Exploitation Of Geothermal Energy Research Articles

Monitoring microseismicity of the Hengill Geothermal Field in Iceland

Induced seismicity is one of the main factors that reduces societal acceptance of deep geothermal energy exploitation activities, and felt earthquakes are the main reason for closure of geothermal projects. Implementing innovative tools for real-time monitoring and forecasting of induced seismicity was one of the aims of the recently completed COSEISMIQ project. Within this project, a temporary seismic network was deployed in the Hengill geothermal region in Iceland, the location of the nation’s two largest geothermal power plants. In this paper, we release raw continuous seismic waveforms and seismicity catalogues collected and prepared during this project. This dataset is particularly valuable since a very dense network was deployed in a seismically active region where thousand of earthquakes occur every year. For this reason, the collected dataset can be used across a broad range of research topics in seismology ranging from the development and testing of new data analysis methods to induced seismicity and seismotectonics studies.

Deep geothermal energy extraction, a review on environmental hotspots with focus on geo-technical site conditions

Knowledge about the environmental impacts of geothermal energy is important for understanding the role this technology could play in the transition towards sustainable energy production systems. In this study 30 life cycle assessment (LCA) studies on geothermal energy plants were reviewed, focusing on the major environmental hotspots and the cause-effect relationships between the geo-technical parameters and these environmental impacts. The variability in the reported environmental impacts is explained, and a more transparent picture of the geological, design and technical factors causing these impacts is provided by triangularly evaluating the reported results based on the plant's geo-technical characteristics (such as, well depth and geofluid temperature), the life cycle inventory, and the hotspot analysis results. The study focuses on six impact indicators that have been identified as high priority for geothermal energy by the GEOENVI project, as well as the water consumption impact. The results indicate that the impacts vary in magnitude and across different life cycle phases. Apart from the type of energy conversion technology used, differences in the geological and design parameters also introduce large variability in the impact results reported in the literature. Furthermore, all the reviewed LCAs adopt a static approach. Therefore, we present a research agenda that highlights the need to perform dynamic LCAs on geothermal energy exploitation plants to consider the changing context in which these technologies are operating.

Air quality in post-mining towns: tracking potentially toxic elements using tree leaves

In this study, leaves of the evergreen holm oak Quercus ilex were used to assess airborne contamination of potentially toxic elements (PTEs) at five towns located on the slopes of the Mt. Amiata (central Italy), an area with a long history of mining and, more recently, an important district for the industrial exploitation of geothermal energy. PTE composition and covariance of washed and unwashed Q. ilex leaves of three different ages (6, 12 and 24 month-old) were used to identify atmospheric inputs of PTEs at residential areas, evaluate long-term adsorption and retention of PTEs by the leaves, thus providing an indication of potential human exposure. Moreover, the determination of foliar concentrations of major elements (C, N, S and P) allowed an assessment of the nutritional status of the investigated urban tree stands which excluded the existence of stress condition caused by air pollution or other disturbances. Results indicated that overall Pb, Cu, and Cd concentration were low in the investigated urban sites, if compared with similar studies conducted in larger Italian cities, denoting a low contribution of vehicular traffic to the atmospheric pathway. The five urban settlements were characterized by a specific profile of elements (Al, Ba, Hg and Sb) enriched in unwashed leaves, resulting from the distinct geochemical characteristics of the area and from diffuse (i.e., urban activity) and point sources of PTEs emission (i.e., brownfields, geothermal power plants). The latter sources primarily govern the distribution of Hg, whose contamination was found to be very localized close to a major abandoned mining area. Our data provided quantitative evidence of the spectrum of PTEs potentially impacting resident population and may prove useful in support of follow-up instrumental monitoring campaigns of air quality, as well as for human health and ecological risk assessments.Graphical abstract

Geochemical and Isotopic Characteristics of Two Geothermal Systems at the Nanpu Sag, Northern Bohai Bay Basin

The utilization of geothermal energy has gradually increased in northern China because of its unique advantages as a heating supply. However, the sustainable exploitation of geothermal energy usually requires a comprehensive investigation of the geothermal water circulation pattern prevailing at a proposed site. During the exploitation of geothermal energy resources at Nanpu Sag in northern China, thermal anomalies were found to exist in two adjacent regions: the Caofeidian and the Matouying. To reconcile the anomalies and to examine both the source of recharge water and the geothermal systems’ circulation dynamics, a comprehensive investigation was performed using multiple chemical and isotopic tracers (δ2H, δ18O, 87Sr/86Sr, δ13C, and 14C). The total dissolved solids (TDS) of the geothermal water are approximately 750 mg/L and 1,250 mg/L, respectively. The geothermal water isotopes at the two sites are also different, with average values of -9.3‰ and -8.2‰ for δ18O and -73.4‰ and -71‰ for δ2H, respectively. Moreover, the 87Sr/86Sr ratio of geothermal water at Matouying is 0.7185, which is much greater than that of Caofeidian, with an average value of 0.7088. All the results confirm the difference between the two geothermal systems and may explain the two circulation patterns of deep groundwater at Caofeidian and Matouying. The reservoir temperature obtained from theoretical chemical geothermometers is estimated to be 83–92°C at the Caofeidian and 107–137°C at the Matouying, respectively. The corrected 14C age implies a low circulation rate that would allow sufficient time to heat the water at Caofeidian. In addition, we propose a geothermal conceptual model in our study area. This model could provide key information regarding the geothermal sustainable exploitation and the effective management of geothermal resources.

Development of the four-dimensional lattice spring model for thermo-mechanical fracturing and large deformation of solids

Thermo-mechanical coupling is a key issue in the fields of engineering structure security, geothermal energy exploitation, metal hot working, crustal evolution, etc. This work aims to further develop the four-dimensional lattice spring model (4D-LSM) to address thermo-mechanical coupling problems involving fracturing and large deformations. To reproduce the thermal governing equations, a thermal pipe network partially or completely duplicates the corresponding mechanical lattice, where Fourier's law is solved at the pipe level. Furthermore, two different time steps are adopted in the calculations of the equations of force and heat to enable the coupled model to address both transient and steady-state thermo-mechanical coupling problems. The influence of the thermal field on the mechanical responses is addressed through the thermal expansion equation, and the influence of fracturing and recontacting on the thermal connections of the pipe is considered. By introducing thermal damage functions, the influence of temperature on material properties has been considered in the coupled model. A series of examples are evaluated to verify the correctness and accuracy of the coupled thermo-mechanical 4D-LSM. Next, several application examples are analysed to show the ability of the coupled model to simulate the thermal fracturing of heterogeneous materials and the large deformation behaviours of solids.

Magnetically inferred regional heat flow and geological structures in parts of Chad Basin, Nigeria and their implications for geothermal and hydrocarbon prospects

This study analysed high-resolution aeromagnetic data over part of Chad Basin, Nigeria to determine the implications of geological structures and heat flow on the geothermal and hydrocarbon potential of the basin. Curie Point Depth (CPD) analysis, Curvature analysis and Source Parameter Imaging (SPI) were applied in this study. The estimated CPD and heat flow range from 11to19km and from 75to125mW/m2 respectively. The geological structures in the area predominantly trend in the E-W direction, followed by the ENE-WSW direction. Other prominent structural trends include NE-SW and WNW-ESE. The depths to the magnetic sources range from about 0.1 km to over 5 km. A large number of shallow-seated magnetic structures, believed to be intra-sedimentary intrusive bodies, were mapped in the southern and northwestern parts of the study area. The estimated heat flow in Chungul Buturi and Gumsa areas was found to be sufficient for the economic exploitation of geothermal energy. The results of this study showed that the basin is thermally matured for hydrocarbon generation. However, high magnitudes of heat flow and the presence of a large number of intrusive bodies in parts of the basin might have been the reason behind the unsuccessful attempts to find hydrocarbon in commercial quantities in the basin. The results also showed that the basin has a higher potential for gas accumulation than oil. Future exploration for commercial hydrocarbon accumulation in the basin may be successful if the exploration sites are narrowed down to the regions where moderate heat flow, high sedimentary thicknesses with few shallow seated magnetic sources (intrusives), and elongated geological structures were mapped in this study.

A Monte Carlo based approach to the resource assessment of Jamaica's geothermal energy potential.

The Eastern Caribbean chain of islands is commonly known to exhibit high-enthalpy systems for geothermal energy exploitation. The northernmost Caribbean Community member state of Jamaica possesses physical manifestations of 12 hot springs across the island. Previous investigations indicate that of the potential 12 hot springs, Bath, Windsor and Milk River springs have cogent geothermometry of their thermal fluids with estimated temperature ranges of (80-102°C), (128-156°C), and (158-206°C), respectively. The paper provides numerical findings for each geothermal system of interest and performs Monte Carlo simulations to optimize calculated findings. The determined quantitative findings are considered under the context of environmental savings and policy regime conditions for driving geothermal energy development. The three areas of interest are situated within the Rio Minho Basin, the Dry Harbour Mountains and the Blue Mountain South Basin. Through the consideration of a 25-year lifetime for production, a collective total of 94.81 MWe of geothermal power reserves can be absorbed into the national energy mix, displacing an estimated 0.38 million barrels of oil imports, resulting in approximately 0.44 million tonnes of carbon dioxide emissions being avoided per year. This article is part of the theme issue 'Developing resilient energy systems'.

A laboratory study on fracture initiation and propagation of granite under cyclic-injection hydraulic fracturing

The abundant geothermal energy in hot dry rock (HDR) geothermal reservoirs is an attractive renewable energy resource with great potential. Cyclic injection in hydraulic fracturing has been proved to be a suitable way for the geothermal energy exploitation. However, the fracture initiation and propagation regimes induced by cyclic injection have been inadequately studied, and the fracturing optimization for HDR is often by experience. For this reason, true tri-axial hydraulic-fracturing tests were conducted to study the initiation and propagation of hydraulic fractures, while the specimens were subjected to the cyclic injection with different cycle time duration and injection rate. The results revealed that the initiation of hydraulic fracture was displayed as three basic patterns, and these fracture-initiation patterns were developed into two fracture geometries: simple fracture with only 2–4 strands and complex fracture network with >4 strands. The main reason for this difference is that the initiation and propagation of hydraulic fracture is controlled by the way of fluid circulation, and the cycle time duration and injection rate each played a different role in hydraulic fracturing. At a low injection rate, the initiation and propagation of hydraulic fractures under the high-frequency cycle (cycle time duration = 10 and 20 s) are mainly controlled by the change of injection pressure. Here, the hydraulic energy mainly acts on the rock near the well. The frequent change of injection pressure promotes the initiation of micro-fractures and forms a complex but short hydraulic fracture network. However, when high injection rate is subjected, too high and too low cycle frequencies (cycle time duration = 5 and 40 s) both tend to form a simple fracture, but the fracture has strong extension ability. With that, the similarity criterion of physical phenomena between the on-site prototype and the experimental model were discussed, and these lab-scale results were translated into the fracturing site of HDR.

Site characterization for a study on shallow geothermal energy exploitation in Southern Brazil

The energy crisis scenario currently going on in Brazil, along with the need to reduce greenhouse emissions, lead to an urgent need to design buildings with greater energy efficiency. Shallow geothermal energy surges as a sustainable alternative to reduce the electricity consumption in buildings related to air conditioning and water heating systems. In Brazil, the use of this technique is still incipient due to the lack of studies that demonstrate its viability in the country’s climatic conditions, as well as underground temperature and demand for acclimatization of buildings. The aim of the current work is to present a site characterization for the first geothermal energy investigation carried out in the Brazilian South region. This study is being conducted at the Geotechnical Experimental Site of the State University of Ponta Grossa, and this paper describes the physical, mineralogical, thermal and mechanical characteristics of this site, which comprises a thick layer of a lateritic sandy clay soil over a silty sand layer. The preliminary results of the ground temperatures are consistent with the common trends reported in the literature, showing more expressive oscillations near the ground surface, and becoming approximately constant at higher depths.

Experimental quantification of the evolution of the static mechanical properties of tight sedimentary rocks during increasing-amplitude load and unload cycling

Understanding the linearly and nonlinearly elastic behaviors of tight reservoir rocks is crucial for numerous geophysical and geomechanical applications in hydrocarbon exploration and production, geologic repositories for greenhouse gases, and geothermal energy exploitation. We have performed a suite of triaxial load and unload cycling tests with increasing stress amplitudes on three tight sedimentary rocks to explore the evolution of their static mechanical properties (Young’s modulus and Poisson’s ratio). We intend to depict the transition from linear to nonlinear elasticity by combining static measurements with dynamic measurements. The experimental results suggest that static mechanical properties increase upon load stress cycling, but they decrease upon unload stress cycling. Upon the increasing-amplitude unload cycling, static mechanical properties gradually decrease from values approaching dynamic properties to values closer to static properties upon load cycling. By quadratically fitting the static mechanical properties as functions of the strain amplitude in the process of unload cycling, we define a characteristic strain amplitude of approximately 5 × 10−5 to distinguish the linearly elasticity-dominated and nonlinearly elasticity-dominated behaviors for three tight rocks. Such transitional behavior in tight sedimentary rocks can be microscopically explained by the gradual activation of friction-controlled sliding from the beginning of the cyclic stress unload. These observations provide direct experimental evidence of the transition from linear to nonlinear elasticity for tight sedimentary rocks during the laboratory static measurements, which will facilitate understanding of the dynamic-static parameter correlation and the modeling of rock deformations in geoscience or geoengineering applications.

Geothermal Energy Exploitation and Power Generation via a Single Vertical Well Combined with Hydraulic Fracturing

AbstractA method of single vertical well combined with hydraulic fracturing is proposed to prevent short circuits and enhance heat mining. The technical and economic feasibilities of geothermal ene...

An Hourly Optimization Approach for the Design of Borehole Heat Exchangers for the Exploitation of Shallow Geothermal Energy

An Hourly Optimization Approach for the Design of Borehole Heat Exchangers for the Exploitation of Shallow Geothermal Energy

Bacterial diversity, physicochemical and geothermometry of South Asian hot springs.

Extreme ecosystems with enormous arrays of physicochemical or biological physiognomies serve as an important indicator of various processes occurred and/or occurring in and on the Earth. Among extreme habitats, hot springs represent geothermal features which are complex systems with a well-defined plumbing system. Besides geological tectonic based hypsography and orology annotations, the hot springs have served as hot spots for ages where there is an amalgamation of nature, religion, faith, health, and science. Thus, there remains an escalating scope to study these hot springs all over the world. The Himalayan Geothermal Belt (HGB) banquets three densely demographic countries i.e. Pakistan, India and China, that hosts numerous hot springs. Studies on the hot springs distributed over these countries reveal Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria as the predominant bacterial phyla. The bacterial diversity shows a significant positive correlation with physicochemical parameters like temperature, pH, Na+, HCO3 -, etc. Physicochemical analyses of these hot springs indicate the water mainly as Na-Cl, Na-HCO3, SO4-Cl, and mixed type, with temperature ranging approximately between 100-250°C as predicted by various geothermometers. Numerous studies although done, not much of a comprehensive database of the analysis are provided on the hot springs harboured by the HGB. This review aims to give a cumulative illustration on comparative facets of various characteristic features of hot springs distributed over the HGB. These are found to be of great importance with respect to the exploitation of geothermal energy and microflora in various sectors of industries and biotechnology. They are also important sources in terms of socio-economic perspective, and routes to eco-medical tourism.

Analysis of the Geothermal Energy Utilization of Mine Water from Rožná I Mine, Czech Republic

The paper presents an analysis focused on the possibility of using geothermal energy from the Rožná I Uranium Mine through mine water as a heat source. The Rožná I Uranium Mine makes part of the Rožná deposit, whose rock mass cannot be considered homogeneous in terms of geothermal energy utilization, but heterogeneous, where there are positive and negative influences, the so-called geo-factors of geothermal energy utilization. The possibility of geothermal energy exploitation was assessed based on available materials and background information. The main parameters are the thermal conductivity coefficients of the rock mass, the ground heat flux of the area, the geothermal degree or its inverse value, the geothermal gradient. The exploitability of the geothermal potential of the mine water was determined using several calculations. This availability was assessed both in terms of the maximum achievable thermal output in combination with a heat pump and the long-term sustainability of this output. Keywords: Geothermal energy; Heat pump; Mine water; Rožná.

Experimental Study of the Heat-Transfer Performance of an Extra-Long Gravity-Assisted Heat Pipe Aiming at Geothermal Heat Exploitation

The installation and operation of enhanced geothermal systems (EGS) involves many challenges. These challenges include the high cost and high risk associated with the investment capital, potential large working-fluid leakage, corrosion of equipment, and subsiding land. A super-long heat pipe can be used for geothermal exploitation to avoid these problems. In this paper, a high aspect-ratio heat pipe (30 m long, 17 mm in inner diameter) is installed vertically. Experiments are then carried out to study its heat-transfer performance and characteristics using several filling ratios of deionized water, different heating powers, and various cooling-water flowrates. The results show that the optimal filling-ratio is about 40% of the volume of the vaporizing section of the heat pipe. Compared with a conventional short heat pipe, the extra-long heat pipe experiences significant thermal vibration. The oscillation frequency depends on the heating power and working-fluid filling ratio. With increasing cooling-water flow rate, the heat-transfer rate of the heat pipe increases before it reaches a plateau. In addition, we investigate the heat-transfer performance of the heat pipe for an extreme working-fluid filling ratio; the results indicate that the lower part of the heat pipe is filled with vapor, which reduces the heat-transfer to the top part. Based on the experimental data, guidelines for designing a heat pipe that can be really used for the exploitation of earth-deep geothermal energy are analyzed.

Closed-Loop Systems for Geothermal Energy Exploitation from Hydrocarbon Wells: An Italian Case Study

Geothermal energy resources associated with disused hydrocarbon wells in Italian oilfields represent a considerable source of renewable energy. Using the information available on Italian hydrocarbon wells and on-field temperatures, two simplified closed-loop-type systems models were implemented in the Python environment and applied to a selected hydrocarbon well (Trecate4) located inside the Italian Villafortuna–Trecate field (Northwestern Italy). Considering the maximum extracted working fluid temperatures, Coaxial WBHE turned out to be a better performing technology than the U-tube version. The obtained outflow temperatures of the working fluid at the wellhead for Coaxial and U-tube WBHEs of 98.6 °C and 84 °C, respectively, are both potentially exploitable for ensuring a multi-variant and comprehensive use of the resource through its application in sectors such as the food industry, horticultural and flower fields.

Particle migration and formation damage during geothermal exploitation from weakly consolidated sandstone reservoirs via water and CO2 recycling

Coupled migration and retention of suspended injection particles and reservoir particles can severely damage the formation, especially for weakly consolidated sandstone geothermal reservoirs. Understanding their migration and retention is significant to prevent undesired formation damage. The forces acted on these particles were calculated, and then a comprehensive simulation model was established to analyze the coupled particle migration and retention. Massive detachment of reservoir particles, formation of wormhole-like preferential flow paths, and retention of the injected suspended particles are identified as three successive stages during geothermal energy exploitation via water recycling. The mobile reservoir particles play a leading role in the first two stages, while the injected suspended particles mainly affect the last stage. Sensitivity analysis indicates that the high injection-production pressure difference and low concentration of injected suspended particles are conducive to form preferential flow paths, but a severe local reservoir blockage may occur under high mobile reservoir particles. CO2 can effectively reduce reservoir damage caused by particle migration due to its high mobility and low drag force. Although the region of reservoir particle detachment is large during geothermal energy exploitation via CO2 recycling, more preferential flow paths can form to reduce the formation blockage caused by particle migration.

Sustainability of Shallow Geothermal Energy for Building Air-Conditioning

Geothermal heat pumps have a widespread diffusion as they are able to deliver relatively higher energy output than other systems for building air-conditioning. The exploitation of low-enthalpy geothermal energy, however, presents crucial sustainability issues. This review investigates the primary forms of the environmental impact of geothermal heat pumps and the strategies for their mitigation. As life-cycle analyses shows that the highest impacts arise from installation and operation stages, most optimization studies focus on system thermodynamics, aiming at maximizing the energy performance via the optimization in the design of the different components interacting with the ground and serviced building. There are environmental studies of great relevance that investigate how the climate and ground properties affect the system sustainability and map the most suitable location for geothermal exploitation. Based on this review, ground-source heat pumps are a promising technology for the decarbonization of the building sector. However, a sustainable design of such systems is more complex than conventional air-conditioning systems, and it needs a holistic and multi-disciplinary approach to include the broad environmental boundaries to fully understand the environmental consequences of their operation.

A theoretical thermal conductivity model for soils treated with microbially induced calcite precipitation (MICP)

Soil thermal conductivity is a predominant factor affecting the efficiency of exploitation of geothermal energy. Microbially induced calcite precipitation (MICP) technology has been proved to be effective in improving soil thermal conductivity. However, there is still a lack of a thermal conductivity prediction model for MICP treated soils. In this study, a theoretical thermal conductivity prediction model was developed based on the heat conduction theory and a simplified 2D geometric soil unit. The performance of this model was evaluated using the measured thermal conductivity in published literature. The results show that the predicted soil thermal conductivity agrees with the measured values well, especially, when the soil saturation (water content of the soil) is greater than 0.1. We analyze the influencing factors of soil thermal conductivity after MICP treatment on micro-scale. The results show that the soil thermal conductivity increases nonlinearly with the ratio of cement radius to soil particle radius, β. For example, the thermal conductivity can be increased by more than 16 times from 0.25 W/(m K) to 4.14 W/(m K) when β increases from 0 is 0.8, if the ratio of soil particle spacing to soil particle radius ξ is zero. ξ is also found to have a significant influence on soil thermal conductivity. For example, the soil thermal conductivity increases by 0.19 W/(m K) and 1.08 W/(m K) in dry and saturated states, respectively, when ξ increases from 0 to 0.33. This theoretical thermal conductivity model will provide a great calculation method for the soil thermal conductivity after MICP treatment.

A review of the status of organic pollutants in geothermal waters

Studies on organic pollutants in geothermal environments have received little attention; hence this review is necessary. The presence of trace organic pollutants such as benzene and xylenes has been reported as some of the main sources of pollution in geothermal systems. Previous studies using quantitative fluid inclusion gas analysis, Fischer–Tropsch Type (FTT) experiments and Gas chromatography-Mass spectrometry (GC-MS) have shown that there is a considerable presence of organic pollutants such as trace mono aromatic hydrocarbons (MAHs), polycyclic aromatic hydrocarbons (PAHs), and emerging organic contaminants whose origin is both biogenic and abiogenic. Organic pollutants were initially not considered in geothermal development and utilization despite the fact that these toxic chemicals can precipitate severe ecological poisoning and potential risks to human health and aquatic life in a given geothermal environment, even at very low concentrations. The significant presence of benzene in various geothermal systems is of concern because it is a precursor for many aromatic compounds that are bio-accumulative and toxic to water regimes and the environment. Thermophilic and mesophilic bacteria, nonetheless, play a critical role during the biodegradation of organic pollutants in geothermal regimes. From the findings of this review, it is difficult to classify geothermal energy exploitation and utilization as an environmentally benign resource.