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Yuan Wang - One of the best experts on this subject based on the ideXlab platform.

  • a numerical manifold method model for analyzing fully coupled hydro mechanical processes in Porous Rock masses with discrete fractures
    Advances in Water Resources, 2017
    Co-Authors: Mengsu Hu, Jonny Rutqvist, Yuan Wang
    Abstract:

    Abstract In this study, a numerical manifold method (NMM) model was developed for fully coupled analysis of hydro-mechanical (HM) processes in Porous Rock masses with discrete fractures. Using an NMM two-cover-mesh system of mathematical and physical covers, fractures are conveniently discretized by dividing the mathematical cover along fracture traces to physical cover, resulting in a discontinuous model on a non-conforming mesh. In this model, discrete fracture deformation (e.g. open and slip) and fracture fluid flow within a permeable and deformable Porous Rock matrix are rigorously considered. For Porous Rock, direct pore-volume coupling was modeled based on an energy-work scheme. For mechanical analysis of fractures, a fracture constitutive model for mechanically open states was introduced. For fluid flow in fractures, both along-fracture and normal-to-fracture fluid flow are modeled without introducing additional degrees of freedom. When the mechanical aperture of a fracture is changing, its hydraulic aperture and hydraulic conductivity is updated. At the same time, under the effect of coupled deformation and fluid flow, the contact state may dynamically change, and the corresponding contact constraint is updated each time step. Therefore, indirect coupling is realized under stringent considerations of coupled HM effects and fracture constitutive behavior transfer dynamically. To verify the new model, examples involving deformable Porous media containing a single and two sets of fractures were designed, showing good accuracy. Last, the model was applied to analyze coupled HM behavior of fractured Porous Rock domains with complex fracture networks under effects of loading and injection.

  • fully coupled hydro mechanical numerical manifold modeling of Porous Rock with dominant fractures
    Acta Geotechnica, 2017
    Co-Authors: Mengsu Hu, Yuan Wang, Jonny Rutqvist
    Abstract:

    Coupled hydro-mechanical (HM) processes are significant in geological engineering such as oil and gas extraction, geothermal energy, nuclear waste disposal and for the safety assessment of dam foundations and Rock slopes, where the geological media usually consist of fractured Rock masses. In this study, we developed a model for the analysis of coupled hydro-mechanical processes in Porous Rock containing dominant fractures, by using the numerical manifold method (NMM). In the current model, the fractures are regarded as different material domains from surrounding Rock, i.e., finite-thickness fracture zones as Porous media. Compared with the Rock matrix, these fractured Porous media are characterized with nonlinear behavior of hydraulic and mechanical properties, involving not only direct (poroelastic) coupling but also indirect (property change) coupling. By combining the potential energy associated with mechanical responses, fluid flow and solid–fluid interactions, a new formulation for direct HM coupling in Porous media is established. For indirect coupling associated with fracture opening/closure, we developed a new approach implicitly considering the nonlinear properties by directly assembling the corresponding strain energy. Compared with traditional methods with approximation of the nonlinear constitutive equations, this new formulation achieves a more accurate representation of the nonlinear behavior. We implemented the new model for coupled HM analysis in NMM, which has fixed mathematical grid and accurate integration, and developed a new computer code. We tested the code for direct coupling on two classical poroelastic problems with coarse mesh and compared the results with the analytical solutions, achieving excellent agreement, respectively. Finally, we tested for indirect coupling on models with a single dominant fracture and obtained reasonable results. The current poroelastic NNM model with a continuous finite-thickness fracture zone will be further developed considering thin fractures in a discontinuous approach for a comprehensive model for HM analysis in fractured Porous Rock masses.

Mengsu Hu - One of the best experts on this subject based on the ideXlab platform.

  • a numerical manifold method model for analyzing fully coupled hydro mechanical processes in Porous Rock masses with discrete fractures
    Advances in Water Resources, 2017
    Co-Authors: Mengsu Hu, Jonny Rutqvist, Yuan Wang
    Abstract:

    Abstract In this study, a numerical manifold method (NMM) model was developed for fully coupled analysis of hydro-mechanical (HM) processes in Porous Rock masses with discrete fractures. Using an NMM two-cover-mesh system of mathematical and physical covers, fractures are conveniently discretized by dividing the mathematical cover along fracture traces to physical cover, resulting in a discontinuous model on a non-conforming mesh. In this model, discrete fracture deformation (e.g. open and slip) and fracture fluid flow within a permeable and deformable Porous Rock matrix are rigorously considered. For Porous Rock, direct pore-volume coupling was modeled based on an energy-work scheme. For mechanical analysis of fractures, a fracture constitutive model for mechanically open states was introduced. For fluid flow in fractures, both along-fracture and normal-to-fracture fluid flow are modeled without introducing additional degrees of freedom. When the mechanical aperture of a fracture is changing, its hydraulic aperture and hydraulic conductivity is updated. At the same time, under the effect of coupled deformation and fluid flow, the contact state may dynamically change, and the corresponding contact constraint is updated each time step. Therefore, indirect coupling is realized under stringent considerations of coupled HM effects and fracture constitutive behavior transfer dynamically. To verify the new model, examples involving deformable Porous media containing a single and two sets of fractures were designed, showing good accuracy. Last, the model was applied to analyze coupled HM behavior of fractured Porous Rock domains with complex fracture networks under effects of loading and injection.

  • fully coupled hydro mechanical numerical manifold modeling of Porous Rock with dominant fractures
    Acta Geotechnica, 2017
    Co-Authors: Mengsu Hu, Yuan Wang, Jonny Rutqvist
    Abstract:

    Coupled hydro-mechanical (HM) processes are significant in geological engineering such as oil and gas extraction, geothermal energy, nuclear waste disposal and for the safety assessment of dam foundations and Rock slopes, where the geological media usually consist of fractured Rock masses. In this study, we developed a model for the analysis of coupled hydro-mechanical processes in Porous Rock containing dominant fractures, by using the numerical manifold method (NMM). In the current model, the fractures are regarded as different material domains from surrounding Rock, i.e., finite-thickness fracture zones as Porous media. Compared with the Rock matrix, these fractured Porous media are characterized with nonlinear behavior of hydraulic and mechanical properties, involving not only direct (poroelastic) coupling but also indirect (property change) coupling. By combining the potential energy associated with mechanical responses, fluid flow and solid–fluid interactions, a new formulation for direct HM coupling in Porous media is established. For indirect coupling associated with fracture opening/closure, we developed a new approach implicitly considering the nonlinear properties by directly assembling the corresponding strain energy. Compared with traditional methods with approximation of the nonlinear constitutive equations, this new formulation achieves a more accurate representation of the nonlinear behavior. We implemented the new model for coupled HM analysis in NMM, which has fixed mathematical grid and accurate integration, and developed a new computer code. We tested the code for direct coupling on two classical poroelastic problems with coarse mesh and compared the results with the analytical solutions, achieving excellent agreement, respectively. Finally, we tested for indirect coupling on models with a single dominant fracture and obtained reasonable results. The current poroelastic NNM model with a continuous finite-thickness fracture zone will be further developed considering thin fractures in a discontinuous approach for a comprehensive model for HM analysis in fractured Porous Rock masses.

Yu Zhao - One of the best experts on this subject based on the ideXlab platform.

  • an elastic stress strain relationship for Porous Rock under anisotropic stress conditions
    Rock Mechanics and Rock Engineering, 2012
    Co-Authors: Yu Zhao
    Abstract:

    A stress–strain relationship within Porous Rock under anisotropic stress conditions is required for modeling coupled hydromechanical processes associated with a number of practical applications. In this study, a three-dimensional stress–strain relationship is proposed for Porous Rock under elastic and anisotropic stress conditions. This relationship is a macroscopic-scale approximation that uses a natural-strain-based Hooke’s law to describe deformation within a fraction of pores and an engineering-strain-based Hooke’s law to describe deformation within the other part. This new relationship is evaluated using data from a number of uniaxial and triaxial tests published in the literature. Based on this new stress–strain relationship, we also develop constitutive relationships among stress, strain, and related stress-dependent hydraulic/mechanical properties (such as compressibility, shear modulus, and porosity). These relationships are demonstrated to be consistent with experimental observations.

  • An Elastic Stress–Strain Relationship for Porous Rock Under Anisotropic Stress Conditions
    Rock Mechanics and Rock Engineering, 2011
    Co-Authors: Yu Zhao
    Abstract:

    A stress–strain relationship within Porous Rock under anisotropic stress conditions is required for modeling coupled hydromechanical processes associated with a number of practical applications. In this study, a three-dimensional stress–strain relationship is proposed for Porous Rock under elastic and anisotropic stress conditions. This relationship is a macroscopic-scale approximation that uses a natural-strain-based Hooke’s law to describe deformation within a fraction of pores and an engineering-strain-based Hooke’s law to describe deformation within the other part. This new relationship is evaluated using data from a number of uniaxial and triaxial tests published in the literature. Based on this new stress–strain relationship, we also develop constitutive relationships among stress, strain, and related stress-dependent hydraulic/mechanical properties (such as compressibility, shear modulus, and porosity). These relationships are demonstrated to be consistent with experimental observations.

Jonny Rutqvist - One of the best experts on this subject based on the ideXlab platform.

  • a numerical manifold method model for analyzing fully coupled hydro mechanical processes in Porous Rock masses with discrete fractures
    Advances in Water Resources, 2017
    Co-Authors: Mengsu Hu, Jonny Rutqvist, Yuan Wang
    Abstract:

    Abstract In this study, a numerical manifold method (NMM) model was developed for fully coupled analysis of hydro-mechanical (HM) processes in Porous Rock masses with discrete fractures. Using an NMM two-cover-mesh system of mathematical and physical covers, fractures are conveniently discretized by dividing the mathematical cover along fracture traces to physical cover, resulting in a discontinuous model on a non-conforming mesh. In this model, discrete fracture deformation (e.g. open and slip) and fracture fluid flow within a permeable and deformable Porous Rock matrix are rigorously considered. For Porous Rock, direct pore-volume coupling was modeled based on an energy-work scheme. For mechanical analysis of fractures, a fracture constitutive model for mechanically open states was introduced. For fluid flow in fractures, both along-fracture and normal-to-fracture fluid flow are modeled without introducing additional degrees of freedom. When the mechanical aperture of a fracture is changing, its hydraulic aperture and hydraulic conductivity is updated. At the same time, under the effect of coupled deformation and fluid flow, the contact state may dynamically change, and the corresponding contact constraint is updated each time step. Therefore, indirect coupling is realized under stringent considerations of coupled HM effects and fracture constitutive behavior transfer dynamically. To verify the new model, examples involving deformable Porous media containing a single and two sets of fractures were designed, showing good accuracy. Last, the model was applied to analyze coupled HM behavior of fractured Porous Rock domains with complex fracture networks under effects of loading and injection.

  • fully coupled hydro mechanical numerical manifold modeling of Porous Rock with dominant fractures
    Acta Geotechnica, 2017
    Co-Authors: Mengsu Hu, Yuan Wang, Jonny Rutqvist
    Abstract:

    Coupled hydro-mechanical (HM) processes are significant in geological engineering such as oil and gas extraction, geothermal energy, nuclear waste disposal and for the safety assessment of dam foundations and Rock slopes, where the geological media usually consist of fractured Rock masses. In this study, we developed a model for the analysis of coupled hydro-mechanical processes in Porous Rock containing dominant fractures, by using the numerical manifold method (NMM). In the current model, the fractures are regarded as different material domains from surrounding Rock, i.e., finite-thickness fracture zones as Porous media. Compared with the Rock matrix, these fractured Porous media are characterized with nonlinear behavior of hydraulic and mechanical properties, involving not only direct (poroelastic) coupling but also indirect (property change) coupling. By combining the potential energy associated with mechanical responses, fluid flow and solid–fluid interactions, a new formulation for direct HM coupling in Porous media is established. For indirect coupling associated with fracture opening/closure, we developed a new approach implicitly considering the nonlinear properties by directly assembling the corresponding strain energy. Compared with traditional methods with approximation of the nonlinear constitutive equations, this new formulation achieves a more accurate representation of the nonlinear behavior. We implemented the new model for coupled HM analysis in NMM, which has fixed mathematical grid and accurate integration, and developed a new computer code. We tested the code for direct coupling on two classical poroelastic problems with coarse mesh and compared the results with the analytical solutions, achieving excellent agreement, respectively. Finally, we tested for indirect coupling on models with a single dominant fracture and obtained reasonable results. The current poroelastic NNM model with a continuous finite-thickness fracture zone will be further developed considering thin fractures in a discontinuous approach for a comprehensive model for HM analysis in fractured Porous Rock masses.

  • a modeling approach for analysis of coupled multiphase fluid flow heat transfer and deformation in fractured Porous Rock
    International Journal of Rock Mechanics and Mining Sciences, 2002
    Co-Authors: Jonny Rutqvist, Yushu Wu, Chinfu Tsang, G S Bodvarsson
    Abstract:

    Abstract This paper presents the methodology in which two computer codes—TOUGH2 and FLAC3D—are linked and jointly executed for coupled thermal–hydrologic–mechanical (THM) analysis of multiphase fluid flow, heat transfer, and deformation in fractured and Porous Rock. TOUGH2 is a well-established code for geohydrological analysis with multiphase, multicomponent fluid flow and heat transport, while FLAC3D is a widely used commercial code that is designed for Rock and soil mechanics with thermomechanical and hydromechanical interactions. In this study, the codes are sequentially executed and linked through external coupling modules: one that dictates changes in effective stress as a function of multi-phase pore pressure and thermal expansion, and one that corrects porosity, permeability, and capillary pressure for changes in stress. The capability of a linked TOUGH-FLAC simulator is demonstrated on two complex coupled problems related to injection and storage of carbon dioxide in aquifers and to disposal of nuclear waste in unsaturated fractured Porous media.

Shaun D Fitzgerald - One of the best experts on this subject based on the ideXlab platform.

  • The vaporization of a liquid front moving through a hot Porous Rock. Part 2. Slow injection
    Journal of Fluid Mechanics, 1997
    Co-Authors: Andrew W Woods, Shaun D Fitzgerald
    Abstract:

    We present a series of similarity solutions to describe the temperature field as liquid spreads from a line source into a Porous Rock saturated with liquid of higher temperature. We identify slow and fast flow regimes. In the slow flow regime, the liquid is heated to the far-field temperature by conduction of heat from the far field. In the fast flow regime, there is negligible conduction of heat from the far field. Instead, the liquid is heated to the far-field temperature by cooling a region of the host Rock near the source, and an internal boundary layer develops within the newly injected liquid. We successfully test our quantitative theoretical predictions with a series of laboratory experiments in which water was injected into a consolidated bed of sand filled with liquid of different temperature. We extend our model to describe the vaporization of liquid as it spreads slowly from a central source into a superheated Porous Rock. A further family of similarity solutions shows that the rate of vaporization depends upon the injection rate as well as upon the initial superheat of the reservoir. For high injection rates, the liquid is typically heated to the interface temperature long before reaching the interface. The rate of vaporization then becomes independent of the initial liquid temperature, and depends mainly on the reservoir superheat. For lower injection rates, heat is conducted from ahead of the boiling front into the liquid. As a result, for progressively smaller injection rates, an increasing fraction of the liquid vaporizes, until virtually all the liquid boils, and only a very small liquid zone develops in the Rock. Again, we successfully test our theoretical predictions with a laboratory experiment in which liquid water was injected into a superheated layer of permeable sandstone.

  • the instability of a vaporization front in hot Porous Rock
    Nature, 1994
    Co-Authors: Shaun D Fitzgerald, Andrew W Woods
    Abstract:

    IN many geothermal systems, water migrates into vapour-dominated Porous Rock either through natural recharge or through forced injection of water from a well1–5. If the host Rock is initially very hot, then a fraction of this injected water vaporizes6,7; as the water injection rate increases, the fraction which vaporizes decreases7. For modelling purposes, it is generally assumed that liquid–vapour interfaces in hot Porous Rocks are planar and stable6,7. But we show here, both theoretically and experimentally, that if a sufficient fraction of the liquid vaporizes, the interface can become unstable. The resulting 'fingering' instability can itself be stabilized: at short wavelengths by thermal diffusion, and at long wavelengths by the pressure increase caused by the excess vaporization at the tips of the fingers. These liquid fingers migrate through the Porous Rock much more rapidly than does a planar liquid front, and could therefore limit the time during which vapour may be extracted for geothermal power applications. We suggest that an optimal water injection rate for geothermal energy production may be that for which the interface is just stable, thereby maximizing the fraction of liquid which vaporizes, while suppressing the fingering instability.

  • the vaporization of a liquid front moving through a hot Porous Rock
    Journal of Fluid Mechanics, 1993
    Co-Authors: Andrew W Woods, Shaun D Fitzgerald
    Abstract:

    We develop an analytical model to describe the generation of vapour as water moves through a hot Porous Rock, as occurs in hot, geothermal reservoirs. Typically the isotherms in the liquid lag behind the water-vapour interface and so water is supplied to the interface at the interface temperature. This temperature is lower than that in the Rock far ahead of the interface. Therefore, as the hot Porous Rock is invaded with water, it cools and the heat released is used to vaporize some of the water. At low injection rates, vapour formed from the injected liquid may readily move ahead of the advancing liquid-vapour interface and so the interfacial pressure remains close to that in the far field ahead of the interface. The mass fraction that vaporizes is then limited by the superheat of the Rock. For larger injection rates, the interfacial vapour pressure becomes considerably greater than that in the far field in order to drive the vapour ahead of the moving interface. As a result, the interfacial temperature increases. The associated reduction in the thermal energy available for vaporization results in a decrease in the mass fraction of vapour produced. Since the vapour is compressible, the motion of the vapour ahead of the interface is governed by a nonlinear diffusion equation. Therefore, the geometry of injection has an important effect upon the mass fraction of water that vaporizes. We show that with a constant supply of water from (i) a point source, the mass fraction of water which vaporizes increases towards the maximum permitted by the superheat of the Rock; (ii) a line source, a similarity solution exists in which the mass fraction vaporizing is constant; and (iii) a planar source, the liquid-vapour interface steadily translates through the Rock with a very small fraction of the injected water vaporizing.