•The maximum magnitude of induced earthquakes does not depend on the volume of injected water, but rather on the followed injection protocol.•Seismic slip in the reactivated region of the fracture ...transitions into aseismic slip towards the end of injection and beyond shut-in.•Post-injection slip is ineffective in enhancing the maximum permeability of the reactivated region, but is crucial in stimulating regions far away from the well.•Bleeding-off at the well is a very effective strategy to arrest slip both during injection and post-injection stages, but it comes at the expense of a weaker stimulation.
To harness the immense potential of geothermal energy for non-intermittent baseload power, low-permeability crystalline hot rocks need to be hydraulically stimulated to create Enhanced Geothermal Systems (EGS) that enable economically profitable fluid flow rates. However, hydraulic stimulation is usually associated with seismic activity that has led to project cancellation in a few occasions. To improve our understanding of the coupled hydro-mechanical (HM) processes behind stimulation during both injection and post-injection stages (after shut-in), we numerically analyze three different stimulation protocols: constant-rate, step-rate, and cyclic injection with and without bleed-off after shut-in (and between cycles for the cyclic protocol). Simulation results show that the injection protocol has a higher influence on the HM response of the fracture than the total volume of injected water, which challenge scaling laws that relate the injection volume with the expected maximum magnitude of the induced earthquakes. The trade-off between maximizing permeability enhancement, while minimizing induced seismicity is not straightforward. In particular, bleeding-off the well after injection restricts induced seismicity, but at the expenses of limiting permeability enhancement. When considering stimulation of a single fault, all protocols yield comparable slip rates and, thus, magnitude of the induced earthquake, with the constant-rate injection being the fastest to induce the largest earthquake. The small differences in the HM response to hydraulic stimulation do not permit identifying a protocol that performs better than the others.
•Developed laboratory closed loop CO2 circulation apparatus to verify the thermosiphon effect.•Demonstrated the thermosiphon effect at initial injection pressures of 8.5 to 18 MPa and heater ...temperatures of 80 to 200 °C.•The apparatus showed peak heat output at injection pressures of 12–14 MPa.•Changing the medium from water to CO2 made the thermosiphon effect more feasible.
The thermosiphon effect has been shown theoretically to exist in the closed loop CO2 circulation geothermal power generation systems. We verified this effect based on previous numerical studies that determined the conditions under which the thermosiphon effect can be established and we developed laboratory experimental apparatus with conditions analogous to those in the previous studies. The results of laboratory closed loop CO2 circulation experiments using this apparatus demonstrated the thermosiphon effect at initial injection pressures from 8.5 to 18 MPa and heater temperatures from 80 to 200 °C. With this experimental apparatus, higher heater temperatures produced higher heat output at the same injection pressures, and that the peak heat output was observed at injection pressures of 12–14 MPa. Furthermore, comparing CO2 with water as the thermal transfer medium indicated that the feasibility of the thermosiphon effect was increased by changing the medium from water to CO2.
The Raft River Enhanced Geothermal System (EGS) demonstration project incorporated three hydraulic stimulations in well RRG-9 ST1 to improve geothermal production. This study investigated the ...injectivity index (injection rate divided by injection pressure) increase during long-term injection into RRG-9-ST1 after the stimulations from the perspective of thermoelasticity. We have used a one-dimensional approximate solution to estimate the injectivity/aperture change due to thermal cooling. The inferred aperture change vs. square root of time falls along a linear trend. The thermal coefficient (a combination of rock thermal properties, rock initial temperature, and injected fluid temperature) back-calculated by fitting the field injection data is in the same order of magnitude as the value directly calculated from these parameters. We have conducted fully-coupled thermal-hydro-mechanical modeling to simulate long-term circulation (cold water injection). The simulated injectivity index increased by 1.7 × 10−8 m3/(Pa·s) after 272 days of cold-water injection, similar to the field data, which increased by 2.5 × 10−8 m3/(Pa·s). Both the trend and the magnitude of the simulated injectivity change match with the field data recorded at Raft River. The injectivity index increased faster at the beginning and then the rate of increase became smaller with time. The injectivity index increase is hypothesized to be the result of fracture aperture increase due to cooling effects. The simulated fracture aperture at the injection well increased by 0.64 mm, and the simulated maximum fracture aperture increased by 1.93 mm. The trend of the simulated aperture change also matches the value interpreted from the field data using the 1D approximate solutions. The study suggests that cooling is the major reason for the injectivity increase at Raft River EGS during the long-term injection. More broadly, cold water injection could serve as a method to increase the injectivity in other settings after high-volume and high rate/pressure hydraulic stimulation
Continuous microseismic monitoring using three-component (3C) accelerometers deployed in multiple boreholes allows for tracking the detailed evaluation of mesoscale (∼10 m scale) fracture growth ...during the fracture stimulation experiments at the first Enhanced Geothermal Systems (EGS) Collab testbed. Building on a well-constrained microseismic event catalog, we invert for moment tensor of the events to better understand the fracture geometry and stress orientations. However, it is challenging because of the unknown orientation of 3C accelerometers and low signal-to-noise-ratio nature of high-frequency (several kHz) monitoring. To address these challenges, we first perform the hodogram analysis on the continuous active-source seismic monitoring (CASSM) data to determine the orientations of the 18 3C accelerometers. We then apply the principal component analysis (PCA) to the observed microseismic waveforms to improve the signal-to-noise ratios. We perform a grid search for the full moment tensor by fitting the PCA-denoised waveforms at a frequency range of 5 to 8 kHz. The moment tensor results show both the creation of hydraulic fractures and the reactivation of natural fractures during the hydraulic stimulations. Our stress inversion based on the inverted moment tensors reveals the alteration of stress regime caused by hydraulic fracture stimulations.
The purpose of this study is to examine the impact of green tax incentives such as investment tax credit and taxable income deductions related to the environmental sustainability and climate change ...which are becoming more popular in developing countries, whereas introducing green tax incentives related to the environment and climate change helps and meets the sustainability objectives of growth and development. For this purpose, we selected the top 100 listed companies on the Swedish stock market (SSM), Nasdaq Stockholm (SN), in order to better understand the real facts and figures of green tax environment. This study uses a longitudinal research design because sample observations vary across firms and over a short time and conducts probit and logistic regression to identify the beneficiaries of the tax incentives. The findings show that different firm-level characteristics significantly impact the probability of being an ITC beneficiary.
•A fully coupled THM model for simulating flow channeling in EGS heat production.•Aperture heterogeneity causes channelized flow and exacerbates flow channeling.•Longer aperture correlation length ...leads to worse and more variable performance.•Aperture standard deviation affects heat production when correlation length is long.
The evolution of flow pattern along a single fracture and its effects on heat production is a fundamental problem in the assessments of engineered geothermal systems (EGS). The channelized flow pattern associated with ubiquitous heterogeneity in fracture aperture distribution causes non-uniform temperature decrease in the rock body, which makes the flow increasingly concentrated into some preferential paths through the action of thermal stress. This mechanism may cause rapid heat production deterioration of EGS reservoirs. In this study, we investigated the effects of aperture heterogeneity on flow pattern evolution in a single fracture in a low-permeability crystalline formation. We developed a numerical model on the platform of GEOS to simulate the coupled thermo-hydro-mechanical processes in a penny-shaped fracture accessed via an injection well and a production well. We find that aperture heterogeneity generally exacerbates flow channeling and reservoir performance generally decreases with longer correlation length of aperture field. The expected production life is highly variable (5 years to beyond 30 years) when the aperture correlation length is longer than 1/5 of the well distance, whereas a heterogeneous fracture behaves similar to a homogeneous one when the correlation length is much shorter than the well distance. Besides, the mean production life decreases with greater aperture standard deviation only when the correlation length is relatively long. Although flow channeling is inevitable, initial aperture fields and well locations that enable tortuous preferential paths tend to deliver long heat production lives.
Under the significant pressure to diversify energy supply and reduce the dependence on fossil fuels, harnessing the vast geothermal resources has been made a priority in China's renewable energy ...development plans. This review provided an overview on the development of geothermal power generation and direct use in China, identified the key barriers for geothermal energy utilization, particularly in power generation, and proposed corresponding measures for boosting the growth of geothermal industry. Little progress was made in geothermal power generation over the past decades, while geothermal direct use, particularly geothermal heat pumps (GHPs) and district heating, has been growing quickly. Development of geothermal power generation was primarily limited by the lack of high temperature hydrothermal resources near the major demand centers. A series of technological challenges associated with drilling under extremely high pressure and temperature conditions, transportation of heavy equipment, long-distance electricity transmission, and hot dry rock (HDR) exploitation, also hindered large-scale development of geothermal resources for power generation and district heating. There were no social barriers for geothermal exploitation except in hot spring tourism areas, while the high cost could limit the consumer acceptance of geothermal heating/cooling solutions. Significant investment in research and development of enhanced geothermal system (EGS) technologies for exploiting HDR resources and establishment of favorable policy instruments are recommended as key technological and policy measures to accelerate the growth of geothermal energy market, while the potential social barriers for the development EGS projects in the densely populated areas should also be recognized and mitigated in the future.
•Extracting lithium from brine is a challenge because it is a potential resource.•Geothermal fluids possess a significant concentration of lithium which is a vital element in electric vehicles and ...energy storage-battery applications.•Various methods have been used to remove lithium from geothermal brine.•The removal of lithium from the geothermal fluid is considered a highly economical alternative mining method in the long term.
Energy transition elements (Li, Ni, Co, Fe, Cu) are gaining importance due to their ability to provide energy and play an important role as primary energy sources. Because of the energy density and power density, Li-ion batteries have the edge over other batteries. Li is distributed in various rock-forming minerals and brines, and geothermal waters. Though lithium-bearing minerals are spread over a broad geographic region, these minerals are confined to certain countries with substantial economic potential. Li is extensively used in batteries, and battery-driven vehicles are growing exponentially to meet the carbon reduction goal of the Paris agreement in 2015 and signed by more than 50 percent of the countries. Nearly 55 million cars supported by Li batteries are expected to roll out by 2030. While this is the demand, its occurrence and concentration/extraction processes are not keeping pace with this demand. The extraction of Li from its ore is an energy-intensive process involving many fossil fuel-based energies. To recover one ton of Li metal, nearly 5 to 6 tons of CO2 is emitted. The CO2 emissions of 28 kWh LFP, NMC, and LMO batteries vary from 5600 to 2705 kg CO2-eq. The end-of-life emissions of an internal combustion engine (ICE) vehicle are 400 kg CO2/vehicle, while Li Battery supports 500 kg/vehicle. The quantity of Li required for a 24 kWh average capacity leaf battery is about 137 g/kWh. While emissions are associated with the manufacturing of the batteries, emissions are also associated with a way that while they are recharged as the recharging source is fossil fuel-based energy. The best option to meet zero net carbon emissions by 2050, as envisaged by International Energy Agency (IEA), is to recover Li from geothermal brines and use geothermal energy for recharging. While hydrothermal energy sources are site-specific, enhanced geothermal system (EGS) based geothermal energy is not site-specific and is found wherever high radiogenic granites are available. High radiogenic granites are widely distributed, and heat recovered from EGS sources can provide clean energy and heat. Extraction of lithium from geothermal waters and using geothermal energy for recharging the batteries will drastically reduce CO2 emissions. It will drive the world towards Net Zero Emissions (NZE) scenario in the future. This is being practiced in Turkey. Future research should develop technology to recover Li from geothermal fluids with low concentration and support EGS development.
Evacuation leaders and/ or equipment provide route and exit information for people and guide them to the expected destinations, which could make crowd evacuation more efficient in case of ...emergency. The purpose of this paper is to provide an overview of recent advances in guided crowd evacuation. Different guided crowd evacuation approaches are classified according to guidance approaches and technologies. A comprehensive analysis and comparison of crowd evacuation with static signage, dynamic signage, trained leader, mobile devices, mobile robot and wireless sensor networks are presented based on a single guidance mode perspective. In addition, the different evacuation guidance systems that use technology automated methods of evacuation are reviewed from a systemʼ s perspective. Future research in the area of crowd evacuation are also discussed.
Petrothermal reservoirs contain a tremendous technical potential without major regional restrictions. The application of supercritical CO2 (sCO2) as a heat carrier might be a promising alternative to ...the commonly discussed usage of water. This study evaluates both heat carriers for a CHP application. A novel CHP plant layout for a thermosiphon with direct utilization of sCO2 for power generation and a pumped brine system with a parallel CHP plant and power generation by an Organic Rankine Cycle (ORC) are compared for a defined mass flow rate of 225 kg/s and reservoir conditions of 180 °C and 49 MPa. For the ORC with R245fa the annual amount of net electricity is 3% higher than for the ORC with R1233zd(E) and 8% higher than for the sCO2 case. The net power of the sCO2 plant displays a significantly higher sensitivity to changes of the heat demand compared to the brine-ORC system. While the average exergetic efficiency for the brine concept is 40.9% for R245fa and 40.0% for R1233zd(E), respectively, the sCO2 concept reaches an average efficiency of 72.6%. Finally, two different operation strategies for the sCO2 CHP plant are investigated against the background of potential turbine part-load models.
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•Petrothermal resources have a tremendous potential for heat and power generation.•Supercritical sCO2 and water are compared as potential heat carriers.•sCO2 displays a higher sensitivity to varying heat demand.•The selected turbine-part load model has an significant impact.
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