Geothermal systems making use of advanced drilling and well stimulation techniques have the potential to provide tens to hundreds of gigawatts of clean electricity generation in the United States by ...2050. With near-zero variable costs, geothermal plants have traditionally been envisioned as providing “baseload” power, generating at their maximum rated output at all times. However, as variable renewable energy sources (VREs) see greater deployment in energy markets, baseload power is becoming increasingly less competitive relative to flexible, dispatchable generation and energy storage. Herein we conduct an analysis of the potential for future geothermal plants to provide both of these services, taking advantage of the natural properties of confined, engineered geothermal reservoirs to store energy in the form of accumulated, pressurized geofluid and provide flexible load-following generation. We develop a linear optimization model based on multi-physics reservoir simulations that captures the transient pressure and flow behaviors within a confined, engineered geothermal reservoir. We then optimize the investment decisions and hourly operations of a power plant exploiting such a reservoir against a set of historical and modeled future electricity price series. We find that operational flexibility and in-reservoir energy storage can significantly enhance the value of geothermal plants in markets with high VRE penetration, with energy value improvements of up to 60% relative to conventional baseload plants operating under identical conditions. Across a range of realistic subsurface and operational conditions, our modeling demonstrates that confined, engineered geothermal reservoirs can provide large and effectively free energy storage capacity, with round-trip storage efficiencies comparable to those of leading grid-scale energy storage technologies. Optimized operational strategies indicate that flexible geothermal plants can provide both short- and long-duration energy storage, prioritizing output during periods of high electricity prices. Sensitivity analysis assesses the variation in outcomes across a range of subsurface conditions and cost scenarios.
•Enhanced geothermal power plants are capable of time-shifting generation via modulation of injection and production rates.•Hydraulically confined reservoirs enable accumulation and discharge of pressurized geofluid.•In-reservoir energy storage can achieve durations ¿100 hours.•Energy storage is more valuable in systems with high wind and solar penetration.•Flexible operations improve the economic viability of enhanced geothermal systems.
Geothermal energy is a renewable energy source that can be found in abundance on our planet. Only a small fraction of it is currently converted to electrical power, though in recent years installed ...geothermal capacity has increased considerably all over the world. This review focuses on Enhanced Geothermal Systems (EGS), which represent a path for turning the enormous resources provided by geothermal energy into electricity for human consumption efficiently and on a large scale. The paper presents a general overview of this ever-expanding technology from its origins to the current state of the art. The Geodynamics plant in Habanero (Australia), which started up on 2 May 2013, is the first privately-run commercial EGS plant to produce electricity on a large scale. Thanks to the technological development of EGS in recent years, the future looks bright for such plants in the decades to come.
With the uncertain fractures involved in the water-rock interaction in the enhanced geothermal system (EGS) taken into account, numerical simulation of heat extraction is challenging to implement, ...especially in the situation where the EGS is conducted in a complex fracture network. In this study, a discrete fracture network (DFN) modeling procedure based on finite element method (FEM) is proposed to simulate the uncertainty of heat extraction performance in the fractured hot dry rock (HDR), in which the rock matrix and fractures are discretized into triangular elements and zero-thickness elements, respectively. To verify the effectiveness of the established numerical model, the simulation results are compared with the analytical solution and a good agreement is reached. Further, Monte Carlo simulation (MCS) method is adopted to probabilistically study the production performance of EGS considering the randomness of the fracture network. According to the MCS results, heat production performance, i.e., outlet average temperature, EGS lifetime, output thermal power, heat extraction ratio, and levelized cost of energy (LCOE), are statistically analyzed. The study results indicate that the heat extraction performance can be more effectively assessed by the probabilistic analysis, and the uncertainties involved in the heat extraction process cannot be ignored.
•Fracture uncertainty should be taken into account in water-rock interaction in EGS.•Single deterministic simulation might be insufficiently accurate.•MCS method is adopted to probabilistic study the production performance.•Probabilistic analysis provides guidance for geothermal exploitation in EGS.•Performance assessment parameters data have statistical distribution feature.
Obesity has long been considered a risk factor for postoperative adverse events in surgery. We sought to study the impact of body mass index (BMI) on the clinical outcomes of the high-risk emergency ...general surgery (EGS) elderly patients.
All EGS ≥65 years old patients in the 2007-2016 ACS-NSQIP database, identified using the variables ‘emergency’ and ‘surgspec,’ were included. Patients were classified into five groups: normal weight: BMI <25 kg/m2, overweight: BMI ≥25 kg/m2 and <30 kg/m2, Class I: BMI ≥30 kg/m2 and <35 kg/m2, Class II: BMI ≥35 kg/m2 and <40 kg/m2, and Class III: BMI ≥40 kg/m2. Patients with BMI<18.5 kg/m2 were excluded. Multivariable logistic regression models were built to assess the relationship between obesity and 30-day postoperative mortality, overall morbidity, and individual postoperative complications after adjusting for demographics (e.g., age, gender), comorbidities (e.g., diabetes mellitus, heart failure), laboratory tests (e.g., white blood cell count, albumin), and operative complexity (e.g., ASA classification).
A total of 78,704 patients were included, of which 26,011 were overweight (33.1%), 13,897 (17.6%) had Class I obesity, 5904 (7.5%) had Class II obesity, and 4490 (5.7%) had Class III obesity. On multivariable analyses, compared to the nonobese, patients who are overweight or with Class I-III obesity paradoxically had a lower risk of mortality, bleeding requiring transfusion, pneumonia, stroke and myocardial infarction (MI). Additionally, the incidence of MI and stroke decreased in a stepwise fashion as BMI progressed from overweight to severely obese (MI: OR: 0.84 0.73-0.95, OR: 0.73 0.62-0.86, OR: 0.66 0.52-0.83, OR: 0.51 0.38-0.68; stroke: OR: 0.80 0.65-0.99, OR: 0.79 0.62-1.02, OR: 0.71 0.50-1.00, OR: 0.43 0.28-0.68).
In our study of elderly EGS patients, overweight and obese patients had a lower risk of mortality, bleeding requiring transfusion, pneumonia, reintubation, stroke, and MI. Further studies are needed to confirm and investigate the obesity paradox in this patient population.
Hydroshearing has been proposed as an effective technique for enhancing the permeability of fractured geothermal reservoirs. This approach involves complicated thermo-hydro-mechanical (THM) coupling, ...but the shear behaviour and its effect on flow and heat transfer are often simplified. In this study, Barton–Bandis (BB) joint behaviour is extended to include nonlinear rock joint deformation, shear dilation and post peak softening and healing behaviours. Two models of field-scale fractured geothermal reservoirs are considered. In addition, the widely used Mohr-Coulomb (MC) model is also incorporated into the THM coupled model for comparison. The results show that cold water injection-induced high-temperature rock contraction and fluid pressure increase, reducing the effective stress and promoting fracture shear deformation and irreversible slip. Moreover, shear dilation, shear softening, and nonlinear fracture opening notably alter reservoir permeability. The two models exhibit entirely different behaviours due to different pathway evolutions and consequent pressure build-up. The BB model displays a larger shear disturbance zone than the MC model, significantly enhancing the permeability and heat extraction within the fractured reservoirs. Accurate descriptions of the mechanical behaviour of rock fractures in hydroshearing models are crucial, suggesting the potential of these models to enhance fractured reservoirs and regulate fracturing for improved geothermal heat extraction.
•Heat extraction from EGSs with heterogeneous reservoirs is modeled.•A large number of cases with various heterogeneous reservoirs are simulated.•Effects of reservoir heterogeneity on EGS heat ...extraction are analyzed.•A method is proposed to properly quantify reservoir heterogeneity.•An equation relating EGS heat extraction to reservoir heterogeneity is established.
Strong heterogeneity does exist in engineered heat reservoirs of enhanced geothermal systems (EGSs) due to different rock formation, pre-existence of natural fractures and uncertainties associated with the stimulation processes. Exploring the influence of reservoir heterogeneity on EGS heat extraction is of considerable importance to predict and fully evaluate the performance of EGSs. In this work, we take the reservoir as equivalent to a porous medium and employ a previously self-developed numerical model to conduct a series of simulations of the long-term heat extraction process of EGSs with different reservoir porosity distributions. Based on a detailed analysis to the effects of fluid seepage flow field on the heat extraction performance, we establish a method to quantify the heat extraction performance of EGSs with heterogeneous reservoirs using the seepage distribution data. We numerically test this method by taking a wide variety of heterogeneous reservoirs for EGSs. The method proves to have the capability of predicting the heat extraction performance of EGSs with miscellaneous heterogeneous reservoirs.
Display omitted
•We developed a 3D thermo-hydro model for discrete fracture networks (DFNs).•The strongly-coupled model is applicable for large-scale physical DFNs.•The industrial-scale Habanero ...geothermal reservoir validated the model.
Three-dimensional (3D) fluid flow and thermal transport modeling in discrete fracture networks (DFNs) is critical for geothermal energy recovery from enhanced geothermal systems (EGSs). Considering nonlinear fluid flow models, a 3D coupled thermo-hydro (T-H) model based on the Galerkin finite element method was developed for DFNs. Forchheimer flow was considered in this fluid flow model, and a simplified thermal transport model was adopted based on the local thermal non-equilibrium theory. Finite element spatial discretization of fluid flow and thermal transport models in DFNs was formulated. A simple upwind scheme was adopted as the numerical strategy of the thermal transport model, avoiding its solution oscillation. In addition, the proposed numerical method for the fluid flow and thermal transport was verified by comparing the model results with experimental, analytical, and numerical solutions. This approach was further applied to the modeling of heat extraction in a Habanero EGS reservoir for a period of 40 years under different injection pressures. The results demonstrated that the proposed approach was effective for simulating coupled T-H processes in 3D DFNs. With increasing the injection pressure, the power generation of reservoir increased, but its life span decreased. Injection temperature had positive effect on life span for power generation.
The objective of this paper is to introduce geothermal energy resources, utilization, development roadmap, and government support in China. Over the last 20 years, China was the first place in the ...world in direct utilization of geothermal energy with total amount reaching 17,870 MWt in 2014, and with an increasing trend annually. Compared with the rapid increase of direct utilization, the development of geothermal power generation in China is not obvious in the past 40 years, with an installed capacity of 27.78 MWe, ranking 18th in the world at present. It is reported that geothermal heating area was up to 396 million square meters with an installed capacity of 1178 MWt in 2013. Research on HDR (hot dry rock) resources is in its infancy. Considering the recoverable coefficient of 2%, energy stored in HDR at a depth of 3.0–10.0 km is 4500 times the total energy consumption in China in 2013. In order to achieve sustainable development of geothermal energy in China, attention should be paid to the following aspects in the future: technology development of EGS (enhanced geothermal system), low cost and scale-up of geothermal power generation, cascade utilization in geothermal heating, and sustainable exploitation and utilization of geothermal reservoirs.
•Geothermal resources in China are presented.•Different utilizations of geothermal energy in China are summarized.•Research on the exploitation and utilization of geothermal energy in China is reviewed.•Roadmaps of exploitation and development of geothermal energy in China are presented.•Government support for geothermal exploitation and R&D in China is overviewed.
PDF
