Open-loop Geothermal Systems Research Articles

A note on the analysis of groundwater travel times for injection-abstraction doublets

The solutions of Lippmann and Tsang (1980) for the temperature changes in an injection-abstraction doublet have been revisited as benchmarks for numerical simulations developed to assess the feasibility of open-loop geothermal systems. The Lippmann and Tsang (1980) solution for the evolution of the temperature at the abstraction well was developed for the case of no ambient groundwater flow in an aquifer that is sealed across its top and bottom. The results of testing confirm some puzzling aspects of the solution. In this note it is shown that while some elements of the Lippmann and Tsang (1980) solution are correct, results for the temperature history at an abstraction well deviate substantially from solutions presented elsewhere in the literature.

The role of pit lake thermal dynamics on the thermal performance of ground heat exchangers

The addition of ground heat exchangers (GHEs) to a pit lake’s basin has the potential for abundant, clean and renewable geothermal energy extraction using shallow geothermal systems. Basin-embedded GHEs avoid direct interaction with mine water, which has been shown to impact efficiency and longevity in mine open-loop geothermal systems negatively. The now accelerated closure of open-pit coal mines presents itself as an opportunity to use this technology. However, no guidelines currently exist for designing or operating GHEs embedded in the sediment of water bodies. Furthermore, the two-way coupling between the complex annual thermal fluid dynamics that lakes are naturally subjected to and heat fluxes on the sediments and the GHE system has not been explored. In this study, we develop and validate finite element models to assess the relevance of lake thermal stratification in the performance of a geothermal system embedded in water bodies basins, e.g., on open-pit mine closures, under temperate residential thermal loads. The results show that the pit lake’s role as a thermal sink improves significantly when the lake’s thermal dynamics are accounted for, with an increase of up to 292% in the lake’s available energy budget. A minor variation in energy budget (~8%) was found whether the lake is modelled explicitly or simplified as a transient Dirichlet temperature boundary condition. This small difference vanishes if horizontal circulation along the lake is considered, highlighting the lake’s thermal energy potential. Finally, the impact on the GHE Coefficient of Performance (COP) is evaluated, with a maximum of ~15% difference among all cases.

Numerical simulation on converting abandoned wells into double-well open-loop geothermal system

Converting abandoned oil wells into geothermal systems holds immense potential and has garnered international attention. However, research on converting abandoned oil wells into Open-Loop Geothermal Systems (OLGS) remains insufficient and requires further exploration. To address this gap, this study utilizes COMSOL software employing the Finite Element Method (FEM) to establish a numerical model of a double-well OLGS with 3D multi-physics field coupling, investigating geothermal extraction through numerical simulation. The findings indicate that in double-well OLGS, utilizing high flow rates in the early production stage and lower flow rates in the later stages enhances system thermal power. Additionally, employing lower inlet temperatures in the early production stage and higher inlet temperatures in the later stages favors geothermal extraction. Higher geothermal gradients and larger well spacings further benefit geothermal extraction. Increasing the length of the production well's insulating layer in the early production stage helps minimize heat loss. The outlet temperature exhibits high sensitivity to flow rate and geothermal gradient throughout the production phase, while sensitivity shifts towards inlet temperature and well spacing in the later stages. In the five-spot OLGS, outlet temperature and thermal power increase with a reduction in the number of production wells; moreover, assuming identical outlet temperatures (100 ℃) after 50 years of production, the thermal power of the five-spot OLGS exceeds that of the double-well OLGS by an average of 20937.88 kW per year.

Investigating heat transmission in a wellbore for Low-Temperature, Open-Loop geothermal systems

Heat transfer processes in geothermal wellbores are an essential component to overall system performance, but can be overlooked in subsurface modelling studies that tend to focus on reservoir response. This study addresses heat transfer in the wellbore through a comprehensive modelling study of 10 different parameters on OpenGeoSys software designed to evaluate heat losses during open-loop production conditions for typical low-temperature (<100 °C) single phase geothermal systems. Models were set-up to focus on wellbore effects only, using a single production well with constant fluid inlet temperature boundary condition. Results indicate that under base case conditions for a 2-km deep well surrounded by rock formations with a thermal conductivity of 2.5 W/(m.K) and bottom-hole temperature of 60 °C, the difference in inlet (reservoir) and production (wellhead) temperature at the end of a 40-year production period is 2.06 °C. This corresponds to minimum heat losses into the surrounding formations of −63.3 W/m, which is ∼ 7 % of the thermal power recorded at the wellhead (assuming a rejection temperature of 30 °C) and a 3.4 % difference to bottom-hole temperature. These losses in heat can be significant, particularly when in combination with surface losses through the heat exchanger or in the reservoir through thermal breakthrough. Wellbore insulation can reduce losses, but it would appear this only impacts the short-term. Wellbore performance can also be improved, with heat losses minimized, when developing wells above the reservoir interval in low thermal conductivity rock with high geothermal gradients.

A modified methodology to substitute U-shape well using a single well with fracture network: Design and performance

The increasing demand for low-carbon energy has led to the exploration of renewable energy sources, including geothermal energy. One potential method for accessing this energy is through the retrofitting of abandoned oil wells into geothermal wells. While there have been some previous efforts in this area, many of these methods suffer from low efficiency or high cost. In this study, we have proposed a novel retrofitting pattern for a single well embedded with an enhanced fracture system (EFS). Using COMSOL Multiphysics, a numerical model was established to investigate the effects of different reservoir and fracture properties on the performance of EFS. Our analysis showed that it is possible to replace a U-shaped well with a single well using EFS, and that the thermal power was more than four times greater than that of conventional borehole heat exchangers over a 50-year heat extraction period. We found that fracture permeability and aperture were the two most critical parameters for achieving high heat extraction performance in EFS. EFS exhibits significantly better performance compared to the traditional open-loop geothermal system (OLGS). Based on our findings, we recommend controlling the flow rate within the range of 10–20 kg/s and pumping proppant for optimal EFS design.

Influence of extreme fracture flow channels on the thermal performance of open-loop geothermal systems at commercial scale

Adequate stewardship of geothermal resources requires accurate forecasting of long-term thermal performance. In enhanced geothermal systems and other fracture-dominated reservoirs, predictive models commonly assume constant-aperture fractures, although spatial variations in aperture can greatly affect reservoir permeability, fluid flow distribution, and heat transport. Whereas previous authors have investigated the effects of theoretical random aperture distributions on thermal performance, here we further explore the influence of permeability heterogeneity considering field-constrained aperture distributions from a meso-scale field site in northern New York, USA. Using numerical models of coupled fluid flow and heat transport, we conduct thermal–hydraulic simulations for a hypothetical reservoir consisting of a relatively impervious porous matrix and a single, horizontal fracture. Our results indicate that in highly channelized fields, most well design configurations and operating conditions result in extreme rates of thermal drawdown (e.g., 50% drop in production well temperatures in under 2 years). However, some other scenarios that account for the risks of short-circuiting can potentially enhance heat extraction when mass flow rate is not excessively high, and the direction of geothermal extraction is not aligned with the most permeable features in the reservoir. Through a parametric approach, we illustrate that well separation distance and relative positioning play a major role in the long-term performance of highly channelized fields, and both can be used to help mitigate premature thermal breakthrough.

Mine water as a source of energy: an application in a coalfield in Laciana Valley (León, NW Spain)

Mine water can be a renewable and economical source of geothermal and hydraulic energy. Nine discharges from closed and flooded coal mines in the Laciana Valley (León, NW Spain) have been studied. Various technologies for the energy use of mine water, as well as the influence of factors such as temperature, the need for water treatment, investment, potential customers and expansion capacity, have been evaluated by means of a decision-making tool. It is concluded that the most advantageous option is an open-loop geothermal system using the waters of a mountain mine, the temperature of which exceeds 14 °C and whose distance to customers is less than 2 km. A technical–economic viability study for a district heating network designed to supply heating and hot water to six public buildings in the nearby town of Villablino is presented. The proposed use of mine water might help areas that have been greatly affected socioeconomically by the closure of the mines and has other advantages compared to conventional energy systems, such as the reduction of CO2 emissions.Graphical It showing the advantages of using mine water as an energy source for district heating and a simplified layout.

Modelling Interactions between Three Aquifer Thermal Energy Storage (ATES) Systems in Brussels (Belgium)

Shallow open-loop geothermal systems function by creating heat and cold reserves in an aquifer, via doublets of pumping and reinjection wells. Three adjacent buildings in the center of Brussels have adopted this type of aquifer thermal energy storage (ATES) system. Two of them exploit the same aquifer consisting of Cenozoic sands, and started operation in 2014 and 2017, respectively. A previous hydrogeological model developed by Bulté et al. (2021) has shown how the thermal imbalance of one of the systems jeopardizes the thermal state of this upper aquifer. Here, the interactions with a more recent third ATES system located in the deep aquifer of the Palaeozoic bedrock are studied and modelled. After being calibrated on groundwater flow conditions in both aquifers, a 3D hydrogeological model was used to simulate the cumulative effect of the three geothermal installations in the two exploited aquifers. The results of the simulations showed that although the hydraulic interactions between the two aquifers are very weak (as shown by the different observed potentiometric heads), heat exchanges occur between the two aquifers through the aquitard. Fortunately, these heat exchanges are not sufficient to have a significant impact on the efficiency of the individual geothermal systems. Additionally, this study shows clearly that adding a third system in the lower aquifer with a mean power of 286 kW for heating between October and March and an equivalent mean cooling power between April and September is efficient.

Factors affecting the efficiency of closed-loop geothermal wells

Geothermal energy has a promising prospect of becoming a feasible source of clean energy in the future. However, conventional open-loop geothermal systems need continuous water circulation, which limits their application in dry areas. On the other hand, long-term fluid injection into the reservoir may cause issues such as seismicity. To overcome these shortcomings, closed-loop geothermal systems are not requiring water withdrawal or water injection. However, the mechanism controlling the efficiency of closed-loop systems has not been well analyzed. To resolve the issue, a systematic study was conducted on factors affecting production efficiency of a closed-loop geothermal well. First, a coupled three-dimensional model was established, which was then validated against experimental results available in the literature. Using this model, the effects of several critical design factors were investigated quantitatively. These factors include cement thermal conductivity, cement thickness, fluid circulation rate, injected fluid temperature, heat capacity of circulating fluid, heat exchanger height, and tubing outer diameter. Our simulation results indicate that increasing the cement thermal conductivity enhances both produced fluid temperature and thermal power. The effect of cement thickness is correlated with the value of its thermal conductivity. As the circulation rate increases, the temperature of produced fluid decreases while thermal power increases asymptotically. Using a circulating fluid with high heat capacity would result in higher thermal power. A large heat exchanger height would boost both the production temperature and thermal power significantly. Finally, a dimensionless analysis was conducted, through which two dimensionless numbers were derived to integrate the effects of different factors. By comparison analysis, the accuracy of the dimensionless numbers was validated. Also, the impact of the dimensionless numbers on dimensionless produced fluid temperature was determined. With the dimensionless numbers, the effects of different individual factors can be evaluated comprehensively, which brings convenience to parameter design. The potential applications of the derived dimensionless numbers in parameter design of closed-loop systems were discussed. Results and conclusions obtained in this paper may provide a reference for optimally designing closed-loop systems.

A method to evaluate the performance of an open loop geothermal system for mine water heat recovery

Purpose. To develop a method to evaluate hydrodynamic and thermal parameters of an open loop geothermal system with the discharge into surface water bodies as well as to test the method under real site conditions considering different technology options, geotechnical and thermodynamic factors. Methodology. We employed the relations of hydraulics and thermodynamics, performed an engineering review of open loop geothermal systems for mine water heat recovery, studied hydrodynamic and mining conditions of the colliery Novohrodivska No.2. The developed technique includes evaluating the temperature of rocks around flooded workings, the length of the hydraulic path and flow resistance of workings. Findings. The evaluated temperature of mine water entering on-ground heat exchangers ranges at 17.8 0.25 C, and the system thermal output is 1070 21 kW. Water temperature in flooded workings due to dilution with infiltration during the operation period of 25 years is expected to fall by 0.61.0 C, which decreases the thermal output by 5.68.3%. The estimated cooling of water during its rise in the shaft does not exceed 1C. The criterion of the geothermal system energy efficiency decreases from 1.8 when pumping close to the mine water level to 1.05 when pumping 460 m below the ground; the heat pump coefficient of performance (COP) reaches 5.0. Originality. The flow characteristics and hydraulic flow lengths at different horizons, the temperature of rocks around workings were found to be the dominant factors for the thermal output under steady flow. The pumping depth was proved to significantly affect the energy efficiency of the system. Practical value. The proposed method allows quantifying the energy criterion of an open loop geothermal system with the discharge into surface watercourses, which enables optimizing system performance indicators.

Mitigation of groundwater iron-induced clogging by low-cost bioadsorbent in open loop geothermal heat pump systems

Green energy production from natural resources can reduce emissions of greenhouse gases and pollutants from burning of fossil fuels in power plants. Recently, groundwater geothermal energy (GGE) is harnessed by deploying closed- and open-loop heat systems. In open-loop geothermal heat pump systems (OLGHPS), groundwater is reinjected into aquifer after harnessing GGE. Nevertheless, OLGHPS face noxious clogging issue because of elusive chemistry (corrosion or precipitation) of chemical species, principally of iron (Fe), in pipes and aquifers during reinjection process via oxidation reactions. Plethora of filtering materials are available for removal of ions, but these are quite expensive and environmentally unsafe. More recently, low-cost, eco-friendly, green filtering materials gain much interest. These materials can remove ions from groundwater that can minimize clogging in heat exchange systems, injection wells, and aquifer. In the present study, three filtering materials, i.e., wooden charcoal (biomaterial), yamazuna fine sand, and volcanic ash, were tested to estimate their Fe removal capacity. In upward flow mode with minimum oxygen-water contact, serial column (each with 6 ports) experiments were conducted under constant pressure head and constant velocity conditions. Columns were connected to well water having dissolved Fe concentration of 10.85 mg L−1. Sampling was done at the well, column inlets, column’s six sampling ports and column outlets, and samples were analyzed for Fe by atomic absorption spectroscopy. Related tested parameters include pH, EC, temperature, turbidity, porosity, particle diameter, and dissolved oxygen. Volcanic ash showed less Fe removal, while sand filter showed substantial reduction in velocity. Biomaterial (wooden charcoal) displayed higher Fe adsorption capacity compared to other materials that can be ascribed to its surface chemistry and functional groups. Under different flow rates, maximum Fe content of 3.5 g Fe kg−1 dry charcoal was obtained. By considering a safety factor and influence of groundwater composition, it is possible to design a biomaterial-based iron filter system to minimize Fe-induced chemical clogging in OLGHPS which is an eco-friendly, green energy source.

ПОРІВНЯЛЬНИЙ АНАЛІЗ ГЕОТЕРМАЛЬНОГО ПОТЕНЦІАЛУ ЗАКРИТИХ ШАХТ ДОНЕЦЬКОГО ТА РУРСЬКОГО ВУГІЛЬНИХ БАСЕЙНІВ

Purpose. This study aims to perform a comparative analysis of the geothermal potential for closed mines in the Donbas and Ruhr regions in terms of the operation efficiency of geothermal systems of various types. Methods. The proposed approach includes ranking closed mines in the Ruhr (Germany) and Donetsk (Ukraine) coalmining areas according to the major parameters of geothermal system efficiency that includes the maximum and net thermal capacity, heat pump coefficient of performance COP, energy efficiency of heat recovery. The last parameter, introduced by the authors earlier, is defined as the ratio of the produced thermal energy to the thermal equivalent of the electricity required for running the heat pumps and the heat transfer fluid circulation. Results. The average expected thermal capacity of open loop geothermal systems at mine drainages in Germany was found higher than the similar indicator for the selected mine drainages in Ukraine, with slightly lower indicators of mine water heat recovery compared to the drainages in the Donbas. The average expected thermal capacity of closed loop geothermal systems based on coaxial probes at the current water level in the mines of two areas is estimated to be within the range of 30-34 kW, and the average indicators of geothermal heat recovery in the mines of two areas differ by no more than 5%, while the mines in the Donbas demonstrate a higher dispersion of calculated indicators. Similarity of operating conditions and energy efficiency indicators of geothermal systems evaluated for two areas indicates the feasibility and the potential of operating such systems in Ukraine. Scientific novelty. The approach to ranking of closed mines according to their geothermal potential based on parameters of mine water heat recovery efficiency has been substantiated and implemented. The developed approach enables identifying the promising sites to install geothermal systems of various types at inactive mines. Practical significance. The proposed approach allows to preliminarily evaluate the ranges of indicators for the effective operation of geothermal systems of various types with identification of the most promising areas for further detailed technical and economic justifications.

The impact of porous medium heterogeneity on the thermal feedback of open-loop shallow geothermal systems

Groundwater has been increasingly used to provide low-carbon heating and cooling of buildings with open-loop shallow geothermal systems. Water is generally reinjected into the same aquifer after the heat exchange in order to avoid the aquifer depletion. However, this can result in the return of part of the injected water to the production well(s), causing a gradual thermal alteration known as thermal feedback. Thermal feedback is a major design issue of open-loop shallow systems but, so far, it has been mainly addressed neglecting the heterogeneity of the aquifer properties. This study investigates the impact of aquifer heterogeneity on two main metrics that characterize thermal feedback: thermal breakthrough time (i.e., the first arrival time of the thermal plume) and recirculating ratio (i.e., the fraction of water coming back to production well). A stochastic approach was adopted performing a large number of numerical simulations that cover a wide range of possible scenarios. The results highlight that conductivity heterogeneity plays a major influence on the temperature evolution at the production well. The breakthrough time alone might lead to misleading evaluations of the system efficiency, given that a few particles can reach the production well by traveling in the highly-conductive layers. Conversely, both the heterogeneity and the thermal dispersivity have a negligible impact on the recirculating ratio, which quantifies the long-term evolution of thermal feedback. As a consequence, the available approaches based on advection-only and homogeneous medium are a robust tool to predict the long-term behavior of shallow open-loop geothermal systems.

Heat extraction study of a novel hydrothermal open-loop geothermal system in a multi-lateral horizontal well

The efficient development of hydrothermal resource is an important focus in the global geothermal industry. A novel hydrothermal open-loop geothermal system in a multi-lateral horizontal well is presented to achieve the simultaneous exploitation of multi-layer reservoirs and accelerate the large-scale development of the hydrothermal resource. To investigate the detailed performance of the novel geothermal system, a novel 3D fluid flow and heat transfer numerical model is established based on the local thermal non-equilibrium and dual porosity theories. The flow and temperature fields are analyzed, while the pressure and temperature interferences between the lateral wellbores of the multi-lateral horizontal well system are comprehensively investigated. The influences of the injection flow rate, lateral-wellbore number, spacing between the injection segment and the main wellbore, fracture aperture on the heat extraction are studied. Furthermore, the thermal characteristics of the novel geothermal system and traditional doublet well system are compared for the first time. The investigation indicates that the flow impedance of the novel geothermal system can decrease by 75.38%, and its energy efficiency reaches 8 times that of the doublet well system. The findings can provide a key reference for scientific research and application of the novel and traditional geothermal systems.

Environmental impacts of aquifer thermal energy storage (ATES)

Aquifer Thermal Energy Storage (ATES) is an open-loop geothermal system allowing long-term storage of thermal energy in groundwater. It is a promising technology for environmentally friendly energy generation that can reduce greenhouse gas (GHG) emissions. In the literature, there are few studies on the greenhouse gas emissions caused by ATES systems over their entire life cycle. Thus, this study presents a novel life cycle assessment (LCA) regression model that can be used for a wide range of ATES configurations due to its parametric structure. This model is a fast alternative to conventional time-consuming LCAs. Combined with a Monte Carlo simulation, it enables the analysis of the environmental impacts of a large variety of hypothetical ATES systems and therefore the evaluation of the technology as a whole. Compared to conventional heating systems based on heating oil and natural gas, the median value of the Monte Carlo simulation results in GHG savings of up to 74%. In comparison to cooling techniques using today's electricity mix, ATES can save up to about 59% of GHG emissions, while also being economically competitive. When considering a projected electricity mix for the year 2050, the GHG emission savings resulting from a second LCA regression model are as high as 97%. The findings of our sensitivity analysis show which ATES design parameters should be optimized when planning new systems. In particular, the most important design parameters operating time cooling and coefficient of performance (COP) of the heat pump should be carefully considered.

Analysis of flow and thermal breakthrough in leaky downhole coaxial open loop geothermal system

Geothermal energy is crucial to energy transformation; however, the difficulty of reinjection and the low efficiency of heat extraction need to be solved urgently. Coaxial tube heat exchanger has no difficulty of reinjection, but the averaged heat output per unit length is very limited. A new type of leaky downhole coaxial open loop geothermal system using the technique of “no water withdrawn but heat only” is proposed, which makes full use of the convective heat transfer of the aquifer and the leakage characteristics of the aquitard. From the test, heat output is up to 930 kW, which is 3.5 times that of the traditional coaxial casing, which is a promising geothermal heat extraction technique. In this study, a coupled analytical and numerical simulation model of wellhole aquifer flow and heat transfer was established to study the heat extraction performance, as well as the flow and thermal breakthrough of the system. Through the analysis of calculation results and the introduction of critical Rayleigh number, which represents the degree of convection and heat conduction, the optimal correlation between the thickness of the aquitard, injection temperature, flow rate, and permeability ratio is established. Regarding the base case thickness of the aquitard, a value of 19.51 m was suggested, and Kratio ≥ 20 was suggested regarding the reservoir structure, which provides quantitative guidance and is significant for system optimization design.

Comparison of production characteristics of various coaxial closed-loop geothermal systems

The effective exploitation of deep geothermal resources has been a research focus in the geothermal industry. The coaxial closed-loop geothermal system (CCGS) is expected to be the most feasible technique for developing deep geothermal resources in the form of closed-loop circulation. It avoids high-cost fracturing and environmental problems, making it preferable when compared with the open-loop geothermal system. Current studies mainly focus on the thermal performance of the CCGS with one well type. However, the comprehensive performances of various CCGSs have a noticeable difference in geothermal energy exploitation. It is essential to implement a detailed comparative analysis of various CCGSs to determine the production characteristics and enable their application. In this study, a 3D transient thermal–hydraulic model considering the effect of fluid gravity and viscous friction in the wellbore is proposed to realise a CCGS comprehensive investigation. The temperature field, energy, flow, and economic characteristics of the CCGSs with vertical-well, horizontal-well, and multilateral-well types are compared. To confirm the efficacy of the CCGS, the energy, flow and economic efficiencies are introduced. The results indicate that fluid gravity is beneficial for decreasing the injection pressure and pump consumption. The fluid viscous friction is important for the CCGS energy, flow, and economic performances. The precedence order obtained in terms of the long-run efficiency for the application is multilateral-well CCGS > vertical-well CCGS > horizontal-well CCGS. The key findings offer a significant reference for the CCGS scientific study.

Production performance of a novel open loop geothermal system in a horizontal well

A novel open-loop geothermal system (OLGS) in a horizontal well is proposed to achieve efficient and large-scale development of hydrothermal resources. Compared with the vertical-well extracting groundwater system, drilling and completion costs can be significantly reduced by accomplishing fluid injection and production in one horizontal well. The horizontal-well OLGS showed improved performance and can have broader application prospects than the vertical-well extracting groundwater system and conventional vertical-well OLGS, particularly in not-so-thick reservoirs. Therefore, the horizontal-well OLGS is expected to be useful in accelerating the exploitation of hydrothermal resources. Although some OLGS studies have been reported, no comprehensive parameter analysis of the OLGS has been performed until now, which hinders its application. In this study, a 3D unsteady-state model based on local thermal non-equilibrium is established and validated using an analytical model. Results show that variations in the pressure and flow behaviour generally occur within 50 m near the wellbore, whereas the maximum impact scope of the cooling region is 85 m, serving as the critical value for the fracturing operation region and well-spacing design. The influence of dominant engineering and reservoir parameters on the production temperature, heat output, fluid injection, and production were investigated. Sensitivity evaluation was performed to compare the effects of various parameters. Furthermore, the performances of OLGS with horizontal and vertical wells were compared for the first time, indicating that the horizontal-well OLGS can achieve improved performance via a long horizontal well. The results can offer guidance for application designs of the horizontal-well OLGS and traditional vertical-well OLGS. Furthermore, they can promote the rapid development of horizontal-well technology for the exploitation of geothermal resources.

Risk assessment for open loop geothermal systems, in relation to groundwater chemical composition (Ljubljana pilot area, Slovenia)

Risk assessment for open loop geothermal systems, in relation to groundwater chemical composition (Ljubljana pilot area, Slovenia)

Impact of groundwater heat pump systems on subsurface temperature under variable advection, conduction and dispersion

The number of worldwide installed groundwater heat pump (GWHP) systems is approaching one million units. This increase in GWHP systems creates an increasing competition for groundwater use. Thus, we have simulated the long-term thermal impacts of such open-loop geothermal systems with numerical heat transport models, by studying the role of flow and heat transport parameters. The focus is set on transient conditions evolving over decades of seasonally imbalanced heat injections in aquifers with differing ambient flow regimes. The results demonstrate the existence of plume length peaking in moderate groundwater flow velocities (0.5–1.0 m d−1). The longitudinal and transverse dispersivity coefficients have a strong influence on the plume extension and on transient development. Reducing the injected temperature difference allows the control of the maximum temperature reached in the plume but implies a considerable hydraulic influence. Comparisons with numerical simulations, using an average of the thermal load, shows that the flow velocity and dispersity coefficients strongly condition the relevance of such simplified approaches. In addition, if satisfactory results are obtained for seasonal or long-term estimations, those for intermediate lengths of time are insufficient. This study contributes to improving the overall understanding of key elements involved in the thermal impact and the development of GWHP systems.