A three-dimensional thermo-hydro-mechanical coupled model for enhanced geothermal systems (EGS) embedded with discrete fracture networks

Wang, Yang; Li, Tuo; Chen, Yun; Ma, Guowei

doi:10.1016/j.cma.2019.06.037

Cited by 67 publications

(21 citation statements)

References 59 publications

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“…Second, we implement mechanical effects within a 3D TH model of the Pontgibaud CFZ, with the unique objective of questioning consistency of the obtained results with field data. To our knowledge, THM models are generally applied to purely pressure-driven flow, where fluid density is constant and thus with no buoyancy-driven components (see, however, [54,55]). However, Vallier et al [24] used a similar approach as ours but with another objective being the study of mechanical effects on gravity anomalies, so that no information on the coupling between fluid flow and mechanical effects can be retrieved.…”

Section: Introductionmentioning

confidence: 99%

Crustal Fault Zones (CFZ) as Geothermal Power Systems: A Preliminary 3D THM Model Constrained by a Multidisciplinary Approach

et al. 2021

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The Pontgibaud crustal fault zone (CFZ) in the French Massif Central provides an opportunity to evaluate the high-temperature geothermal potential of these naturally permeable zones. Previous 2D modeling of heat and mass transfer in a fault zone highlighted that a subvertical CFZ concentrates the highest temperature anomalies at shallow depths. By comparing the results of these large-scale 2D numerical models with field data, the depth of the 150°C isotherm was estimated to be at a depth of 2.5 km. However, these results did not consider 3D effects and interactions between fluids, deformation, and temperature. Here, field measurements are used to control the 3D geometry of the geological structures. New 2D (thin-section) and 3D (X-ray microtomography) observations point to a well-defined spatial propagation of fractures and voids, exhibiting the same fracture architecture at different scales (2.5 μm to 2 mm). Moreover, new measurements on porosity and permeability confirm that the highly fractured and altered samples are characterized by large permeability values, one of them reaching 10-12 m2. Based on a thermoporoelastic hypothesis, a preliminary 3D THM numerical model is presented. A first parametric study highlights the role of permeability, stress direction, and intensity on fluid flow. In particular, three different convective patterns have been identified (finger-like, blob-like, and double-like convective patterns). The results suggest that vertical deformation zones oriented at 30 and 70° with respect to the maximum horizontal stress direction would correspond to the potential target for high-temperature anomalies. Finally, a large-scale 3D numerical model of the Pontgibaud CFZ, based on THM coupling and the comparison with field data (temperature, heat flux, and electrical resistivity), allows us to explore the spatial geometry of the 150°C isotherm. Although simplified hypotheses have been used, 3D field data have been reproduced.

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Section: Introductionmentioning

confidence: 99%

Crustal Fault Zones (CFZ) as Geothermal Power Systems: A Preliminary 3D THM Model Constrained by a Multidisciplinary Approach

et al. 2021

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“…Considering thermal dilatation of gas and coal, thermal convection, thermal conduction, and gas adsorption energy, the governing equation for heat transfer can be described as [29] ∂…”

Section: Heat Transfer Equationsmentioning

confidence: 99%

Numerical Simulation of Coupled Thermal-Hydrological-Mechanical-Chemical Processes in the Spontaneous Combustion of Underground Coal Seams

Liang

Zhou

2021

Geofluids

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In this study, we develop a fully coupled thermal-hydrological-mechanical-chemical (THMC) model to analyze the spontaneous combustion process of underground coal seams, focusing on investigating the influences of the pressure difference between oxygen and coal, the rate of coal-oxygen reaction heat, and the activation energy. The simulation results show that as oxygen propagates into the coal seams, the coal-oxygen reaction causes the spontaneous combustion of coal to heat. The consumption of oxygen leads to an increase in oxygen consumption along the way and a decrease in gas pressure. The permeability near the right boundary increases while significantly reducing the area far away from the right boundary as the predominant effect of spontaneous combustion. Additionally, a sensitivity study shows that a more considerable pressure difference and coal-oxygen reaction heat contribute to promoting the coal temperature, while the activation energy has a slight effect. Moreover, an increase in coal-oxygen reaction heat and activation energy accelerates the oxygen consumption rate and thus causes a lower oxygen concentration. Overall, the results provide a basis for the prediction and prevention of coal seam spontaneous combustion.

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“…Yet, explicitly accounting for fractures in numerical models of poromechanical problems is a challenging task and often comes at the expenses of a very high computational cost (Lei et al., 2017; McDermott & Kolditz, 2006; Pandey et al., 2017; Salimzadeh et al., 2018; Thomas et al., 2020; Yoshioka et al., 2019). In order to facilitate the calculation for large problems, dense fractured networks are often simplified as equivalent porous media, like the ubiquitous joint model, and computational resources are used for other purposes, such as reactive transport, phase changes, and dynamics or complex plasticity models (e.g., Birdsell et al., 2018; Liu et al., 2009; Parisio, Vilarrasa, et al., 2019; Rinaldi et al., 2015; Rutqvist, Wu, et al., 2002; Rutqvist et al., 2005; Taron & Elsworth, 2009; Vallier et al., 2020; Y. Wang et al., 2019).…”

Section: Introductionmentioning

confidence: 99%

How Equivalent Are Equivalent Porous Media?

Zareidarmiyan

Parisio

Makhnenko

et al. 2021

Geophysical Research Letters

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Fractures are ubiquitous in rock masses and control their transport and deformation properties (Cornet, 2015;Jaeger et al., 2007). On the one hand, fractures represent preferential paths for fluid flow because their permeability is usually several orders of magnitude higher than that of intact rock (Rutqvist, 2015;Witherspoon et al., 1980;Zimmerman & Bodvarsson, 1996). On the other hand, fractures represent weak planes with lower strength and higher deformability than the intact rock (Bandis et al., 1983;Barton, 1976). The hydraulic and mechanical responses of fractured media are strongly coupled, meaning that the deformation induced by pore pressure changes causes permeability changes as a result of fracture opening or closure, which in turn affects the pore pressure (

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A three-dimensional thermo-hydro-mechanical coupled model for enhanced geothermal systems (EGS) embedded with discrete fracture networks

Cited by 67 publications

References 59 publications

Crustal Fault Zones (CFZ) as Geothermal Power Systems: A Preliminary 3D THM Model Constrained by a Multidisciplinary Approach

Crustal Fault Zones (CFZ) as Geothermal Power Systems: A Preliminary 3D THM Model Constrained by a Multidisciplinary Approach

Numerical Simulation of Coupled Thermal-Hydrological-Mechanical-Chemical Processes in the Spontaneous Combustion of Underground Coal Seams

How Equivalent Are Equivalent Porous Media?

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