virtually any location, with great flexibility to meet any demands. More than 20 years of R&D focusing on BHE in Europe has resulted in a well-established concept of sustainability for this technology, as well as sound design and installation criteria. Recent developments are the Thermal Response Test, which allows in-situ-determination of ground thermal properties for design purposes, and thermally enhanced grouting materials to reduce borehole thermal resistance. For cooling purposes, but also for the storage of solar or waste heat, the concept of underground thermal energy storage (UTES) could prove successful. Systems can be either open (aquifer storage) or can use BHE (borehole storage). Whereas cold storage is already established on the market, heat storage, and, in particular, high temperature heat storage (> 50 °C) is still in the demonstration phase. Despite the fact that geothermal heat pumps have been in use for over 50 years now (the first were in the USA), market penetration of this technology is still in its infancy, with fossil fuels dominating the space heating market and air-to-air heat pumps that of space cooling. In Germany, Switzerland, Austria, Sweden, Denmark, Norway, France and the USA, large numbers of geothermal heat pumps are already operational, and installation guidelines, quality control and contractor certification are now major issues of debate.
Single borehole heat exchanger (BHE) and arrays of BHE are modeled by using the finite element method. Applying BHE in regional discretizations optimal conditions of mesh spacing around singular BHE nodes are derived. Optimal meshes have shown superior to such discretizations which are either too fine or too coarse. The numerical methods are benchmarked against analytical and numerical reference solutions. Practical application to a borehole thermal energy store (BTES) consisting of 80 BHE is given for the real-site BTES Crailsheim, Germany. The simulations are controlled by the specifically developed FEFLOW–TRNSYS coupling module. Scenarios indicate the effect of the groundwater flow regime on efficiency and reliability of the subsurface heat storage system.
Infiltrating river water carries the temperature signal of the river into the adjacent aquifer. While the diurnal temperature fluctuations are strongly dampened, the seasonal fluctuations are much less attenuated and can be followed into the aquifer over longer distances. In one-dimensional model with uniform properties, this signal is propagated with a retarded velocity, and its amplitude decreases exponentially with distance. Therefore, time shifts in seasonal temperature signals between rivers and groundwater observation points may be used to estimate infiltration rates and near-river groundwater velocities. As demonstrated in this study, however, the interpretation is nonunique under realistic conditions. We analyze a synthetic test case of a two-dimensional cross section perpendicular to a losing stream, accounting for multi-dimensional flow due to a partially penetrating channel, convective-conductive heat transport within the aquifer, and heat exchange with the underlying aquitard and the land surface. We compare different conceptual simplifications of the domain in order to elaborate on the importance of different system elements. We find that temperature propagation within the shallow aquifer can be highly influenced by conduction through the unsaturated zone and into the underlying aquitard. In contrast, regional groundwater recharge has no major effect on the simulated results. In our setup, multi-dimensionality of the flow field is important only close to the river. We conclude that over-simplistic analytical models can introduce substantial errors if vertical heat exchange at the aquifer boundaries is not accounted for. This has to be considered when using seasonal temperature fluctuations as a natural tracer for bank infiltration.
The use of groundwater as a carrier of thermal energy is an important source of sustainable heating and cooling. However, the effects of thermal use on geochemical and biological aquifer characteristics are poorly understood. Here, we have assessed the impacts of heat discharge on an uncontaminated, shallow aquifer by monitoring the hydrogeochemical, bacterial and faunal parameters at an active thermal discharge facility. The observed variability between wells was considerable. Yet, no significant temperature impacts on bacterial or faunal abundance and on bacterial productivity were observed. Also, we did not observe an improved survival or growth of coliforms with temperature. In contrast, the diversity of bacterial terminal restriction fragment (T-RF) length polymorphism fingerprints and faunal populations was either positively or negatively affected by temperature, respectively, and the abundance of selected T-RFs was clearly temperature dependent. Canonical correspondence analysis indicated that both the impact of temperature and of surface water from a nearby river, were important drivers of aquifer biotic variability. These results demonstrate that aquifer thermal energy discharge can affect aquifer bacteria and fauna, while at the same time controlling only a minor part of the total seasonal and spatial variability and therefore posing no likely threat to ecosystem functioning and drinking water protection in uncontaminated, shallow aquifers.
An introduction to thermogeology: ground source heating and cooling Geothermal energy technology and current status: an overview
- References Banks
References Banks D (2008) An introduction to thermogeology: ground source heating and cooling. Wiley, Chichester, UK, 352 pp Barbier E (2002) Geothermal energy technology and current status: an overview. Renew Sust Energ Rev 6(1–2):3–65 5
Review of life cycle environmental effects of geothermal power generation Techno-economic and spatial analysis of vertical ground source heat pump systems in Germany
- Rybach P L Bayer
- P Blum
- Brauchler
Hydrogeology Journal (2014) 22: 1–6 DOI 10.1007/s10040-013-1082-0 Bayer P, Rybach L, Blum P, Brauchler R (2013) Review of life cycle environmental effects of geothermal power generation. Renew Sust Energ Rev 26:446–463 Blum P, Campillo G, Kölbel T (2011) Techno-economic and spatial analysis of vertical ground source heat pump systems in Germany. Energy 36:3002–3011
Reinjection in geothermal fields: a review of worldwide experience Propagation of seasonal temperature signals into an aquifer upon bank infiltration Review: Geothermal heat as a tracer of large-scale groundwater flow and as a means to determine permeability fields
- E Zarrouk
- O Sj
- Sullivan
- N Molina-Giraldo
- P Bayer
- P Blum
- Cirpka
- Oa
E, Zarrouk SJ, O'Sullivan MJ (2011) Reinjection in geothermal fields: a review of worldwide experience. Renew Sustain Energ Rev 15(1):47–68 Molina-Giraldo N, Bayer P, Blum P, Cirpka OA (2011) Propagation of seasonal temperature signals into an aquifer upon bank infiltration. Ground Water 49(4):491–502 Saar MO (2011) Review: Geothermal heat as a tracer of large-scale groundwater flow and as a means to determine permeability fields. Hydrogeol J 19(1):31–52
Current status of ground source heat pumps and underground thermal energy storage in Europe Sensible energy storage in aquifers: 1. theoretical study Sensible energy storage in aquifers: 2. field experiments and comparison with theoretical results
- Mendrinos D Sauty Jp
- Gringarten Ac
- A Menjoz
- Sauty Jp
- Fabris Ac H Gringarten
- D Thiery
- A Menjoz
- Landel
- Pa
B, Karytsas C, Mendrinos D, Rybach L (2003) Current status of ground source heat pumps and underground thermal energy storage in Europe. Geothermics 32:579–588 Sauty JP, Gringarten AC, Menjoz A, Landel PA (1982a) Sensible energy storage in aquifers: 1. theoretical study. Water Resour Res 18(2):245–252 Sauty JP, Gringarten AC, Fabris H, Thiery D, Menjoz A, Landel PA (1982b) Sensible energy storage in aquifers: 2. field experiments and comparison with theoretical results. Water Resour Res 18(2):253–265
Thermal use of shallow groundwater Underground mine water for heating and cooling using geothermal heat pump systems
- F P Bayer
- P Blum
- N Molina-Giraldo
- Kinzelbach
F, Bayer P, Blum P, Molina-Giraldo N, Kinzelbach W (2013) Thermal use of shallow groundwater. CRC, Boca Raton, FL, 266 pp Watzlaf GR, Ackman TE (2006) Underground mine water for heating and cooling using geothermal heat pump systems. Mine Water Environ 25(1):1–14