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Considering the abundance of renewable energy potential in Turkey, green hydrogen derived from renewable sources holds great promise as a fuel. This paper presents a model for obtaining green hydrogen from medium-temperature geothermal sources. In this model, the Zilan location in the Van province of Turkey was identified as a suitable site for electricity and hydrogen production from low or medium-temperature geothermal sources due to its significant geothermal and water resource potential. In this regard, the installed capacity of the Organic Rankine Cycle (ORC) geothermal power plant is determined by using Monte Carlo Simulation based on the characteristics of the geothermal well at this location, and subsequently, the hydrogen production performance has been evaluated by analyzing the water of Lake Van. According to the analysis results, Lake Van was found to be efficient for hydrogen production. Hydrogen production from Lake Van water was subsequently simulated using the electrolysis method with this ORC geothermal power plant. According to the findings of this model, the hourly hydrogen production potential at this location using a 1.4 MW ORC plant, based on 2022 data, was estimated to be 18.6 kg, which is projected to increase to 28 kg based on 2050 estimated data. In addition, the techno-economic analysis of this compact green hydrogen production process was conducted in the study. The production cost of 1 kg of hydrogen was calculated to be €4.91 in 2022, while it is expected to be €1.21 in 2050. These results indicate that ORC technology will become competitive in hydrogen production in the upcoming years. • Determining the installed capacity of an ORC plant using Monte Carlo simulation. • Producing green hydrogen through an ORC power plant. • Analysis of the hydrogen production potential of the relevant water source. • Selection of the suitable electrolysis unit. • Hourly hydrogen production capacity of compact facility. [ABSTRACT FROM AUTHOR]

The Hellisheidi geothermal power plant, located in Iceland, is a combined heat and power double-flash geothermal plant with an installed capacity of 303.3 MW of electricity and 133 MW of hot water. This study aimed to elucidate the environmental impacts of the electricity and heat production from this double-flash geothermal power plant. In this vein, firstly, the most updated inventory of the plant was generated, and secondly, a life-cycle assessment approach based on the exergy allocation factor was carried out instead of applying the traditionally used allocations in terms of mass and energy. The functional unit was defined as the production of 1 kWh of electricity and 1 kWh of hot water for district heating. The life-cycle stages included the (i) construction, (ii) operation (including abatement operations and maintenance), and (iii) well closure of the geothermal plant. All of the life-cycle stages from construction to dismantling were considered. Finally, the results on the partitioning of the environmental impact to electricity and heat with exergy allocations showed that most of the impact should be charged to electricity, as expected. Furthermore, the distribution of the environmental impacts among the life-cycle stages determined that the construction stage was the most impactful for the electricity and heat production. This result was attributable to the large consumption of steel that was demanded during the construction of the geothermal power plant (geothermal wells, equipment, and buildings). Impacts due to the abatement stage demonstrated that this stage satisfactorily reduced the total impact attributed to the three life-cycle stages of the geothermal power plant. [ABSTRACT FROM AUTHOR]

Recently, the development and exploitation of renewables-driven multigeneration systems can be a sensible solution to reduce the limitations of fossil energies and their negative environmental impacts. The combination of two geothermal and solar energies, in addition to reducing the installation costs of solar systems, can support the efficiency improvement of the geothermal-driven energy systems. In addition, the use of suitable downstream cycles in such energy conversion processes can improve thermodynamic and economic performances. The coefficient of performance offered by a generator absorber heat exchanger-based refrigeration cycle can be higher than that by the ejector and absorption refrigeration processes. A comprehensive thermodynamic-conceptual and exergoeconomic evaluations as well as two-objective optimization on a new geothermal-driven multigeneration system, based Sabalan geothermal wells, has been developed in this paper. The proposed system is able to produce power, heating, cooling, and hydrogen fuel. In the developed configuration the geothermal source is considered as the main source of energy production and a linear Fresnel reflector-based solar unit produces a portion of the required thermal power of the system. Further, a single-flash cycle, a water electrolysis unit (based on alkaline electrolyzer cell), and a generator absorber heat exchanger unit are embedded to generate various forms of energy. The overall outcomes indicated that the proposed system can produce 4.1 MW of electric power, 1.67 MW of heating load and 1.46 MW of cooling load. In addition, the hydrogen production rate of the energy process is equal to 5.75 kg/h. In such a context, the considered process can achieve energy and exergy efficiencies of almost 34.2% and 66.3%, respectively. Based on the optimization findings, the energy efficiency can be improved by approximately 9.75% according to the optimal input data. Additionally, the total product unit cost rate can be reduced by almost 4.3% at the same time. Relying on a parametric analysis, variables affecting the performance of the considered system are identified. The conceptual design of the solar unit is also presented regarding the geographical and climatic data of the desired region. [ABSTRACT FROM AUTHOR]

Distributed Acoustic Sensing (DAS) is an emerging technology for acquiring seismic data on virtual sensors densely distributed along an optical fiber. The broadband response of the sensors, associated with the possibility of deploying fiber optic cables in harsh conditions and the relatively moderate cost of this sensing element gives clear perspectives for DAS in geothermal wells to contribute to the monitoring operations of geothermal plants. However, the technical feasibility of managing the large flow of data generated by the DAS and the suitability of the strain-rate acquisitions to monitor locally induced seismicity was yet to be assessed. We propose a monitoring concept establishing DAS as an effective component of the seismic monitoring of the Schäftlarnstraße geothermal plant (Munich, Germany). The underlying data management system links the existing on-site infrastructure, including the fiber optic cable deployed in one of the site's injection wells and the associated DAS recorder, to a cloud Internet-of-Things (IoT) platform designed to deliver both a secure storage environment for the DAS acquisitions and optimized computing resources for their processing. The proposed solution was tested over a period of six months and showed the feasibility of efficiently acquiring and processing the large flow of continuous DAS data. For seismic risk mitigation purposes, we additionally investigate the potential of the monitoring concept to tend towards real-time monitoring. The processing outcomes, focusing especially on two detected local seismic events, demonstrates the relevance of DAS from geothermal wells for the (micro)seismic monitoring of the geothermal site. Despite the noisy operational conditions, the applied processing workflow takes advantage of the sensors' high spatial density for data denoising and event triggering and highlights that higher detection sensitivity than conventional seismometers can be achieved. From a different perspective, further analyses of the DAS records confirm the logging capabilities of the technology, especially regarding well completion integrity. The 6-months test period shows that permanent DAS can be integrated as a routine seismic monitoring component of geothermal plants and advantageously complement surface seismometer based networks, especially in urban environments. [ABSTRACT FROM AUTHOR]

In this paper, the 4E assessment (Energetic, Exergetic, Exergoeconomic and Exergoenvironmental) of a low-temperature ORC activated by two different alternatives is presented. The first alternative (S1) contemplates the activation of the ORC through the recovery of waste heat from a flash–binary geothermal power plant. The second alternative (S2) contemplates the activation of the ORC using direct heat from a geothermal well. For both alternatives, the energetic and exergetic models were established. At the same time, the economic and environmental impact models were developed. Finally, based on the combination of the exergy concepts and the economic and ecological indicators, the exergoeconomic and exergoenvironmental performances of the ORC were obtained. The results show higher economic, exergoeconomic and exergoenvironmental profitability for S1. Besides, for the alternative S1, the ORC cycle has an acceptable economic profitability for a net power of 358.4 kW at a temperature of 110 °C, while for S2, this profitability starts being attractive for a power 2.65 times greater than S1 and with a temperature higher than 135 °C. In conclusion, the above represents an area of opportunity and a considerable advantage for the implementation of the ORC in the recovery of waste heat from flash–binary geothermal power plants. [ABSTRACT FROM AUTHOR]

As global efforts intensify to mitigate climate change through Net-Zero by 2050, the transition from fossil fuels to renewable energy sources is of utmost importance. Within this context, geothermal power generation is an underestimated yet rapidly developing field with immense potential. A notable opportunity arises from repurposing abandoned oil and gas wells (AOGWs) as alternative sources for geothermal power production. This study employs multi-criteria decision analysis (MCDA) to examine the techno-sustainability of four geothermal power systems: i) a business-as-usual geothermal power plant (GEO bau), ii) repurpose two completely AOGWs for geothermal power generation (R-GEO double), iii) repurpose a single completely AOGW (R-GEO single), iv) repurpose semi-AOGWs (i.e., wells still in operation but with high water cut, R-GEO semi). We assessed 30 criteria across technical, environmental, economic, and social dimensions via the analytical hierarchy process. The study identifies R-GEO semi as the most techno-sustainable option due to its superior performance across environmental, economic, and social dimensions. However, GEO bau closely follows R-GEO semi , securing its position as the second-best option, marked by its outstanding technical proficiency and robust environmental and social performance. Conversely, R-GEO double and R-GEO single show limited techno-sustainability competitiveness. When sensitivity analyses are applied to the weighting factors, R-GEO semi demonstrates resilience and remains as the best option in most cases. However, GEO bau could outperform R-GEO semi when the value of technical criteria is increased (weightings >0.255) or when the weightings for environmental or economic aspects decrease (weightings <0.236 and < 0.244 respectively). R-GEO double and R-GEO single only overtake GEO bau when the economic aspect reaches a weighting of 0.659 or more. Despite R-GEO semi being the most promising option, it faces challenges due to limited power generation capacity and the availability of wells approaching their end-of-lives. The findings underline the necessity for broader stakeholder input, inclusion of more technical and social criteria, and data-driven decision-making processes. • First multi-criteria decision analysis of repurposing abandoned wells for geothermal power. • Repurposed semi-abandoned oil & gas wells are the most techno-sustainable option. • Technical criteria can tilt performance favour towards non-repurposed systems. • Drilling activity should be minimised to boost the deployment of repurposed systems. • Repurposed systems excel when economic criteria are prioritised. [ABSTRACT FROM AUTHOR]

Fengshun geothermal field is the first medium low temperature geothermal field to exploit geothermal energy for electricity generation in China. Due to poor economy and low efficiency, the geothermal power plant was forced to shut down in 2016. In this work, based on the geological data of the well ZK11, we proposed a new heat exploitation scheme with five vertical wells and a binary system, computed the power generation potential and efficiency, and analyzed the main factors influencing heat production. The results indicate that through the five vertical wells, the system attains an electrical power of 1.49–1.05 MW, a reservoir impedance of 0.23–0.29 MPa/(kg/s), a pump power of 0.30–0.49 MW, and an electrical energy efficiency of 4.55–2.12. The electric power of unit flow rate is 22.4–31.7 times that of the existing power plant. Thus, this five-vertical-well system has significant development potential for medium low temperature hydrothermal field. The sensitivity analysis indicates that overburden and underburden permeability, water production rate and injection temperature have a significant impact on heat production performance. Increasing the overburden or underburden permeability will significantly reduce reservoir impedance and increase energy efficiency. Reducing the water production rate and injection temperature within a certain range can improve energy efficiency. This work also provides a guideline for the exploitation and power generation of future medium low temperature hydrothermal field in Fengshun and other sites under similar conditions. [ABSTRACT FROM AUTHOR]

Fengshun geothermal field is the first medium low temperature geothermal field to exploit geothermal energy for electricity generation in China. Due to poor economy and low efficiency, the geothermal power plant was forced to shut down in 2016. In this work, based on the geological data of the well ZK11, we proposed a new heat exploitation scheme with five vertical wells and a binary system, computed the power generation potential and efficiency, and analyzed the main factors influencing heat production. The results indicate that through the five vertical wells, the system attains an electrical power of 1.49–1.05 MW, a reservoir impedance of 0.23–0.29 MPa/(kg/s), a pump power of 0.30–0.49 MW, and an electrical energy efficiency of 4.55–2.12. The electric power of unit flow rate is 22.4–31.7 times that of the existing power plant. Thus, this five-vertical-well system has significant development potential for medium low temperature hydrothermal field. The sensitivity analysis indicates that overburden and underburden permeability, water production rate and injection temperature have a significant impact on heat production performance. Increasing the overburden or underburden permeability will significantly reduce reservoir impedance and increase energy efficiency. Reducing the water production rate and injection temperature within a certain range can improve energy efficiency. This work also provides a guideline for the exploitation and power generation of future medium low temperature hydrothermal field in Fengshun and other sites under similar conditions. [ABSTRACT FROM AUTHOR]

This paper reports a comprehensive survey of well drilling time and cost. The models include both specific correlations on various well types and generalised correlations for rough estimation. The models are derived from robust multivariable regression to minimise the residuals. Africa has the highest construction cost component in well drilling and the United States has the lowest. Data in various regions are compared with European and World average drilling data. Drilling time in Italy is similar to Europe and world averages. The proposed model directly estimates both the drilling cost and time to be used in fundamental research and feasibility studies for geothermal power plants applicable worldwide. [ABSTRACT FROM AUTHOR]

Abandoned oil well can be a promising alternative to be retrofitted to extract geothermal energy than the conventional geothermal well. This study investigates the potential of converting abandoned oil well into geothermal energy power plant by combining computational fluid dynamics (CFD) simulation, process simulation, and techno-economic analysis. A detailed CFD model was formulated and validated with verified data from published literature. The model was then utilized to study key performance variables on heat extractions coupled with the Organic Rankine Cycle (ORC) to generate power and its subsequent techno-economic analysis. The results indicate that, due to relatively low temperature profile in typical Malaysian wells, the Levelized Cost of Electricity (LCOE) of the ORC system was found to be almost double than that of conventional geothermal technologies. To reduce the LCOE, at least four abandoned wells in a close proximity are required. Alternatively, other renewable energy sources (e.g., solar, biomass) could be used to upgrade the geothermal well. This techno-economic analysis shall serve as a preliminary assessment on the feasibility of utilizing abandoned oil wells in Malaysia for geothermal energy extraction. • Coupling of CFD and ORC process modeling for geothermal extraction from abandoned oil well. • Techno-economic analysis was conducted for case study in Malaysia. • The levelized cost of electricity (LCOE) is found to be around 6 cent USD per kWh. • Geothermal gradient of the well plays important role on the feasibility of the system. [ABSTRACT FROM AUTHOR]

In this work, a thermodynamic analysis consisting of energy and exergy analyses is carried out to determine the performance of a single flash geothermal power plant. A new derivation for determination of the optimum separator temperature, which results in maximum turbine power output, is achieved. The energy and exergy analyses are carried out at that optimum separator temperature. The thermodynamic derivation showed that the separator would result in maximum performance of the power plant when it operates at the average value of the production well and condenser temperatures. Moreover, the derivation was numerically validated by calculating three different values for the geothermal well temperatures. The results show that the highest exergy destruction rate is in the expansion valve followed by the steam turbine, the mixing process and the pump. The separator has exactly zero exergy destruction rate while the condenser has almost zero exergy destruction rate. The results also show that the exergy destruction rate for all components of the power plant decreases with reduction in the geofluid temperature of the production well except for the condenser. The maximum energy efficiency of the power plant is about 12.5, 11 and 9.5% when the geofluid of the geothermal well temperature is 300, 275 and 250°C, respectively. [ABSTRACT FROM AUTHOR]

This study presents and evaluates the feasibility of a novel hybridization of modified Kalina cycle, reverse osmosis desalination, and low-temperature water electrolysis utilizing geothermal energy to yield power, distilled water, and hydrogen, respectively. The scientific impact of the current work has been improved considering the features of Sabalan flash-binary geothermal wells in Iran as a real model through a case study. In addition to designing a novel setup, the smart use of multi-heat recovery technique, modifying the base cycle, and utilizing a part of generated distilled water to produce hydrogen by the electrolyzer are the other structural originalities, distinguishing the current work from the previous studies. The suggested system is scrutinized via a parametric study and optimized based on a genetic algorithm. The parametric study demonstrated that the highest sensitivity of varying the performance criteria of the whole system is attributed to the change in flash tank pressure. Moreover, the multi-objective optimization led to achieving the exergy efficiency and trigeneration gain output ratio as 51.3% and 1.7 for the system, respectively. Furthermore, the system was able to produce 4795 kW of power, 5.3 kg/h of hydrogen, and 19.9 kg/s of distilled water. • Assessment and optimization of a novel geothermal-based trigeneration system. • Smart use of multi-heat recovery technique to enhance the structural capability. • Considering the features of Sabalan flash-binary geothermal wells for a case study. • Hydrogen production has the most impact on the proposed system's exergy efficiency. • Optimum hydrogen and freshwater generation rates are 5.3 kg/h and 19.9 kg/s, separately. [ABSTRACT FROM AUTHOR]

An innovative Bi-Evaporator Ejector Refrigeration Cycle (BE-ERC) working with different zeotropic mixtures is devised in this study. Next, the proposed BE-ERC system is used as binary cycle of a modified Double-Flash Geothermal Power Plant (DF-GPP) to simultaneously produce cooling and power from the same geothermal well. A comprehensive modeling of the proposed integrated system is carried out from thermodynamics laws viewpoints and the results are elaborated in detail. Based upon the results, the use of R142b/Pentane (0.6/0.4) is highly commendable due to achieving the maximum refrigeration load, Coefficient of Performance (COP), and total energy efficiency of 137.83 kW, 0.329, and 20.37%, respectively. Although net electricity and exergy efficiency were not maximum at this condition, their value was competitive. Accordingly, with the use of R142b/Pentane (0.6/0.4), the net electricity, exergy efficiency of the BE-ERC, and total exergy efficiency were calculated 18.61 kW, 2.16%, and 20.95%, respectively. Among all elements of the integral set-up, the first ejector (the main ejector in the BE-ERC) had the highest exergy destruction of 26.09 kW out of overall fuel exergy of 190.7 kW (13.68%), followed by the vapor generator with exergy destruction of 24.4 kW. • To devise a new BE-ERC and demonstrate its superiority to the existing ones. • To use zeotropic mixture in the devised BE-ERC. • To use the devised BE-ERC in integration with a modified DFB-GPP for cogeneration. [ABSTRACT FROM AUTHOR]

We review the key factors that facilitated the successful development of a geothermal reservoir at Neal Hot Springs (NHS), Oregon, by a private company. The NHS geothermal field development plan, financing tools, and fluid circulation model provide a template for the development time, financing and well rates required to sustain geothermal power generation in similar setups elsewhere. The early economic performance and life-cycle analysis are specified using company data, applying a financial evaluation tool developed by the National Renewable Energy Laboratory (NREL). The Neal Hot Springs geothermal project was enabled by a combination of financing sources: U.S. federal loan guarantee and cash grant, state tax credit and private equity. Flow patterns in the NHS geothermal reservoir are visualized using a novel streamline simulation tool applying known well rates and benchmarking the residence time of re-injected brine based on tracer tests performed by the company. Temperature of produced brine has stayed remarkably constant over the first years of NHS plant operations, which we ascribe to advection of heat by an upwelling far-field flow beneath the plant’s production wells. [ABSTRACT FROM AUTHOR]

In a recent paper we discussed the development of a new transient geothermal wellbore simulator. In the present paper we discuss the application of this simulator to the modelling of challenging and interesting flows that occur in a geothermal wellbore. The first group of problems involve the opening and closing of hot geothermal wells with rapid transient flows. In some cases, this involves counter-flow with steam flowing upwards and liquid water flowing downwards. The final test case in this category is the simulation of a completion test which involves four stages: cold water injection, heating up of a shut-in well, discharge of the well to the atmosphere, connection of the well to a separator. Simulation of well stimulation by air-lifting and air-compression demonstrate the capability of the simulator for modelling flows of air-water mixtures with a moving interface between the phases. Finally, we demonstrate the ability of the simulator to model injection of water-carbon dioxide mixtures, with an increasing proportion of CO 2. This is of particular importance as operators look to carbon sequestration as a way of mitigating green-house gas emissions from geothermal power plants. These are a selection of the more interesting problems of the many test cases that were used during the development of our simulator to ensure that it is robust and can simulate the full range of complex transient flows that can occur in a geothermal well. [ABSTRACT FROM AUTHOR]

Deliverability of geothermal production wells is evaluated by measuring wellhead pressure versus mass flow rate at several wellhead pressures. Controlling a main valve of the well results in the changes in wellhead pressure and mass flow rate. However, duration required for these variables to stabilize depends on flowing behavior of steam-water two-phase fluid in the wellbore. Fluid stabilization seems to be an important parameter, mainly for short period of measurement. In addition, the manner of controlling valve operation whether it starts from the well in full-closed condition or in full-opened condition seems to affect this flow stabilization. Thus, the experiment was carried out for a production well 2H-21 at Hatchobaru geothermal field, Japan to verify these hypotheses. The measurement apparatus consisted of pressure sensors, water level sensor and a PC to store the measured data. The data were recorded every second for the pressures at upstream of the orifices, the pressure drops at the orifices, the pressures at the separators, and the water level at weir box. The degree of valve opening was changed three times during the measurement. Then, the duration of respective wellhead valve operation for controlling flow rate affecting the flow stabilization in wellbore was observed. It was found that quick valve operation caused longer period for stabilization and produced impulse response of flow rate soon after the valve operation stopped. The fluid flow required about 7 min to stabilize for closing valve operation whereas it needed longer than 20 min to reach the stable condition for opening valve operation. After changing the wellhead pressure, the steam flow rate stabilized quickly while the water flow rate showed a gradual change. [ABSTRACT FROM AUTHOR]

Knowledge about the thermal conductivity of rock is essential for accurate design of geothermal plants. Thermal conductivity can be measured in situ, with low precision and coarse spatial resolution, or in a laboratory, where samples are subject to altered conditions and represent only limited sections of the borehole. We have developed and evaluated a new technology involving fast, high-resolution, and high-precision scanning of in-situ thermal conductivity within boreholes. The prototype demonstrated the feasibility of the technology for shallow geothermic wells, with an accuracy of 10%. [ABSTRACT FROM AUTHOR]

• Previous studies have not linked the surface and sub-surface in Olkaria and other geothermal fields worldwide. • The wellbore simulator connected the wellhead, and the reservoir simulated pressure and temperature logs for Olkaria Domes in Olkaria, a liquid-dominated geothermal field. The simulation results enabled the calculation of exergy values at any depth using the pressure and temperature between the reservoir and wellhead. Obtained results of the research used to interpret heat transfer between geothermal reservoir layers and the location of the reservoir. • The study demonstrates the importance of connecting the reservoir and wellhead via a wellbore simulation and exergy profiles. Geothermal is the energy for the future and is eco-friendly. Exergy analysis of geothermal power plants has been referenced based on wellhead and surface environment conditions. Previous studies have not linked the surface and sub-surface in Olkaria and other geothermal fields worldwide. The wellbore simulator connected the wellhead, and the reservoir simulated pressure and temperature logs for Olkaria Domes in Olkaria, a liquid-dominated geothermal field. The simulation results enabled the calculation of exergy values at any depth using the pressure and temperature between the reservoir and wellhead. Obtained results of the research used to interpret heat transfer between geothermal reservoir layers and the location of the reservoir. This study takes the exergy analysis to the source of geothermal brine under saturated conditions. The paper presents exergy profiles of geothermal wells at Olkaria Domes. The field data input parameters were wellhead pressure, mass flow rates of steam and brine, wellbore diameter, and the reservoir depths (deeper/second and shallow). A wellbore model developed in 1988 was used to simulate temperature-pressure profiles. The thermodynamic parameters (temperature and pressure) from the wellbore simulator were input parameters in the Engineers Equation Solver (EES) code to calculate entropy, enthalpy, and specific exergy. The wellbore exergy profiles show estimated feed zone depths of -1000 - (-) 2800 m.a.s.l for two-directional and three vertical wells. The profiles predicted convective and conductive heat transfers points. For wellhead temperatures of between 182 -205°C, the reservoir temperatures from the wellbore simulator are high at 292°C. The formation pressures were between 3,978 to 7,710 kPa. Exergy wellbore simulation of the geothermal reservoir predicted the reservoir and heat transfers in the sub-surface. The study demonstrates the importance of connecting the reservoir and wellhead via a wellbore simulation and exergy profiles. [ABSTRACT FROM AUTHOR]

Concentrating solar power plants can be a good choice for green power generation; nevertheless, this technology has low financial profitability and energy dispatch capacities compared to those based on conventional fossil fuels. On the other side, hybridization of concentrating solar power with geothermal energy is a good option for the erection of large-scale power plants with high dispatch capacity and low investment cost, due to the large potential and geographical coincidence of geothermal resources with high solar irradiation areas. Thus, the main aim of the present paper is to investigate the hourly and annual performances of a new combined solar-geothermal power plant. This layout includes a bottoming binary geothermal power cycle that recovers the waste heat from a topping solar tower thermal power plant to generate power. In this process, both steam and organic turbines produce electrical power. By using this new design, the dispatch capacity and annual thermodynamic performances have been raised by more than 30% compared to the conventional solar tower plant. Furthermore, the increase in geothermal production well temperature will increase the dispatch capacity of this new hybrid plant up to 152 GWh annually, for a temperature of 95 °C. • The design of a new CSP-geothermal plant and its performances have been presented. • The topping layout is based on a solar tower power plant similar to Gemasolar. • The bottoming layout is based on a binary geothermal power plant working with R134a. • The optimization of the mass flow rate of the bottoming plant has been performed. [ABSTRACT FROM AUTHOR]

With the growing interest in geothermal energy as a renewable and sustainable energy source, nowadays engineers and researchers are facing technological and environmental challenges during geothermal wells' operation or energy recovery improvement by optimizing surface installations. One of the major problems encountered is the degassing of geothermal brines which are often loaded with dissolved gases, resulting in technical problems (scale formation, corrosion, reduced process efficiency, etc.) and environmental problems through the possible emission of greenhouse gases (CO2, CH4 and water vapor) into the atmosphere. In this work, a method to predict, from readily available information such as temperature and GLR, the bubble point pressure of geothermal fluids as well as the GHG emission rate depending on the surface conditions is presented. This method is based on an extended version of the Soreide and Whitson model with new parameters optimized on the solubility data of several gases (CO2, CH4, N2, O2 and H2) in brine (NaCl + CaCl2 + KCl). The developed approach has been successfully used for the prediction of water content of different gases and their solubilities in different types of brines over a wide temperature and pressure range, and has been applied for the prediction of bubble point pressure and GHG emissions by comparing the results with available industrial data of geothermal power plants including the Upper Rhine Graben sites. [ABSTRACT FROM AUTHOR]

There have been many reports on laboratory experiments measuring TEG (thermoelectric generator) power output at different flow rates of water, different temperatures, and other different conditions, but there have been few field tests utilizing geothermal wells. To this end, we designed a geothermal-TEG apparatus that has a six-layer modularized design to allow expanded power production by increasing the number of layers. After demonstrating the TEG's performance in the laboratory, we tested the apparatus in the field at a well located in the Bottle Rock geothermal field in The Geysers, CA, USA. The whole six-layer TEG device could generate about 500 W electricity with a temperature difference of about 152 °C between the hot and cold fluid manifolds, while each individual TEG chip could generate about 3.9 W. The steam pressure at the inlet of the TEG apparatus was about 122 psi, close to the wellhead pressure of 125 psi. After optimizing the field infrastructure, the TEG device could generate electricity without any leak at the wellhead pressure of 125 psi and the temperature over 176 °C (349 °F). The field test of the six-layer TEG device at Bottle Rock geothermal power plant was considered successful, and plans have begun to design and build a TEG device that could produce power up to 20 kW. • Designed a novel modularized TEG apparatus to allow expanded power production. • Reported an unusual application of TEGs and conducted a field test successfully. • The total power output of the TEG device was more than 500 W at a ΔT of 152 °C. • The voltage and power output of each layer of the TEG device was almost the same. • The field test data of the TEG device followed the trend of the laboratory data. [ABSTRACT FROM AUTHOR]

• Heat mining form deep hot dry rock beneath the current oilfield at bongor basin, chad. • Utilizing carbon dioxide from diesel power plants into deep geothermal reservoirs for heat mining and CO 2 sequestration. • Utilizing oilfield geothermal water from high water-cut oil wells into geothermal wells for heat mining. • Using infrastructures and facilities of oilfield reduces the cost of geothermal project implementation. In this paper, the feasibility of power generation from an enhanced geothermal system (EGS) located beneath an oilfield at the Bongor basin in Chad was examined through the analysis of numerical simulation parameters. A 3D geometric model is constructed to represent the proposed EGS and a thermo-hydro-mechanical (THM) coupled mathematical model was used in the simulation process to link all inter-dependent parameters of heat mining. Oilfield warm water is anticipated to be the circulating fluid of the thermal reservoir due to its ready availability from high water-cut oil wells. Chad depends heavily on a diesel power plant, thus this work further proposes the utilization of carbon dioxide (CO 2) from the power plants to be used as heat mining fluid and likely CO 2 sequestration into deep granite formation. The results indicate that the implementation of EGS beneath the current oilfield would have significant advantages both technically, environmentally, and economically. Oilfield produced water at warm temperatures improved heat mining efficiency and utilization of oilfield water in geothermal wells will reduce costs involved in water treatment and disposal. The geothermal gradient is sufficient to produce water at a higher temperature that can be utilized commercially by different binary power plants. Utilizing CO 2 as heat extraction fluid showed significant heat extraction, higher than using oilfield produced water. Furthermore, substantial amount of CO 2 can be deposited into the formation, thus reducing emission of greenhouse gasses to the atmosphere. [ABSTRACT FROM AUTHOR]

• Geothermal Power. • Ischia. • Geothermal Wells. • Binary Plants. • Hot Water Utilization. Many articles have been published on the pioneering activity carried out in Larderello for the exploitation of the geothermal resources present there. Little is known, however, of the equally pioneering activities carried out in Italy around 500 km south of Larderello for the exploitation of the warm waters found on the Ischia island in front of the Gulf of Naples. With this article we want to analyze the technological evolution that since the 1930s has made it possible to produce electricity from hot water. There are many factors that have made this pioneering development possible. The first one is linked to the geological conditions present on the island, the second one concerns the evolution of the drilling activity which has made available more and more hot water and then steam. The third is linked to the presence, at the engineering faculty of the "Federico II" University of Naples, of creative minds who have designed and made possible the realization of prototypes of binary fluid systems. Starting from a small size of 10 CV (1 CV = 0,98631 HP) working with pure fluids, reaching a size of 300 kW working with immiscible fluids mixtures. In this way they have anticipated the future development of this technology. The article analyzes all these factors to describe the birth, development and decline of this unique experience from which valid lessons can be drawn even in our day. [ABSTRACT FROM AUTHOR]

• Steel well casings used as electrodes in a resistance study. • Low resistance measured at Reykjanes due to high salinity of geothermal fluid. • Electric current travels between casings through brine-filled fractures. • Casings transfer electric current deeper into the ground than surface electrodes. Successful drilling of geothermal wells into fractured hot rock through which geothermal fluid flows is critical to ensure efficient operation of geothermal power plants. This study focuses on investigating a casing-to-casing resistance method for estimating fracture connectivity between wells at Reykjanes geothermal reservoir in Iceland to better understand the fluid-flow in the reservoir. Conductive well casings were successfully used as electrodes to transfer the electric current deeper into the fractured reservoir in an electrical resistance survey. The low resistance measured between wells implies that the wells are connected to the main production zone at Reykjanes and that the current is travelling through fractures filled with conductive geothermal brine from one well casing to another rather than going through a less conductive rock. The measured resistance is compared to an analytical study showing the promising potential the casing-to-casing resistance method has for gaining valuable information about the fracture connectivity in geothermal reservoirs. [ABSTRACT FROM AUTHOR]

• Thermal, hydraulic and geochemical properties are assessed in a geothermal system. • High thermal conductivity formations are analyzed for thermal anomalies. • Potential power production is calculated. • The potential for lithium production is considered. Low-temperature geothermal power plants have great potential to provide baseload electricity worldwide. However, the technology is new and untested, and the systems require a significant financial investment. Site-specific feasibility studies are required to draw together available data and inform developers of production potential and challenges. This study applies coupled thermal, hydraulic, and geochemical modeling to characterize a horizontal geothermal well system in the Williston Basin. This study targeted thermal anomalies overlying 370 m thick halite and dolomite formations from the Devonian period. The halite and dolomite produced a 6°C thermal anomaly, or 16°C km−1 increase in the thermal gradient. A >5.0 MW power plant was achieved when targeting the Dawson Bay formation. A fractured, horizontal well in the Bakken formation was re-entered for injection, providing a savings of up to 40% of drilling costs. The geochemical analysis allowed for the calculation of potential precipitates in the production casing, and consideration of mitigation methods. In addition, the co-production of lithium was identified as potentially profitable in the Dawson Bay Formation. Considering the available resources and assets provided unique data to inform the development of a geothermal system in the Williston Basin. [ABSTRACT FROM AUTHOR]

The UK is rich in heat-producing granites, especially in the county of Cornwall, suggesting the potential for energy production with low environmental footprint. The United Downs Deep Geothermal Power (UDDGP) project aims to demonstrate the technical and commercial viability to produce electricity from the Cornish geothermal resource, exploiting the natural permeability of a significant deep structural fracture zone known as the Porthtowan Fault Zone. Drilling of the first well started at the end of 2018, and the plant is expected to be operational by mid-2020. A relevant question is whether deep geothermal energy is truly environmentally benign. This article presents a comprehensive and detailed Life Cycle Assessment study that i) identifies the main life-cycle sources of environmental impacts for the production of electricity in the UDDGP plant; ii) investigates the effects on the environmental impacts of significant uncertainties surrounding the project, such as availability of geothermal fluid and configuration of the power plant, and iii) compares the performance of the UDDGP operation, and by extension of the putative geothermal energy production in the UK, with other key energy sources in the country. The life cycle inventory relies on a combination of site-specific data for wells construction and literature data for above-surface facilities and stimulation techniques. We validated our model by comparing climate change impacts of UDDGP with those reported by other studies on enhanced geothermal systems. Our results show that the greatest portion of environmental impacts originates from the construction phase (primarily due to steel for wells casing and diesel used during drilling), whilst the scenario analysis demonstrates that increasing installed capacity and cogenerating heat and power are the most effective strategies for improving the environmental performance. Our analysis also suggests that the environmental impacts may increase by ∼35% if stimulation techniques are required to increase the geothermal wells productivity. Compared to alternative energy sources, in the category climate change, UDDGP performs better than solar energy and is comparable with wind and nuclear. It is shown that the environmental benefits of geothermal energy are not straightforward and that a number of trade-offs needs to be considered when other impact categories are quantified. Image 1 • Comprehensive LCA on the first deep geothermal power plant in the UK. • Steel and diesel consumption are the greatest source of environmental impacts. • Stimulation techniques can increase the environmental impacts by as much as 35%. • Cogeneration and higher installed capacity improve the environmental performance. • Deep geothermal energy in the UK has better performance than solar. [ABSTRACT FROM AUTHOR]

The deep geothermal anomalies of the Upper Rhine Graben have long been identified (Haas and Hoffmann, 1929). They are typically attached to oil exploitation (Pechelbronn, Landau) or deep geothermal energy (Cloetingh et al.,2010; Vidal and Genter, 2018). We focus here on the area surrounding of the city of Landau (Germany) where both energies are exploited, on one hand, on the north of the city for the oil field and on the other hand, on the south of the city for the geothermal energy. In 2012, geodetic monitoring in Northern Alsace, France has begun (Heimlich, 2016). SAR acquisitions of TerraSAR-X satellite have been scheduled for a Franco-German border area west of the Rhine including the region of Landau. Direct evidence of significant surface deformation was observed in early 2014 south of the city of Landau, where unexplained cracks appeared on the geothermal power plant area during the production phase.The present work focuses on the results of the PS-InSAR analysis using StaMPS that cover the main period of displacement (2013-2014). The geodetic observations are completed by levelling measurements. These in situ measurements solve phase jump problems due to the high rate of displacement. The results show the time and space evolution of the surface displacements. It evidences also the active geological structures of the area. We developed a hydro-mechanical modelling of the deformation which gives insights into the main origin of displacement at depth related to the deep wells of the geothermal site but also questions the impact of the oil exploitation. [ABSTRACT FROM AUTHOR]

Geothermal energy development has increasingly been studied in recently decades because of its renewable and sustainable features. It can be divided into two categories: traditional geothermal (hydrothermal) systems and enhanced geothermal systems (EGS) based on the type of exploitation. The hot dry rock (HDR) in the EGS incorporates about 80% of all thermal energy, and its value is about 100–1000 times that of fossil energy. It is pivotal for geothermal wells to improve the flow conductivity of the HDR mass, enhance the communication area of natural fractures, and constitute the fracture network between injection and production wells by hydraulic treatments. While the wellbore temperature significantly decreases because of fracturing, fluid injection will induce additional thermal stresses in the cement sheath, which will aggravate its failure. Considering the radial nonuniform temperature change, this paper proposes a new thermal stress model for a casing-cement sheath-formation combined system for geothermal wells during fracturing based on elastic mechanics and thermodynamics theory. This model is solved by the Gaussian main elimination method. Based on the analytical model, the thermal stresses of cement sheath have been analyzed. The effects of the main influencing parameters on thermal stresses have also been investigated. Results show that the radial and axial tensile thermal stresses are both obviously larger than tangential tensile thermal stress. The maximum radial and axial thermal stresses always occur at the casing interface while the location of the maximum tangential thermal stress varies. Generally, thermal stresses are more likely to induce radial and axial micro cracks in the cement sheath, and the cement sheath will fail more easily at the casing interface in fracturing geothermal wells. For integrity protection of the cement sheath, a proper decrease of casing wall thickness, casing linear thermal expansion coefficient, cement sheath elasticity modulus, and an increase of the fracturing fluid temperature has been suggested. [ABSTRACT FROM AUTHOR]