Numerical simulation of the heat extraction in 3D-EGS with thermal-hydraulic-mechanical coupling method based on discrete fractures model

Yao, Jun; Xu, Zaiyan; Sun, Zheng; Huang, Zhaoqin; Liu, Junrong; Li, Yang; Xin, Ying; Yan, Xiangqiao; Liu, Wenzheng

doi:10.1016/j.geothermics.2017.12.005

Cited by 209 publications

(68 citation statements)

References 25 publications

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“…This makes sense because the injected low-temperature fluid can induce thermal stress and pore pressure, resulting in an increase in the effective stress (note that tension is positive; see Figure 13). The change in injection pressure is similar to the result of Yao et al 40 When considering the thermo-poroelastic effect, the change in the fracture aperture at the injection point is more significant. Meanwhile, the decrease in the mean effective pressure (note that compression is positive) will result in the permeability Conversely, it can also be seen that at the early stage, a slight decrease in permeability occurs near the production well due to fluid extraction.…”

Section: Evolution Of Permeabilitysupporting

confidence: 85%

“…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%

“…For external boundaries: (a) The pore pressure obeys the Dirichlet boundary condition with p out = 24 MPa; (b) the displacement is constrained in all normal directions; (c) Unlike the published models,[38][39][40][41][42][43] an open boundary condition for modeling heat flux across the boundary is defined as T = T out , if n · Q < 0 (inflow), otherwise -n · q = 0, if n · Q ≥ 0 (outflow). To reveal the stress sensitivity of reservoir permeability, the effect of in situ stresses should be incorporated into the model.…”

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confidence: 99%

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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: Evolution Of Permeabilitysupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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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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“…Heat mining and CO 2 sequestration in deep thermal reservoirs involve coupled processes from physical to geo‐mechanical process. Various models of thermo‐hydro (TH), hydro‐mechanical (HM) and thermo‐hydro‐mechanical (THM) describing the coupled quantities were extensively studied . Depending on the amount and content of the rock‐forming mineral, the rock effective strength is affected under pore‐pressure or external stress influence, which further affects the fluid flow and rock deformation degree .…”

Section: Introductionmentioning

confidence: 99%

“…The pressure alternation methods aims at increasing CO 2 sequestration while maintaining a significant heat production from the fractured geothermal reservoir. The pressure alternation scheme is applied to 3D geometric EGS reservoir with doublet well system consisting of multiple intersecting fractures to mimic a real fractured geothermal reservoir . Various parameters related to CO 2 sequestration and geothermal heat mining were analyzed.…”

Section: Introductionmentioning

confidence: 99%

Combination of double and single cyclic pressure alternation technique to increase CO ₂ sequestration with heat mining in enhanced geothermal reservoirs by thermo‐hydro‐mechanical coupling method

Sun

Bongole

et al. 2020

Int J Energy Res

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Summary The rise in global temperature due to an unceasingly increase in non‐condensable gases (NCG) prompts more development of safe and economical CCUS (Carbon Capture Utilization and Storage) technologies. Carbon dioxide (CO2) sequestration with heat mining in deep enhanced geothermal systems (EGSs) is one of the promising methods to reduce CO2 emitted to the atmosphere. In this study, a cyclic alternation of pressures at the injection and production wells is applied in an EGS for heat mining together with CO2 deposit. Simultaneous alternation of the injection and production pressures can significantly increase the amount of CO2 sequestrated compared to applying a fixed pumping or withdrawing pressures at the injector and producer respectively. At the injection well, alternation in pumping pressures at high frequency (small interval of days) increased CO2 sequestration rate. Reducing the pumping frequency resulted in the lowering of the total amount of CO2 sequestrated, lesser than using a fixed pumping pressure. The alternation in pumping frequency has a direct relationship to the CO2 sequestration rate. The frequency of the injection and production pressures refers to the interval in days of the interchange in pressure between high to a low value and vice‐versa. Furthermore, simultaneous alternation of pressures at the injection and production wells respectively (double cyclic method) improved geothermal heat extraction efficiency, thus higher performance for both geothermal and CO2 sequestration projects.

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The role of temperature‐enhanced fault closure in promoting postinjection pressure diffusion and seismicity in enhanced geothermal systems

Ji,

Chen,

Hofmann

et al. 2023

Deep Underground Science and Engineering

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Post shut‐in seismic events in enhanced geothermal systems (EGSs) occur predominantly at the outer rim of the co‐injection seismic cloud. The concept of postinjection fracture and fault closure near the injection well has been proposed and validated as a mechanism for enhancing post shut‐in pressure diffusion that promotes seismic hazard. This phenomenon is primarily attributed to the poro‐elastic closure of fractures resulting from the reduction of wellbore pressure after injection termination. However, the thermal effects in EGSs, mainly including heat transfer and thermal stress, may not be trivial and their role in postinjection fault closure and pressure evolution needs to be explored. In this study, we performed numerical simulations to analyze the relative importance of poro‐elasticity, heat transfer, and thermo‐elasticity in promoting postinjection fault closure and pressure diffusion. The numerical model was first validated against analytical solutions in terms of fluid pressure diffusion and against heated flow‐through experiments in terms of thermal processes. We then quantified and distinguished the contribution of each individual mechanism by comparing four different shut‐in scenarios simulated under different coupled conditions. Our results highlight the importance of poro‐elastic fault closure in promoting postinjection pressure buildup and seismicity, and suggest that heat transfer can further augment the fault closure‐induced pressure increase and thus potentially intensify the postinjection seismic hazard, with minimal contribution from thermo‐elasticity.

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Numerical simulation of the heat extraction in 3D-EGS with thermal-hydraulic-mechanical coupling method based on discrete fractures model

Cited by 209 publications

References 25 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

Combination of double and single cyclic pressure alternation technique to increase CO ₂ sequestration with heat mining in enhanced geothermal reservoirs by thermo‐hydro‐mechanical coupling method

The role of temperature‐enhanced fault closure in promoting postinjection pressure diffusion and seismicity in enhanced geothermal systems

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Numerical simulation of the heat extraction in 3D-EGS with thermal-hydraulic-mechanical coupling method based on discrete fractures model

Cited by 209 publications

References 25 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

Combination of double and single cyclic pressure alternation technique to increase CO 2 sequestration with heat mining in enhanced geothermal reservoirs by thermo‐hydro‐mechanical coupling method

The role of temperature‐enhanced fault closure in promoting postinjection pressure diffusion and seismicity in enhanced geothermal systems

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Combination of double and single cyclic pressure alternation technique to increase CO ₂ sequestration with heat mining in enhanced geothermal reservoirs by thermo‐hydro‐mechanical coupling method