The Experts below are selected from a list of 285 Experts worldwide ranked by ideXlab platform
Huidong Wang - One of the best experts on this subject based on the ideXlab platform.
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heat extraction mechanism in a Geothermal Reservoir with rough walled fracture networks
International Journal of Heat and Mass Transfer, 2018Co-Authors: Yun Chen, Huidong WangAbstract:Abstract This study aims at understanding the mechanism of heat extraction from a Geothermal Reservoir characterized by rough-walled fracture networks. A unified pipe-network method (UPM) which simplifies both fractures and the rock matrix as pipes is developed considering the local thermal non-equilibrium (LTNE) theory, and it is verified against an analytical solution. Three-dimensional simulations of macroscopic fluid flow and heat transfer in a fractured Geothermal Reservoir are conducted to take account of fracture roughness. The channeling effect and the heterogeneous distribution of fluid temperature in a core-scale model with a rough-walled fracture surface are simulated. An equivalent heat transfer coefficient (EHTC) is obtained from numerical experiments with respect to the flow rate, mechanical aperture and the equivalent hydraulic aperture. A representative element volume is then used to investigate the flow and heat transfer process in a Geothermal Reservoir with rough-walled fracture networks by applying the obtained EHTC. Results demonstrate that it is essential to use the proposed EHTC since the constant heat transfer coefficient (HTC) recommended in previous studies underestimates the final outlet fluid temperature in cases with rough-walled fractures.
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the simulation of thermo hydro chemical coupled heat extraction process in fractured Geothermal Reservoir
Applied Thermal Engineering, 2018Co-Authors: Yun Chen, Huidong WangAbstract:Abstract Chemical reaction effect is a critical issue in the heat extraction process of a fractured Geothermal Reservoir. In this study, the thermo-hydro-chemical coupled condition is simulated based on a unified pipe-network method (UPM) by considering interconnected fracture networks embedded in the rock mass. The chemical reaction kinetics of silica precipitation and dissolution is incorporated to capture and examine the effects of the silica-water interaction on the evolution of fracture apertures. The chemical influenced heat transfer between solid and fluid phases in the fractured porous media is characterized by a local thermal non-equilibrium (LTNE) model introduced based on two energy balance equations. A pipe equivalent technique is used to discretize the multiphysical coupled equations and unify the fracture-matrix information at the interface through the superposition principle in the UPM framework. Convergence tests are performed to verify the proposed model with one large fracture embedded in a doublet system for Geothermal development. Fracture networks are then introduced in a case study where the influences of different injection temperature, saturation condition, injection pressure differential and initial fracture aperture on the silica reaction related alteration of fracture apertures as well as the heat production are analyzed.
Yun Chen - One of the best experts on this subject based on the ideXlab platform.
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heat extraction mechanism in a Geothermal Reservoir with rough walled fracture networks
International Journal of Heat and Mass Transfer, 2018Co-Authors: Yun Chen, Huidong WangAbstract:Abstract This study aims at understanding the mechanism of heat extraction from a Geothermal Reservoir characterized by rough-walled fracture networks. A unified pipe-network method (UPM) which simplifies both fractures and the rock matrix as pipes is developed considering the local thermal non-equilibrium (LTNE) theory, and it is verified against an analytical solution. Three-dimensional simulations of macroscopic fluid flow and heat transfer in a fractured Geothermal Reservoir are conducted to take account of fracture roughness. The channeling effect and the heterogeneous distribution of fluid temperature in a core-scale model with a rough-walled fracture surface are simulated. An equivalent heat transfer coefficient (EHTC) is obtained from numerical experiments with respect to the flow rate, mechanical aperture and the equivalent hydraulic aperture. A representative element volume is then used to investigate the flow and heat transfer process in a Geothermal Reservoir with rough-walled fracture networks by applying the obtained EHTC. Results demonstrate that it is essential to use the proposed EHTC since the constant heat transfer coefficient (HTC) recommended in previous studies underestimates the final outlet fluid temperature in cases with rough-walled fractures.
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the simulation of thermo hydro chemical coupled heat extraction process in fractured Geothermal Reservoir
Applied Thermal Engineering, 2018Co-Authors: Yun Chen, Huidong WangAbstract:Abstract Chemical reaction effect is a critical issue in the heat extraction process of a fractured Geothermal Reservoir. In this study, the thermo-hydro-chemical coupled condition is simulated based on a unified pipe-network method (UPM) by considering interconnected fracture networks embedded in the rock mass. The chemical reaction kinetics of silica precipitation and dissolution is incorporated to capture and examine the effects of the silica-water interaction on the evolution of fracture apertures. The chemical influenced heat transfer between solid and fluid phases in the fractured porous media is characterized by a local thermal non-equilibrium (LTNE) model introduced based on two energy balance equations. A pipe equivalent technique is used to discretize the multiphysical coupled equations and unify the fracture-matrix information at the interface through the superposition principle in the UPM framework. Convergence tests are performed to verify the proposed model with one large fracture embedded in a doublet system for Geothermal development. Fracture networks are then introduced in a case study where the influences of different injection temperature, saturation condition, injection pressure differential and initial fracture aperture on the silica reaction related alteration of fracture apertures as well as the heat production are analyzed.
Ahmad Ghassemi - One of the best experts on this subject based on the ideXlab platform.
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a reactive thermo poroelastic analysis of water injection into an enhanced Geothermal Reservoir
Geothermics, 2014Co-Authors: Chakra Rawal, Ahmad GhassemiAbstract:Abstract Coupled thermo-poro-chemo-mechanical processes in Geothermal systems impact the Reservoir response during injection and production procedures by affecting fracture permeability. A three-dimensional numerical model is presented to analyze these processes during fluid injection into Geothermal Reservoirs. The solid mechanics aspect of the problem is computed using the displacement discontinuity boundary element method (BEM) while transport processes within the facture are modeled using the finite element method (FEM). The FEM and BEM formulations are integrated to set up a system of equations for unknown temperature, pressure, concentration, and fracture aperture. The fluid diffusion, heat conduction and solute diffusion in the Reservoir are treated using BEM so that the need of infinite Reservoir domain discretization is eliminated. The numerical model is used to analyze the fracture response to non-isothermal reactive flow in EGS. Numerical examples of SiO 2 undersaturated-cold water injection into the Geothermal Reservoir show that silica dissolves from the rock matrix, increasing the fracture aperture. The zone of silica dissolution spreads into the fracture with continuous fluid injection. At large injection times, thermoelastic stress has a greater impact on fracture aperture compared to poroelastic stress. Simulations that consider natural fracture stiffness heterogeneity show the development of a non-uniform flow path within the crack, with lower rock matrix cooling and thus enhanced silica reactivity in the high stiffness regions. As a result, areas of higher joint normal stiffness show lower aperture increases in response to the thermo-poroelastic processes, but a higher aperture expansion due to silica dissolution. Depending on the injectate saturation state with respect to quartz, silica is added or removed from the rock matrix. This process is likely to impact the rock matrix properties and its mechanical response to stress perturbations associated with fluid circulation.
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a review of some rock mechanics issues in Geothermal Reservoir development
Geotechnical and Geological Engineering, 2012Co-Authors: Ahmad GhassemiAbstract:Rock mechanics and geomechanical studies can provide crucial information for economic Geothermal Reservoir development. Although significant progress has been made in Reservoir geomechanics, technical challenges specific to the Geothermal area (high temps, data collection, experimentation issues) have prevented widespread use of geomechanics in Geothermal Reservoir development. However, as the Geothermal industry moves to develop more challenging resources using the concept of enhanced Geothermal systems (EGS), and to maximize productivity from conventional resources, the need for improved understanding of geomechanical issues and developing specific technologies for Geothermal Reservoirs has become critical. Rock mechanics research and improved technologies can impact areas related to in-situ stress characterization, initiation and propagation of artificial and natural fractures, and the effects of coupled hydro-thermo-chemo-mechanical processes on fracture permeability and induced seismicity. Rock mechanics/geomechanics research, including experimental and theoretical investigations as well as numerical and analytical solutions, has an important role in optimizing Reservoir design and heat extraction strategies for sustainable Geothermal energy development. A number of major areas where rock mechanics research can facilitate Geothermal systems development are reviewed in this paper with particular emphasis on EGS design and management.
Scott W Phillips - One of the best experts on this subject based on the ideXlab platform.
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precise microearthquake locations and fluid flow in the Geothermal Reservoir at soultz sous forets france
Bulletin of the Seismological Society of America, 2000Co-Authors: Scott W PhillipsAbstract:I relocated two microearthquake clusters induced by hydraulic stimulation of a hot-dry-rock Geothermal Reservoir in the Rhine Graben near Soultz-sous-Forets, France. The two clusters were chosen from a collection of clusters identified within a 16,000-event data set obtained in 1993. I determined P - and S -wave arrival times, manually, choosing distinctive peaks if waveforms were similar at a given station, or first breaks if waveforms were emergent or nodal, judging weights accordingly. Requiring a minimum of five arrival times yielded populous clusters of 226 and 355 events. In both cases, relocation revealed two distinct planar patches of activity, 100 to 200 m across, intersecting and truncating one another along a common edge. Linear segments traverse the planar patches and may mark intersections with seismically inactive fractures. The earliest activity occurred along these segments. These segments may therefore mark permeable zones that could be important components of the fluid-flow network. The interpretation of linear segments as flow paths is supported by path dimension constraints derived from fluid-flow modeling studies and by the expected confining effects of hydrothermal sealing found in cored fractures. Orientations of the planar features are verified through consistency with orientations found in core and logging studies. In addition, focal mechanisms obtained by constraining slip planes parallel to active planes indicate normal to right-lateral strike slip, consistent with the measured stress field. Focal mechanisms indicate mass deficits at inside corners, implying that the concentrations of activity at fracture intersections may result from slip on one fracture causing extension and a resulting permeability increase in the other. The improved location precision results from a ten-fold improvement in the precision of arrival-time estimation for phases that were similar, as estimated from the standard deviation of residuals, grouped by station and phase, before and after repicking. Only a two-fold improvement was noted for poorly correlated or nodal phases. For this data set, the manual phase picking yielded more interpretable detail in the location patterns, compared to results of an automatic, cross-correlation technique. The manual results could be used to guide improvements to automatic techniques to obtain precise locations of the entire data set.
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detailed joint structure in a Geothermal Reservoir from studies of induced microearthquake clusters
Journal of Geophysical Research, 1997Co-Authors: Scott W Phillips, Leigh House, Michael FehlerAbstract:Microearthquake clusters form distinct, planar patterns within five study regions of a Geothermal Reservoir undergoing hydraulic fracturing at Fenton Hill, New Mexico. The patterns define individual, slipping joint surfaces of dimension 40–120 m, containing 80–150 events each. Sharp, straight edges truncate the clusters; we interpret these as marking intersections with aseismic joints. Each edge orientation is consistent with an intersection between the active joint and a plane oriented parallel to one of the other clusters we identify. Therefore it appears that cluster shapes constrain the geometry of seismic and aseismic joints; both could be important components of the fluid-flow network. The distribution of inferred slip plane orientations is consistent with but fails to provide sufficient constraint to differentiate conclusively between two, very different, stress field estimates, one measured using pressurization and wellbore breakouts, the other using focal mechanisms of the largest microearthquakes. An impermeable joint model, requiring pore pressure in excess of the normal stress on a joint before slip can occur, was inconsistent with many of the inferred slip plane orientations. The high-quality locations were possible because events from the same cluster generated nearly similar waveforms, permitting the precise determination of relative arrival times. Standard deviations of arrival-time residuals fall between 0.1 and 1.1 ms for these clusters. Major axes and aspect ratios of the 90% confidence ellipsoids range from 6 to 28 m and 1.5 to 8, respectively. Small events dominate the seismic energy release and thoroughly populate the identified, active joints, allowing the hypocenters to reflect details of the joint structure. To further investigate the Reservoir structure, we applied a source-array, slant-stack technique to waveforms from the well-located clusters, yielding directions that scattered energy left each cluster. By studying paths of scattered waves we expected to pinpoint impedance contrasts that might have indicated concentrations of fluid-filled joints. However, results show that scattered energy in the S wave coda left the source region in the same direction as the direct S wave. Direct waves may have excited borehole tube waves that became trapped in the vicinity of the geophone tool, overwhelming any energy scattered from the Reservoir.
Benoit Gibert - One of the best experts on this subject based on the ideXlab platform.
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high temperature instruments and methods developed for supercritical Geothermal Reservoir characterisation and exploitation the hiti project
Geothermics, 2014Co-Authors: Ragnar Asmundsson, Jan Henninges, Philippe A Pezard, Bernard Sanjuan, Jeanluc Deltombe, Nigel Halladay, Francois Lebert, Alain Gadalia, Romain Millot, Benoit GibertAbstract:During the early years of the Iceland Deep Drilling Project (IDDP), development of three distinctive technological and scientific approaches were formalised and then carried out until 2010 within a European funded project called HiTI (high temperature instruments for supercritical Geothermal Reservoir characterisation and exploitation). These approaches were: (1) development of several downhole instruments allowing them to function up to 300 ◦C and 400 ◦C, (2) identification of two new Na/Li cation ratio geothermometric relationships valid at very high temperature, (3) tracer testing with high temperature tolerant organic isomers and finally and (4) basalt rock deformation and petrophysical properties laboratory investigations at high temperature and pressure conditions.