Numerical simulation of the heat extraction in EGS with thermal-hydraulic-mechanical coupling method based on discrete fractures model

Sun, Zheng; Zhang, Xu; Xu, Yi; Ye, Jun; Wang, Haoxuan; Lv, Shuhuan; Sun, Zhi-lei; Huang, Yong; Cai, Mingyu; Huang, Xiaoxue

doi:10.1016/j.energy.2016.10.046

Cited by 316 publications

(94 citation statements)

References 20 publications

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“…The final governing equation describing fluid flow in porous media can be written as follows 39,51,52 where p, T, and ε V are the fluid pressure, fluid temperature, and pore volumetric strain in porous media, respectively; C 1m = m S l + (1 − m )S m represents the storage coefficient of porous media; C 2m = m m l + (1 − m ) m represents the thermal expansion coefficient of porous media; C 3m = m represents Biot's coefficient of porous media; m is the reservoir porosity; S l and S m represent the storage coefficients of the fluid and rock matrix, respectively; l and m represent the thermal expansion coefficients of the fluid and rock matrix, respectively; l and μ are the density and dynamic viscosity of the fluid, respectively; and k m is the pressure-dependent pore permeability. The final governing equation describing fluid flow in porous media can be written as follows 39,51,52 where p, T, and ε V are the fluid pressure, fluid temperature, and pore volumetric strain in porous media, respectively; C 1m = m S l + (1 − m )S m represents the storage coefficient of porous media; C 2m = m m l + (1 − m ) m represents the thermal expansion coefficient of porous media; C 3m = m represents Biot's coefficient of porous media; m is the reservoir porosity; S l and S m represent the storage coefficients of the fluid and rock matrix, respectively; l and m represent the thermal expansion coefficients of the fluid and rock matrix, respectively; l and μ are the density and dynamic viscosity of the fluid, respectively; and k m is the pressure-dependent pore permeability.…”

Section: Governing Equation For Mass Conservationmentioning

confidence: 99%

“…Numerous studies have demonstrated that the local thermal nonequilibrium (LTNE) theory is more appropriate if there is a rapid heat transport or a large temperature difference between the rock matrix and the flowing fluid. 13 Based on the dual porosity model 37 or the discrete fracture network model, [38][39][40][41][42][43] some studies have been conducted to analyze the heat extraction in 2D or 3D EGS. However, the mechanical effect was not incorporated into the above model.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Investigation on heat extraction characteristics in randomly fractured geothermal reservoirs considering thermo‐poroelastic effects

Han

Cheng

Gao

et al. 2019

Energy Science & Engineering

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A fully coupled thermal‐hydraulic‐mechanical (THM) model was developed to investigate the underlying response mechanisms during heat extraction in fractured geothermal reservoirs. The random fracture network in the stimulated zone was reproduced based on the fractal theory. The coupled model accounts for the dominant physical phenomena including (a) fluid flow, heat transport, and solid deformation in porous media and fractures; (b) local thermal nonequilibrium (LTNE) between rock matrix and flowing fluid; and (c) temperature‐dependent fluid thermodynamic properties and stress‐dependent pore and fracture permeability. The proposed model was validated by several analytic solutions. Sequentially, the evolution of pore pressure, equivalent temperature, effective stress, and reservoir permeability was analyzed. The sensitivity of the heat extraction performance to fracture network morphology was discussed. Results show that interconnected large‐scale fractures dominate mass and heat transport. Widely distributed small‐scale fractures contribute to the cooling of the heat rock mass along many flow paths in parallel. The change in effective stress associated with fully coupled thermo‐poroelastic effects may induce fracture shear dilation and pore expansion, resulting in an enhancement of the overall reservoir permeability. There is a significant temperature difference between the solid phase and the fluid phase in fractures, but not in porous media. It is more reasonable to use the LTNE theory to analyze the heat extraction of fractured geothermal reservoirs. The fracture network morphology has a profound effect on heat extraction efficiency and injectivity. Undeveloped fracture networks will result in a higher injection pressure, earlier thermal breakthrough, and shorter lifetime, but higher heat extraction ratio. Properly increasing the fracture density can delay the thermal breakthrough time, prolong the service life, and improve the injectivity. Fully connected fracture networks may result in thermal short‐circuiting and earlier thermal breakthrough. Generating a complex and scattered fracture network but without preferential channels is conducive to extracting more heat from geothermal reservoirs.

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Section: Governing Equation For Mass Conservationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation on heat extraction characteristics in randomly fractured geothermal reservoirs considering thermo‐poroelastic effects

Han

Cheng

Gao

et al. 2019

Energy Science & Engineering

View full text Add to dashboard Cite

show abstract

“…In order to examine the accuracy of the proposed model and its numerical implementation in the fracture, a 2D single fracture model is studied in our previous work [19].…”

Section: Computational Modelmentioning

confidence: 99%

“…The two-dimensional EGS thermal recovery process numerical model [19] is extended to three-dimensional space. Considering local thermal non-equilibrium, the model adopts two energy equations to respectively describe the temperature field in the rock matrix and the fluid existing in fractures, which can conveniently deal with the actual rock-fluid heat transfer during the heat recovery.…”

Section: Thm Coupled Modelmentioning

confidence: 99%

Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model

Sun

Xin

et al. 2018

Energies

Self Cite

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Abstract:The Enhanced Geothermal System (EGS) constructs an artificial thermal reservoir by hydraulic fracturing to extract heat economically from hot dry rock. As the core element of the EGS heat recovery process, mass and heat transfer of working fluid mainly occurs in fractures. Since the direction of the natural and induced fractures are generally perpendicular to the minimum principal stress in the formation, as an effective stimulation approach, horizontal well production could increase the contact area with the thermal reservoir significantly. In this paper, the thermal reservoir is developed by a dual horizontal well system and treated as a fractured porous medium composed of matrix rock and discrete fracture network. Using the local thermal non-equilibrium theory, a coupled THM mathematical model and an ideal 3D numerical model are established for the EGS heat extraction process. EGS heat extraction capacity is evaluated in the light of thermal recovery lifespan, average outlet temperature, heat production, electricity generation, energy efficiency and thermal recovery rate. The results show that with certain reservoir and production parameters, the heat production, electricity generation and thermal recovery lifespan can achieve the commercial goal of the dual horizontal well system, but the energy efficiency and overall thermal recovery rate are still at low levels. At last, this paper puts forward a series of optimizations to improve the heat extraction capacity, including production conditions and thermal reservoir construction design.

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“…Fluid flow in fracture networks that are constituted by individual fractures in reservoir rocks is encountered in different areas, such as enhanced oil and gas recovery, geothermal reservoir exploitation, geological sequestration of carbon dioxide, and water resources exploitation [1][2][3][4]. Therefore, the understanding of fluid flow in a fracture is of crucial importance for modeling flow in more complex fracture networks.…”

Section: Introductionmentioning

confidence: 99%

Laboratory Investigation of Flow Paths in 3D Self-Affine Fractures with Lattice Boltzmann Simulations

Cherubini

Galindo‐Torres

et al. 2018

Energies

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Abstract:In this study, laboratory experiments and simulations have been conducted to investigate single water phase flow through self-affine rough fractures. It is the first time that 3D printing technology is proposed for the application of generating self-affine rough fractures. The experimental setup was designed to measure the water volume by dividing the discharging surface into five sections with equal distances under constant injection flow rates. Water flow through self-affine rough fractures was simulated numerically by using the Lattice Boltzmann method (LBM). An agreement between the experimental data and the numerical simulation results was achieved. The fractal dimension is positively correlated to fracture surface roughness and the fracture inclination represents the gravity force acting on the water flow. The influences of fracture inclinations, fractal dimensions, and mismatch wavelengths were studied and analyzed, with an emphasis on flow paths through a self-affine rough fracture. Different values of fractal dimensions, fracture inclinations, and mismatch wavelengths result in small changes of flow rates from five sections of discharging surface. However, the section of discharging surface with the largest flow rate remains constant. In addition, it is found that the gravity force can affect flow paths. Combined with the experimental data, the simulation results are used to explain the preferential flow paths through fracture rough surfaces from a new perspective. The results may enhance our understanding of fluid flow through fractures and provide a solid background for further research in the areas of energy exploration and production.

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Numerical simulation of the heat extraction in EGS with thermal-hydraulic-mechanical coupling method based on discrete fractures model

Cited by 316 publications

References 20 publications

Investigation on heat extraction characteristics in randomly fractured geothermal reservoirs considering thermo‐poroelastic effects

Investigation on heat extraction characteristics in randomly fractured geothermal reservoirs considering thermo‐poroelastic effects

Numerical Investigation on the Heat Extraction Capacity of Dual Horizontal Wells in Enhanced Geothermal Systems Based on the 3-D THM Model

Laboratory Investigation of Flow Paths in 3D Self-Affine Fractures with Lattice Boltzmann Simulations

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