Numerical Studies of Fluid-rock Interactions in EnhancedGeothermal Systems (EGS) with CO2 as Working Fluid PDF Download
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Languages : en
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There is growing interest in the novel concept of operating Enhanced Geothermal Systems (EGS) with CO2 instead of water as heat transmission fluid. Initial studies have suggested that CO2 will achieve larger rates of heat extraction, and can offer geologic storage of carbon as an ancillary benefit. Fluid-rock interactions in EGS operated with CO2 are expected to be vastly different in zones with an aqueous phase present, as compared to the central reservoir zone with anhydrous supercritical CO2. Our numerical simulations of chemically reactive transport show a combination of mineral dissolution and precipitation effects in the peripheral zone of the systems. These could impact reservoir growth and longevity, with important ramifications for sustaining energy recovery, for estimating CO2 loss rates, and for figuring tradeoffs between power generation and geologic storage of CO2.
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Languages : en
Pages :
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Book Description
There is growing interest in the novel concept of operating Enhanced Geothermal Systems (EGS) with CO2 instead of water as heat transmission fluid. Initial studies have suggested that CO2 will achieve larger rates of heat extraction, and can offer geologic storage of carbon as an ancillary benefit. Fluid-rock interactions in EGS operated with CO2 are expected to be vastly different in zones with an aqueous phase present, as compared to the central reservoir zone with anhydrous supercritical CO2. Our numerical simulations of chemically reactive transport show a combination of mineral dissolution and precipitation effects in the peripheral zone of the systems. These could impact reservoir growth and longevity, with important ramifications for sustaining energy recovery, for estimating CO2 loss rates, and for figuring tradeoffs between power generation and geologic storage of CO2.
Author: Association of Scientists, Developers and Faculties
Publisher: Association of Scientists, Developers and Faculties
ISBN: 8192974235
Category : Computers
Languages : en
Pages : 183
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Proceedings of the combined volumes of International Congress (IntCongress 2014) held at Holiday Inn Silom, Bangkok, Kingdom of Thailand between 19th November, 2014 and 21st November, 2014.
Author: Peter Birkle
Publisher: CRC Press
ISBN: 1439862990
Category : Science
Languages : en
Pages : 1004
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Book Description
In the late 18th century, Neptunists and Plutonists had controversial opinions about the formation of the Earth and its lithological units. The former believed that rocks formed from the crystallization of minerals in the early Earth's oceans, the latter believed that rocks were formed in fire. Both theories ignored the importance of continuous wat
Author: Andri Stefánsson
Publisher: Walter de Gruyter GmbH & Co KG
ISBN: 1501508296
Category : Science
Languages : en
Pages : 360
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Book Description
Volume 76 of Reviews in Mineralogy and Geochemistry presents an extended review of the topics conveyed in a short course on Geothermal Fluid Thermodynamics held prior to the 23rd Annual V.M. Goldschmidt Conference in Florence, Italy (August 24-25, 2013). It covers Thermodynamics of Geothermal Fluids, The Molecular-Scale Fundament of Geothermal Fluid Thermodynamics, Thermodynamics of Aqueous Species at High Temperatures and Pressures: Equations of State and Transport Theory, Mineral Solubility and Aqueous Speciation Under Hydrothermal Conditions to 300 °C – The Carbonate System as an Example, Thermodynamic Modeling of Fluid-Rock Interaction at Mid-Crustal to Upper-Mantle Conditions, Speciation and Transport of Metals and Metalloids in Geological Vapors, Solution Calorimetry Under Hydrothermal Conditions, Structure and Thermodynamics of Subduction Zone Fluids from Spectroscopic Studies and Thermodynamics of Organic Transformations in Hydrothermal Fluids.
Author: Hejuan Liu
Publisher: Cuvillier Verlag
ISBN: 3736948425
Category : Science
Languages : en
Pages : 285
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Book Description
In this dissertation, three simulators (i.e. TOUGH2MP, TOUGHREACT and FLAC3D) were used to simulate the complex physical and chemical interactions induced by CO2 sequestration. The simulations were done instages, ranging from the two phase (water and CO2) fluid flow (H2), through coupled hydro-mechanical effects (H2M) and geochemical responses (i.e. CO2-water-rock interactions (H2C)), to the extension of CCS to CCUS by the application of combined geothermal production and CO2 sequestration technologies. The findings of this study are essential for a thorough understanding of the complex interactions in the multiphase, multicomponent porous media controlled by different physical and chemical mechanisms. Furthermore, the simulation results will provide an invaluable reference for field operations in CCS projects, especially for the full-integration pilot scale CCS project launched in the Ordos Basin. Subsequently, a preliminary site selection scheme for the combined geothermal production and CO2 sequestration was set up, which considered various factorsinvolved in site selection, ranging from safety, economical, environmental and technical issues. This work provides an important framework for the combined geothermal production and CO2 sequestration project. However, further numerical and field studies are still needed to improve on a series of criteria and related parameters necessary for a better understanding of the technology.
Author: Esuru Rita Okoroafor
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Enhanced Geothermal Systems (EGS) offer the opportunity of exploiting the vast energy resources contained in hot impermeable rocks. In such rocks, the natural flow capacity of the system may not be sufficient to support adequate geothermal applications until it is enhanced by opening up existing fractures and propagating new fractures. Cold fluid is injected into the reservoir to exploit the energy resource, whose permeability has been enhanced. The increased permeability allows the fluid to circulate through the opened fractures to production or extraction well(s), thereby capturing and transporting the heat contained in the hot impermeable rock for power generation. Accurate prediction of the thermal performance of EGS depends on an understanding of how the heat transport is affected by the presence of the fracture(s) -- the primary flow conduit of EGS. These fractures may have aperture variability that could create channels and alter flow paths, affecting the availability of surface area for heat transfer. The overall goal of this study was to understand the fracture topology, investigate how it can impact flow and heat transport, and demonstrate ways Enhanced Geothermal Systems can be harnessed to optimize thermal performance. To achieve the goal of this study, a systematic fracture characterization approach was used, and numerical simulation models were used to study the physical processes that govern the interaction between the fluid and the rock during heat extraction from Enhanced Geothermal Systems. Using variogram modeling and Sequential Gaussian Simulation method, fracture apertures representing actual fractures were generated for lab-scale and field-scale investigations. Fracture characterization metrics such as the Joint Roughness Coefficient (JRC) and Hurst exponent were used in analyzing the data. Geometric anisotropy was a vital character of the generated fracture aperture distributions, which was seen to originate from the process of shearing or slip. Flow and heat transport relative to the direction of fracture shear was studied, with the perpendicular flow configuration being perpendicular to the direction of fracture shear. In contrast, the parallel flow configuration had flow in the same direction as the fracture shear direction. It was demonstrated in this study that the flow wetted surface area had a direct and significant contribution to the amount of heat extracted. For the lab-scale fractures, the JRC confirmed geometric anisotropy of the fracture aperture and was seen to have a direct correlation with the flow contact area. The lower the difference in JRC values between the perpendicular and parallel flow configurations, the more flow contact area expected in the perpendicular flow direction, which will lead to more heat extracted from the rock. From the variogram model parameters, it was deduced that high geometric anisotropy results in high differences in thermal drawdown and consequently a high difference in energy extracted. The thermal performance appeared to be better in the perpendicular flow configuration with a ratio of 70:30 for the lab-scale fractures. For the field-scale fractures, it was seen that most of the fracture aperture distributions with a geometric anisotropy ratio of 2 had Hurst exponents of fracture surface aperture variability found in nature. For all the fracture aperture distributions analyzed for the field scale, the perpendicular flow configuration resulted in better thermal performance than the parallel flow configuration with a ratio of 58:42. Furthermore, for the geometric anisotropy ratio of 2, the ratio was 70:30. The perpendicular flow configuration had the injected fluid move through tortuous flow paths. These tortuous flow paths contributed to more fracture surface area being contacted by the flowing fluid, leading to an improved thermal performance in that flow configuration. Throughout this study, temperature-dependent viscosity was used. However, a section of this study investigated the impact of using a constant viscosity in the thermohydraulic model. It was seen that for fractures with smooth, uniform apertures, for all temperature ranges and at the operating conditions being modeled, there was no significant difference between using a constant viscosity or a temperature-dependent viscosity in modeling an Enhanced Geothermal System. However, for fractures with spatial variations, it was determined that modeling with a temperature-dependent viscosity was necessary, especially for systems with high differences in reservoir and injection temperatures, and for fractures with high correlation lengths. The impact of thermal stresses on heat extraction was also investigated. An analog Enhanced Geothermal System, the Altona Field Laboratory, was also studied for thermo-mechanical influences. It was found out that the injection of hot water into the cold rock resulted in thermal stress generation and reduction in the aperture but did not cause significant changes to the temperature profile due to the small volumetric flow rate through the system. Also, anisotropic aperture distributions were studied to determine the impact of thermoelasticity on the heat extraction of Enhanced Geothermal Systems. It was shown that when thermoelasticity is taken into consideration, the thermal drawdown could either be improved or deteriorated depending on the nature of the aperture distribution. The impact of fracture aperture variability was investigated for Enhanced Geothermal Systems using supercritical CO2 as working fluids. It was established that CO2 as an EGS working fluid would result in better heat extracted from the system if the fractures are considered smooth, which agrees with related studies. However, where there is spatial variation in the fracture aperture, channeling could be detrimental to CO2, especially at high fracture correlation lengths and high mass flow rates, due to the high mobility of CO2. The following are the main contributions from this study. First, it has been demonstrated that heat transport is affected by the geometric anisotropy of fracture surfaces. It was determined that in most cases, flowing perpendicular to the direction of shear or slip results in more heat extracted due to more contact of the fluid with the rock while moving through tortuous flow paths. Secondly, the conditions under which a constant viscosity can be used in modeling EGS were determined. If the fractures are known to be smooth, have low correlation lengths, or have distributed surface areas, a constant viscosity can be used in the model, especially if the difference between the reservoir temperature and the injection water temperature is small. However, for anisotropic fracture surfaces, surfaces with high correlations lengths or high tortuosity, and when the difference between the reservoir temperature and injection water temperature is large, the use of constant viscosity could result in significant computational errors from the actual. Thirdly, it has been shown that thermal drawdown could either be improved or deteriorate when thermoelasticity is considered. This finding is different from studies previous studies that have looked into coupling thermohydromechanical processes for fractures with spatial variations and suggests that Enhanced Geothermal Systems may benefit from thermal stimulation. Finally, this work shows the first comparison between CO2 and water at a field scale considering fracture aperture variability. Recommended future work includes modeling of vertical fractures with spatial variations in fracture aperture to investigate how convection may impact the current findings; considering multiple fractures with spatial variations in the fracture aperture; considering non-Darcy flow in the simulation models; coupling geomechanics with the study of CO2 on fractures with spatial variations, and developing proxy models that are quicker to perform the thermohydraulic and thermohydromechanical simulations.
Author: Michael Z. Hou
Publisher: Springer Science & Business Media
ISBN: 3642378498
Category : Technology & Engineering
Languages : en
Pages : 487
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Book Description
Anthropogenic greenhouse gas emissions, energy security and sustainability are three of the greatest contemporary global challenges today. This year the Sino-German Cooperation Group “Underground Storage of CO2 and Energy”, is meeting on the 21-23 May 2013 for the second time in Goslar, Germany, to convene its 3rd Sino-German conference on the theme “Clean Energy Systems in the Subsurface: Production, Storage and Conversion”. This volume is a collection of diverse quality scientific works from different perspectives elucidating on the current developments in CO2 geologic sequestration research to reduce greenhouse emissions including measures to monitor surface leakage, groundwater quality and the integrity of caprock, while ensuring a sufficient supply of clean energy. The contributions herein have been structured into 6 major thematic research themes: Integrated Energy and Environmental Utilization of Geo-reservoirs: Law, Risk Management & Monitoring CO2 for Enhanced Gas and Oil Recovery, Coal Bedded Methane and Geothermal Systems Trapping Mechanisms and Multi-Barrier Sealing Systems for Long-Term CO2 Storage Coupled THMC-Processes and Numerical Modelling Rock Mechanical Behaviour Considering Cyclic Loading, Dilatancy, Damage, Self-sealing and Healing Underground Storage and Supply of Energy “Clean energy systems in the subsurface” will be invaluable to researchers, scientists and experts in both academia and industry trying to find a long lasting solution to the problems of global climate change, energy security and sustainability.
Author: Karsten Pruess
Publisher:
ISBN:
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Languages : en
Pages :
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The modeling of coupled thermal, hydrological, and chemical (THC) processes in geothermal systems is complicated by reservoir conditions such as high temperatures, elevated pressures and sometimes the high salinity of the formation fluid. Coupled THC models have been developed and applied to the study of enhanced geothermal systems (EGS) to forecast the long-term evolution of reservoir properties and to determine how fluid circulation within a fractured reservoir can modify its rock properties. In this study, two simulators, FRACHEM and TOUGHREACT, specifically developed to investigate EGS, were applied to model the same geothermal reservoir and to forecast reservoir evolution using their respective thermodynamic and kinetic input data. First, we report the specifics of each of these two codes regarding the calculation of activity coefficients, equilibrium constants and mineral reaction rates. Comparisons of simulation results are then made for a Soultz-type geothermal fluid (ionic strength {approx}1.8 molal), with a recent (unreleased) version of TOUGHREACT using either an extended Debye-Hueckel or Pitzer model for calculating activity coefficients, and FRACHEM using the Pitzer model as well. Despite somewhat different calculation approaches and methodologies, we observe a reasonably good agreement for most of the investigated factors. Differences in the calculation schemes typically produce less difference in model outputs than differences in input thermodynamic and kinetic data, with model results being particularly sensitive to differences in ion-interaction parameters for activity coefficient models. Differences in input thermodynamic equilibrium constants, activity coefficients, and kinetics data yield differences in calculated pH and in predicted mineral precipitation behavior and reservoir-porosity evolution. When numerically cooling a Soultz-type geothermal fluid from 200 C (initially equilibrated with calcite at pH 4.9) to 20 C and suppressing mineral precipitation, pH values calculated with FRACHEM and TOUGHREACT/Debye-Hueckel decrease by up to half a pH unit, whereas pH values calculated with TOUGHREACT/Pitzer increase by a similar amount. As a result of these differences, calcite solubilities computed using the Pitzer formalism (the more accurate approach) are up to about 1.5 orders of magnitude lower. Because of differences in Pitzer ion-interaction parameters, the calcite solubility computed with TOUGHREACT/Pitzer is also typically about 0.5 orders of magnitude lower than that computed with FRACHEM, with the latter expected to be most accurate. In a second part of this investigation, both models were applied to model the evolution of a Soultz-type geothermal reservoir under high pressure and temperature conditions. By specifying initial conditions reflecting a reservoir fluid saturated with respect to calcite (a reasonable assumption based on field data), we found that THC reservoir simulations with the three models yield similar results, including similar trends and amounts of reservoir porosity decrease over time, thus pointing to the importance of model conceptualization. This study also highlights the critical effect of input thermodynamic data on the results of reactive transport simulations, most particularly for systems involving brines.
Author:
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Category :
Languages : en
Pages :
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Numerical simulation is used to evaluate mass flow and heatextraction rates from enhanced geothermal injection-production systemsthat are operated using either CO2 or water as heat transmission fluid. For a model system patterned after the European hot dry rock experimentat Soultz, we find significantly greater heat extraction rates for CO2 ascompared to water. The strong dependence of CO2 mobility (=density/viscosity) upon temperature and pressure may lead to unusualproduction behavior, where heat extraction rates can actually increasefor a time, even as the reservoir is subject to thermaldepletion.
Author: Krishna Kumar Kamichetty
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 200
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Book Description
Permeability enhancement during stimulation in a geothermal reservoir is mainly due to the development and extension of pre-existing fractures and joints in the rockmass. The success of this technique is primarily associated with a complex interaction between thermal, hydraulic, mechanical and chemical processes within the rockmass. Various solutions have been developed with the intention of modeling each single process and eventually couple them together in order to predict the resulting permeability and size of the man-created fracture network for given injection rates and rockmass properties. Different combinations of T-H-M-C processes have been studied and are largely based on theoretical frameworks [Taron, et al, 2009]. Most of the T-H-M-C applications occur in the fields of nuclear waste disposal, gas and oil recovery, and Hot Dry Rock Geothermal Systems. In Enhanced Geothermal Systems (EGS), fluid circulation in the fractured rocks is influenced in both the short term and long term by Thermal-Hydro-Mechanical deformation [Elsworth, et al, 2009]. There are many considerations in the design of EGS and most relate to the behavior of fractures. In this work, the Thermal-Hydraulic-Mechanical behavior of the fracture aperture in a Hot Dry Rock Enhanced Geothermal System is studied through numerical simulations of the Fenton Hill model site [Cramer et al, 1979] using a three dimensional distinct element code, 3DEC. A full study of the physical processes involved and their relation with the in-situ geological, structural, mechanical and hydrogeological conditions is a constant and essential component of the work. Different values of input parameters such as Young's modulus, Poisson's ratio, mechanical stresses, thermal load and fluid flow are applied to a planar fracture, and the resultant deformation of the fracture is obtained in the form of displacements. Coupled processes such as coupled T-M and H-M methods are employed and solved for the fracture aperture changes. From the study, it is found which of these individual parameters or coupled processes have significant effect on the fracture aperture change which in turn changes the modeling methods of an Enhanced Geothermal Reservoir. As a result the study offers a reference catalog of guidelines, directions and solutions for future considerations of EGS candidates and demonstrates the capability of the model as an assessment tool for the creation of fractures for an EGS energy recovery project.
