The Experts below are selected from a list of 51918 Experts worldwide ranked by ideXlab platform
Olaf Kolditz - One of the best experts on this subject based on the ideXlab platform.
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simulation of heat extraction from crystalline rocks the influence of coupled processes on differential reservoir cooling
Geothermics, 2006Co-Authors: Christopher Mcdermott, Helmut Tenzer, Andreas R L Randriamanjatosoa, Olaf KolditzAbstract:Abstract Processes operating during the extraction of heat from Fractured rocks influence dynamically their fluid flow and heat transport characteristics. The incorporation of pressure- and temperature-dependent rock parameters, coupled with geomechanical Deformation, is particularly important for predictive modelling of geothermal reservoirs hosted in crystalline rock masses. Changes in flow and transport parameters of Fractures caused by variations in local effective stress are computed using an experimentally validated geomechanical model [McDermott, C.I., Kolditz, O., 2006. Geomechanical model for Fracture Deformation under hydraulic, mechanical and thermal loads. Hydrogeol. J. 14, 487–498]. Local effective stress changes are linked to alterations in reservoir fluid pressures, and to in situ stress conditions, including the build-up of thermal stresses resulting from the cooling of the rock mass. These processes are simulated using a finite-element model in order to study the behaviour of the Spa Urach (southwestern Germany) potential geothermal reservoir. The model couples mechanical Deformation and alteration of Fracture parameters with pressure-, temperature- and salinity-dependent fluid parameter functions. The effects of potential reservoir damage on reservoir productivity are investigated to help identify optimal heat recovery schemes for the long-term economical exploitation of geothermal systems. Simulation results indicate that preferential fluid flow paths and shortcuts may develop, depending on the mechanical and thermal stress releases that occur during intense exploitation of these systems.
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geomechanical model for Fracture Deformation under hydraulic mechanical and thermal loads
Hydrogeology Journal, 2006Co-Authors: Christoper Mcdermott, Olaf KolditzAbstract:Hydraulic flow and transport (heat and solute) within crystalline rocks is dominated by the Fracture systems found within them. In situ stress conditions have a significant impact on the hydraulic, mechanical and thermal coupled processes, and quantification of these processes provides a key to understanding the often transient time-dependent behaviour of crystalline rocks. In this paper, a geomechanical model is presented which describes Fracture closure as a function of effective stress and the changes in parameters such as storage, permeability, porosity and aperture. Allowing the Fracture closure to be defined by the change in normal effective stress provides a link to the numerical consideration of parametrical changes due to rock stress alterations caused for example by changes in Fracture fluid pressure, stress release, tectonic stress, thermal stress, orientation of the natural Fracture in the pervasive stress system and local changes in a rock mass due to stress alteration. The model uses geometrical considerations based on a fractal distribution of apertures on the Fracture surface, and applies well-established analytical elastic Deformation solutions to calculate the Deformation response to changes in effective stress. Analysis of the fractal generation method allows a standard normal distribution of Fracture apertures to be predicted for all common fractal dimensions relating to a 2D surface. Changes in the Fracture aperture are related to hydraulic functions such as permeability, storage and porosity of the Fracture. The geomechanical model is experimentally validated against laboratory scale experimental data gained from the closure of a Fractured sample recovered at a depth of 3,800 m from the KTB pilot borehole. Parameters for matching the experimental data were established externally, the only fitting parameters applied were the minimum and maximum contact area between the surfaces and the number of allowable contacts. The model provides an insight into the key processes determining the closure of a Fracture, and can act as a material input function for numerical models linking the effects of changes in the stress field, hydraulic or thermal conditions, to the flow and transport parameters of a Fractured system.
Yuan Wang - One of the best experts on this subject based on the ideXlab platform.
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a numerical manifold method model for analyzing fully coupled hydro mechanical processes in porous rock masses with discrete Fractures
Advances in Water Resources, 2017Co-Authors: Mengsu Hu, Jonny Rutqvist, Yuan WangAbstract: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.
Luis E Zerpa - One of the best experts on this subject based on the ideXlab platform.
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A semi-analytical correlation of thermal-hydraulic-mechanical behavior of Fractures and its application to modeling reservoir scale cold water injection problems in enhanced geothermal reservoirs
Geothermics, 2016Co-Authors: Shihao Wang, Philip H. Winterfeld, Yu-shu Wu, Zhaoqin Huang, Luis E ZerpaAbstract:Fractured enhanced geothermal system (EGS) reservoirs are typically sensitive to thermal and mechanical change induced by cold water injection. It has been observed that the permeability at the cold water injector is significantly enhanced. The physical thermal-hydrologic-mechanic (THM) process behind this phenomenon is that, the injection of cold water decreases the temperature of the reservoir rock and causes the matrix block to shrink, resulting in an increase of the Fracture aperture and Fracture permeability. Therefore, it is of great importance to quantify the effect of thermally induced Fracture aperture change to better predict the behavior/performance of EGS reservoirs.In this work, we develop a novel correlation of the thermal-induced normal change of Fracture aperture. The new correlation is based on the analytical solution of the governing displacement equations. Compared to the existing empirical correlations, the new correlation can better describe the physical processes by including the thermal effect on the matrix-Fracture Deformation. We have verified this correlation with respect to refined simulation results and implemented this correlation in a fully coupled massively parallel geothermal simulator, THM-EGS. We have applied this correlation to study field scale problems with certain parameters from Habanero Field in Copper Basin, Australia. Our results demonstrate that the Fracture permeability near the cold water injector could be enhanced 7 times.
Mengsu Hu - One of the best experts on this subject based on the ideXlab platform.
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a numerical manifold method model for analyzing fully coupled hydro mechanical processes in porous rock masses with discrete Fractures
Advances in Water Resources, 2017Co-Authors: Mengsu Hu, Jonny Rutqvist, Yuan WangAbstract: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.
Ahmad Ghassemi - One of the best experts on this subject based on the ideXlab platform.
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3d thermo poroelastic analysis of Fracture network Deformation and induced micro seismicity in enhanced geothermal systems
Geothermics, 2015Co-Authors: Reza Safari, Ahmad GhassemiAbstract:Abstract This study considers three-dimensional (3D) analyses of a Fracture network in an enhanced geothermal system (EGS) with special emphasis on the role of coupled thermo-hydro-mechanical processes and Fractures mechanical interactions. The behavior of the system is modeled by coupling a thermo-poroelastic displacement discontinuity (DD) method (for Fracture opening and ride, fluid and heat diffusion in the reservoir matrix) with a finite element method for the fluid and heat convection and conduction inside the Fractures. The nonlinear characteristics of the Fracture Deformation in the normal (change of Fracture status from joint Fracture to hydraulic Fracture) and shear Deformation (change of Fracture status from stick to slip) are taken into account. The resulting method is then used to simulate relatively short term injection/extraction processes into/from a synthetic Fracture network consisting of a major Fracture intersected by a set of smaller natural Fractures. Injection/extraction into/from the Fracture network results in gradual shearing of the Fractures that impact the thermo-hydro-mechanical characteristics of the Fracture system. It is also shown that the early micro-seismic events are associated with Fracture slip on connected Fractures due to thermal perturbation. Also, continued injection leads to stress intensity conditions favorable for Fracture propagation in shear and tensile modes which could increase reservoir surface area and further contribute to seismicity.
