Understanding the cause of the November 2017 Pohang main shock is of considerable importance to the future of the geothermal industry because of its large magnitude compared to prior expectations ...based on case histories of other projects involving underground fluid injection. Of the three possibilities – induced, triggered or natural, “induced” can be ruled out based on the disproportionately large seismic moment of the main shock. Furthermore, whether natural or triggered, the source of seismic hazard at Pohang was tectonic strain accumulation, not fluid injection. Arguably, the most timely indicator of seismic hazard and risk in the environs of Pohang was the September 2016 Mw 5.4 Gyeongju earthquake, which was natural and located about 40 km south of Pohang along the same active fault system.
Assessment of operative risk in geriatric patients undergoing emergency general surgery (EGS) is challenging. Frailty is an established measure for risk assessment in surgical cases. The aim of our ...study was to validate a modified 15-variable EGS-specific frailty index (EGSFI).
We prospectively collected geriatric (age older than 65 years) EGS patients for 2 years. Postoperative complications were collected. Frailty index was calculated for 200 patients based on their preadmission condition using 50-variable modified Rockwood frailty index. Emergency general surgery-specific frailty index was developed based on the regression model for complications and the most significant factors in the frailty index. Receiver operating characteristic curve analysis was performed to determine cutoff for frail status. We validated our results using 60 patients for predicting complications.
A total of 260 patients (developing, 200; validation, 60) were enrolled in this study. Mean age was 71 ± 11 years, and 33% developed complications. Most common complications were pneumonia (12%), urinary tract infection (9%), and wound infection (7%). Univariate analysis identified 15 variables significantly associated with complications that were used to develop the EGSFI. A cutoff frailty score of 0.325 was identified using receiver operating characteristic curve analysis for frail status. Sixty patients (frail, 18; nonfrail, 42) were enrolled in the validation cohort. Frail patients were more likely to have postoperative complications (47% vs. 20%; p < 0.001) compared to nonfrail patients. Frail status based on EGSFI was a significant predictor of postoperative complications (odds ratio, 7.3; 95% confidence interval, 1.7-19.8; p = 0.006). Age was not associated with postoperative complications (odds ratio, 0.99; 95% confidence interval, 0.92-1.06; p = 0.86).
The 15-variable validated EGSFI is a simple and reliable bedside tool to determine the frailty status of patients undergoing EGS. Frail status as determined by the EGSFI is an independent predictor of postoperative complications and mortality in geriatric EGS patients.
Prognostic study, level II.
•Reservoir properties and working fluid types for EGS are summarized based on related global projects.•The dissolution or precipitation process of common minerals and its influencing factors are ...described in details.•Salt precipitation in saline aquifers and its effect on reservoir permeability are illustrated.•The impacts of working fluid-rock interactions on reservoir permeability, mechanical properties and heat extraction capacity are summarized.•The prospects of CO2-EGS and some limitations of current studies have been discussed.
Geothermal energy from Hot Dry Rock (HDR) with poor permeability is recognized as a potential future energy source, and it can be exploited by Enhanced Geothermal System (EGS) technology. In this paper, geochemical mechanisms of typical working fluids interacting with the primary rock types of EGS reservoirs, and their impacts on reservoir properties are summarized. While traditional EGS primarily utilizes granite reservoirs, the technology has been gradually extended to include sandstone and carbonate rock formations. Regarding the working fluid, water is currently the only one that has been put into practice. Mineral dissolution and precipitation and salt precipitation are the two dominant geochemical mechanisms during the heat extraction process using water or CO2. These mechanisms are influenced by fluid pH, reservoir temperature, pressure, and flow rate. The dissolution of feldspar minerals plays an important role in increasing permeability and the availability of cations for the precipitation of secondary minerals. Carbonate minerals are often the quickest to respond to changes in fluid chemistry induced by CO2 injection, and the re-precipitation of carbonates is triggered by increasing temperature and pH. It is difficult to predict variations in permeability due to the involvement of many factors, including particle sizes and salt precipitation. The mechanical properties of rocks are significantly weakened following interactions with working fluids. The weakening effect on rock mechanical properties is more pronounced when CO2 is injected into water-saturated formations. Although water-rock interactions can change the thermal conductivity of the rock, the characteristics of fracture networks appear to be of greater importance because working fluids mainly flow through fractures, and maximizing heat extraction from EGS depends strongly on effective circulation. Further economic evaluations for CO2-EGS are necessary to confirm the economic viability of using CO2 as a working fluid. Additionally, the THMCB (Thermo-Hydro-Mechanical-Chemical-Biological) coupling effects during water/CO2 interactions should be comprehensively studied based on both long-term field tests and truly integrated numerical models.
•We successfully modified the PFA methodology to identify favorable areas for superhot EGS at Newberry Volcano in 3D.•Key components of superhot EGS plays were developed, including heat source, ...thermal insulation, and producibility.•Uncertainty was also quantified in 3D for datasets which provided enough information to do so.•Two different methods were used to weight exploration datasets, and the resulting favorability models compared.
The DErisking Exploration for multiple geothermal Plays in magmatic ENvironments (DEEPEN) project aims to de-risk exploration of geothermal plays in magmatic systems, with a focus on superhot and supercritical geothermal systems. This article presents advancements in geoscientific assessment of superhot enhanced geothermal system (EGS) resources as part of the DEEPEN project, particularly in exploration and identification of these systems. While there exists a general consensus on key components of conventional hydrothermal systems, there has not been a prior consensus on such components for EGS, let alone superhot EGS. The DEEPEN project identified these key components for superhot EGS plays, and used them to modify the traditional geothermal play fairway analysis (PFA) approach to identify favorable areas in superhot EGS plays in 3D. This was done through modeling both favorability and uncertainty separately for each key component of a superhot EGS play, incorporating diverse 3D geoscientific datasets, including geologic features, models produced from direct observations, single inversions, and joint inversions. The PFA is applied to Newberry Volcano as a form of validation. The results appear to validate the methodology, aligning with expectations derived from conceptual modeling, and highlighting the area targeted for EGS stimulation well NWG 55-29 as favorable, and suggesting potential additional areas worthy of exploration at Newberry.
This paper presents a coupled Wellbore-Reservoir-Organic Rankine Cycle (ORC) power plant model for sustainable and efficient use of multiple-fractures Enhanced Geothermal System with simulations ...conducted over 40 years of operation time. A multi-objective optimization of the ORC under off-design conditions was conducted using constrained NSGA-II technique considering specific investment cost, energy and exergy efficiencies as objective functions. Twenty working fluids were considered to select the best one based on the turbine inlet superheated vapor condition, the lowest specific investment cost, the best energy and exergy efficiencies. Optimal operations conditions were determined for each working fluid considering turbine inlet temperature, turbine inlet pressure, condenser temperature, refrigerant mass flow rate, and length, tubes number, inner diameter and outer diameter of evaporator and condenser, isentropic turbine efficiency, isentropic pump efficiency as decision variables. The results show that the working fluids have a significant effect on the reinjection geofluid temperature and slight effect on the production temperature. The best performing working fluid was R1233zd(E) providing an energy efficiency of 19.2–19.32% and the exergy efficiency found is between 56.4% and 58.44% over the 40 years of production in off-design conditions and optimal operation conditions. The energy efficiency and the exergy efficiency decrease with increasing condenser temperature.
•A new wellbores-reservoir-ORC model is performed for efficient energy management.•Multi-objective optimization of geothermal ORC under off-design conditions.•Energy and exergy efficiencies and economic performance were optimized with NSGA-II.•R1233zd(E), a hydrofluoroolefin refrigerant was the best performing working fluid.•New combination of operation parameters to avoid droplets formation in the turbine.
In the present study, activated carbon (AC) was prepared from Eucalyptus globulus seed (EGS) by a simple hydrothermal method followed by chemical activation using potassium hydroxide as the ...activating agent under different carbonization temperatures. X-ray diffraction and Raman spectroscopic analysis confirmed the amorphous and turbostratic disordered nature of the carbon. FT-IR analysis of the activated carbon samples shows the presence of N and O functional groups. Brunauer-Emmett-Teller (BET) specific surface area analysis of EGS derived activated carbon at 900 °C showed the highest specific surface area of 2388.38 m2g−1 and exhibited a specific capacitance of 150 Fg−1. The appearance of small and large graphitic pores with random orientation and approximately 88.3 wt% of carbon and 11.7 wt% of oxygen were confirmed by SEM/EDX analyses. Further to understand the electrocatalytic nature of the synthesizing carbon, the material was tested as an electrode for supercapacitors. The electrochemical performance was demonstrated by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance (EIS) studies. The electrochemical properties of EGS derived activated carbon demonstrate its potential application as high-performance and low-cost supercapacitor electrode material to fabricate energy storage devices.
Display omitted
•Eucalyptus globulus seed-derived carbon exhibited a specific surface area of 2388.38 m2g−1.•Exhibited a specific capacitance of 150 F g−1 comparable with other biomass derived carbon•An economically feasible electrode material for supercapacitor application
A conceptual Enhanced Geothermal System (EGS) model, where water is circulated through a pair of parallel injection and production wells connected by a set of single large wing fractures, is ...designed, modeled, and evaluated in this work. The water circulation and heat extraction in the fractured reservoirs is modeled as a fully coupled process of fluid flow and heat transport. Using a newly developed, open-source, finite element based geothermal simulation code, FALCON, simulation results were obtained for a 30-year operation at a depth of 3 km and geothermal gradient of 65°C per km of depth. With a sensitivity study of the heat production to the design parameters, preferable fracture horizontal spacing, downward deviation angle of the parallel wells, and injection flow rate are recommended. Upscaling calculations of the developed EGS model have shown that, an industrial production-level system may be achievable if it consists of 40 equidistant fractures that connect two 1.2 km long parallel well sections with a well separation of 500 m; and if a system of these dimensions operates for 30 years at a flow rate of 0.1 m3/s, with an electric power output at least 5 MW and pumping power of less than 1 MW. In particular, the performance metrics demonstrated in this work match well with those suggested by others, thus indicating the general applicability of our conceptual models.
•A new EGS heat extraction model is designed, modeled, and evaluated.•A newly developed and validated open-source geothermal simulation code is employed.•The sensitivity of reservoir heat production to key EGS design parameters is analyzed.•Based on the new model, design parameters for industrial-level power supply are suggested.
EGS (Enhanced Geothermal System) is a potential way to utilize geothermal energy efficiently. In present work, a three-dimensional physical model, a single fracture with undulated surface morphology ...in hot dry rock is constructed. Supercritical CO2 is used as working fluid, and its convection heat transfer characteristics in fracture is numerically investigated. The influence of flow rate, inlet temperature, and reservoir pressure on convection heat transfer are probed. The results indicate that the local convection heat transfer coefficients at upper wall and lower wall of fracture show opposite variation trend at corresponding positions, and it varies with the undulation of surface morphology. In addition, the local convection heat transfer coefficients rise with the decrease of flow rate, the increase of pressure and inlet temperature. Furthermore, the correlation of normalized convection coefficient Nusselt number of supercritical CO2 in fracture is obtained.
Geothermal power is being regarded as depending on techniques derived from hydrocarbon production in worldwide current strategy. However, it has artificially been developed far less than its natural ...potentials due to technical restrictions. This paper introduces the Enhanced Geothermal System based on Excavation (EGS-E), which is an innovative scheme of geothermal energy extraction. Then, based on cohesion-weakening-friction-strengthening model (CWFS) and literature investigation of granite test at high temperature, the initiation, propagation of excavation damaged zones (EDZs) under unloading and the EDZs scale in EGS-E closed to hydrostatic pressure state is studied. Finally, we have a discussion about the further evolution of surrounding rock stress and EDZs during ventilation is studied by thermal-mechanical coupling. The results show that the influence of high temperature damage on the mechanical parameters of granite should be considered; Lateral pressure coefficient affects the fracture morphology and scale of tunnel surrounding rock, and EDZs area is larger when the lateral pressure coefficient is 1.0 or 1.2; Ventilation of high temperature and high in-situ stress tunnel have a significant effect on the EDZs scale; Additional tensile stress is generated in the shallow of tunnel surrounding rock, and the compressive stress concentration transfers to the deep. EDZs experiences three expansion stages of slow, rapid and deceleration with cooling time, and the thermal insulation layer prolongs the slow growth stage.
PDF
