Abstract This study evaluates the geothermal potential of the Akiri Hot Spring (AHS) region, Middle Benue Trough (MBT), Nigeria, using airborne magnetic data. Advanced geophysical processing techniques were employed to analyze the subsurface structures and identify geothermal reservoirs of the region by revealing the fault zones, delineating the lithological variations, and mapping the structural discontinuities critical for assessing thermal energy prospects zones of the region. Qualitatively, the magnetic anomaly map reveals lithological variation with magnetic intensity values ranging − 31.4–117.3 nT. Low magnetic intensity values (< 23.7 nT) were found around the AHS region, while high-intensity values (> 78.2 nT) found in the north and eastern regions. Low Analytic Signal (AS) values (< 0.001 nT/m) were observed around the Akiri region, and they were linked to the alluvial sandstones of the Pliocene age, whereas higher AS values (> 0.007 nT/m) are revealed in the southeastern regions of the research area and it is an indicative of intrusive rock bodies. Quantitative investigation using spectral analysis reveals depth to top $$\left( {d_{{{\text{top}}}} } \right)$$ d top and depth to centroid $$\left( {d_{c} } \right)$$ d c (ranging from 0.587 ± 0.015 to 1.106 ± 0.038 km and 4.830 ± 0.048–6.150 ± 0.044, respectively). The calculated Curie point depth $$\left( {d_{{{\text{CP}}}} } \right)$$ d CP and heat flow ranges from 8.559 ± 0.046 to 11.380 ± 0.059 km and 124.700–129.6 mW/m 2 , respectively. A three-dimensional model integrating $$d_{{{\text{top}}}}$$ d top and $$d_{{{\text{CP}}}}$$ d CP highlights a heat flow depression in the vicinity of AHS, where $$d_{{{\text{CP}}}}$$ d CP has an average depth of approximately 10.2 km. High heat flow values in the AHS region indicate significant geothermal energy potential, possibly linked to magmatic activity, fault zones, or deep-seated thermal anomalies. Euler deconvolution indicates dominant E–W structural trends, with minor NE–SW orientations. Findings highlight substantial geothermal potential, driven by subsurface anomalies and faulting. This study enhances the understanding of geothermal systems in the MBT and provides a framework for exploring similar volcanic regions across Africa.

Abstract Geothermal energy is a promising solution to meet the increasing global energy demand while mitigate climate change. In recent years, the utilization of carbon dioxide (CO2), especially supercritical CO2 (SCCO2), for geothermal energy recovery has attracted increasing attention. This study introduces and simulates a modified cyclic SCCO2 injection method for geothermal energy recovery, marking the first exploration of its kind. We analyzed the SCCO2 injection process under various well patterns and injection modes, comparing the cumulative energy recovery performance of cyclic and continuous injection across different models. Our findings revealed that the original reservoir dominates the initial energy production until the SCCO2 breakthrough. After the breakthrough, cyclic injection should be utilized to enhance energy production, with higher heat extraction efficiency and the mitigation of the thermal breakthrough effect. In addition, our findings suggest that an optimal combination of cyclic and continuous injection can leverage the advantages of both strategies. Through further optimization, modified cyclic SCCO2 injection method enhances energy production, achieving up to a 59% improvement in cumulative energy production (4.155E14J) and a 200% increase in NPV ($600,000) compared to baseline scenarios, with higher heat extraction efficiency and mitigation of thermal breakthrough effects.

Co-production of geothermal energy and lithium is an emerging opportunity with the potential to enhance the economic potential of geothermal operations. The economic reward of extracting lithium from geothermal brine is determined by how the lithium concentration evolves during brine production. In the initial stage, production will target lithium contained in the brine resident close to the production well. While lithium recharge, in the form of rock dissolution and inflow from other parts of the reservoir, is possible, the efficiency of such recharge depends on the geology of the reservoir. In this work, we study how structural heterogeneities in the form of fractures impact the flow of lithium-carrying brine. Using a simulation tool that gives high resolution of flow and transport in fractures and the host rock, we study how the presence of fractures influences energy and lithium production. Our simulations show that, due to heat conduction and the lack of mineral recharge from the rock, differences in fracture network geometries have a much larger impact on lithium production than energy production. The simulations thus confirm that in addition to the geochemical characterisation of lithium in geothermal brines, understanding fracture characterisation and its impact on production is highly important for lithium production.

As a crucial solution to the challenge of limited urban underground space development, the assembled shaft offers extensive structure–soil contact surfaces and meantime holds significant potential for shallow geothermal energy exploitation. In this paper, we propose an assembled energy shaft, i.e. a novel geothermal development system, in which the heat exchanger could be easily installed in the shaft concrete with extensive soil–contact area and can have superior protection without extra pre-drilling. This paper establishes a heat transfer model for energy shafts in soft soil areas. By comparing the heat transfer efficiency and additional thermal stress of the energy tunnel in Beijing, the practical feasibility of constructing energy shafts in coastal cities is demonstrated. By proposing the characterization parameters of heat exchange capacity per unit lining surface area and heat exchange per unit length of pipe, it is revealed that thermal interference is minimized when the heat exchange pipe spacing of the energy shaft is 0.25–0.3 m. The heat exchange efficiency is increased when the fluid flow rate is 0.6 m/s ~ 0.9 m/s. According to the deformation characteristics of the lining, the maximum tensile and compressive stresses occur near the inlet of the heat exchange pipe. To minimize stress concentration, it is advisable to position the inlet of the heat exchange pipe at the center of the segment. The research findings confirm the substantial potential of assembled energy shafts in shallow geothermal development and provide valuable insights for the design of such shafts in coastal cities.

Geothermal energy could be used to reduce or replace diesel for heating in remote northern communities. Geothermal development has primarily focused on shallow, high-temperature resources, but interest in low-temperature and deep geothermal resource exploration has increased as energy costs and climate change policy have evolved. Here, we evaluated the low-temperature geothermal favourability in southwestern Yukon by adapting Play fairway analysis to data-scarce regions. Play fairway analysis is a spatial statistical tool that uses a layered data approach to model favourability and risk assessments for resource exploration. Previous Play fairway analyses concentrate on the physical aspects of geothermal favourability: heat, permeability, and fluid availability. This study presents an overview of potential direct and indirect physical parameters that could be used in a geothermal Play fairway analysis in data-scarce regions and introduces the importance of considering socio-economic data in the exploration phase. The socio-economic controls are grouped into quantitative and qualitative parameters that describe population trends and community interests. The framework presented is then applied to a Play fairway analysis for southwestern Yukon. Based on the physical and socio-economic analysis, there is interest in exploring geothermal potential along the Denali fault near Duke River to support the community of Burwash Landing.

A serious issue with geothermal power plants is the loss of production and decline in power plant efficiency. Scaling, also known as mineral precipitation, is one of the frequently-observed issue that causes this loss and decreasing efficiency. It is heavily observed in the production wells when the geothermal fluid rises from the depths due to a change in the fluid’s physical and chemical properties. Scaling issue in geothermal power plants result in significant output losses and lower plant effectiveness. In rare instances, it might even result in the power plant being shut down. The chemistry of the geothermal fluid, non-condensable gases, pH, temperature and pressure changes in the process from production to reinjection, power plant type and design, and sometimes the materials used can also play an active role in the scaling that will occur in a geothermal system. ICP–MS was used to evaluate the chemical properties of the fluids. On the other hand, XRD, XRF and SEM were used to investigate the chemical and mineralogical compositions of the scale samples in analytical methods. For the numerical approach, PhreeqC and GWELL codes were used to follow the chemical reactivity of the geothermal fluid in Tuzla production well. The novelty of this study is to determine potential degassing point and to characterize the mineralogical assemblage formed in the well because of the fluid composition, temperature and pressure variations. During production, geothermal fluids degas in the wellbore. This causes a drastic modification of the chemistry of the Tuzla fluids. This is why it is focused the calculations on the nature of the minerals that are able to precipitate inside the well. According to simulation results, the degassing point is estimated to be about 105 m depth, consistent with the field observations. If a small quantity of precipitated minerals is predicted before the boiling point, degassing significantly changes the fluid chemistry, and the model predicts the deposition of calcite along with smaller elements including galena, barite, and quartz. The simulation results are consistent with the mineral composition of scaling collected in the well.

This study reports on newly acquired density data of synthetically prepared pure and mixed NaCl and CaCl2 aqueous solutions that span a wide range of geothermally encountered concentrations and mixing ratios. The analytical data are provided for the temperature range of 293–353 K at ambient pressure. For the reproduction of that data, PHREESCALE was used. The predictive potential of this numerical tool regarding the density of geothermal fluids of known composition was the major target herein. As a result, the measured data are in good agreement with previous analytical studies found in the literature. Possible sources of errors are discussed in this paper. Density data of the mixed solutions at temperatures other than ambient are unique and close existing data gaps. The numerical model reproduces the newly measured and already existing density data within an error band of approximately 1%. For further use in geothermal applications, this can be considered an excellent agreement. Moreover, the model yields a direct calculation of density without the need to establish complex empirical equations of state and mixing rules. Finally, sensitivity calculations performed with a thermal–hydraulic (TH) numerical reservoir model demonstrate the required accuracy of fluid density for reliably predicting the long-term performance of deep geothermal energy systems. In terms of the productivity index and the timing of thermal breakthrough it shows that the present analytical and numerical uncertainty in density is small enough to reliably state both reservoir parameters.

This study investigates the feasibility to repurpose wells from gas production for geothermal closed-loop application in the North German Basin (NGB). The objective for this research topic is to extend the value-added chain of idle wells by re-completion as coaxial deep borehole heat exchangers as an efficient way to produce green energy without drilling new wells by saving the carbon emission and costs of building a new geothermal well. With numerical models of two typical geological settings of the NGB and two different completion schemes, it is possible to simulate the thermal performance over a lifetime of 30 years. The calculated heat extraction rates range from 200 to 400 kW, with maximum values of up to 600 kW. Sensitivity analyses demonstrate that re-completion depth and injection temperature are the most sensitive parameters of thermal output determination. The heat demand around the boreholes is mapped, and heat generation costs are calculated with heating network simulations. The initial production costs for heat are comparable to other renewable energy resources like biomass and competitive against gas prices in 2022. This study highlights available geothermal resources’ environmental and economic potential in already installed wells. The application has almost no geological and no drilling risks and may be installed at any idle well location.

Renewable energies, such as solar and wind, traditionally suffer from temporal incongruity. Society’s energy demand peaks occur at different times of day than the electricity generation potential of a photovoltaic panel or, often, a wind turbine. Heat demand, in particular, is subject to a significant mismatch between the availability of heat (in the summer) and the need for heat (in the winter). Thus, a future energy system design should incorporate underground thermal energy storage (UTES) to avoid this temporal mismatch and emphasize thermal applications. Such a basis of design would introduce new methods of energy arbitrage, encourage the adoption of geothermal systems, and decrease the carbon intensity of society. UTES techniques are becoming increasingly sophisticated. These methods of storage can range from simple seasonal storage for residential structures in a grouted borehole array (BTES), to aquifer thermal energy storage (ATES), deep reservoir storage (RTES) in basins, among others. The method that each of these techniques shares is the use of the earth as a storage medium. UTES can also be characterized for electricity production, but this work largely explores applications in heating and cooling, further limited in scope to sensible heat storage (SHS). Heating and cooling processes—residential, commercial, and industrial—make up large fractions of energy demand in North America. This is also true of other locales. With the increasing concerns of climate change, exacerbated by anthropogenic greenhouse gas emissions, developers and municipal planners are strategizing to decarbonize building heating and cooling at district scales. This review covers the integration of UTES techniques with thermal energy network (TEN) technology across large districts. Though storage has long been in use for conventional district heating networks, designs are rapidly innovating, indicating broader applications of UTES integration with a TEN is advantageous from both an efficiency and economic perspective. This rapid innovation indicates the need for the integrated review offered in this paper.

The use of geothermal energy is spreading globally due to its many advantages, especially for heating and cooling. The correct design of a geothermal system requires knowledge of the parameters of the subsoil rocks, and particularly the thermal conductivity (k), which is the intrinsic ability of a material to transfer thermal energy as a result of a temperature gradient. A thermal conductivity map of the geological formations is time-consuming to produce, but can be of great help when selecting the location of a low-enthalpy geothermal installation, resulting in significant savings and an increase in the efficiency of that installation. The preferred option for determining k is an in situ thermal response test, but laboratory methods may be an alternative if it is not available or affordable. In this work, the needle thermal probe method has been used to measure the k of representative outcropping rocks in Oviedo (NW Spain), since it allows to obtain a rapid determination, its cost is comparatively low and it can be implemented in a portable device. 162 measurements have been carried out on a total of 27 samples, ranging from 0.2 (clay) to 5.4 W m−1 K−1 (quartzite). A relationship has been found between the k of the rocks and their characteristics, such as mineralogy, anisotropy or geological age and a thermal conductivity map was created.