Numerical Research of Thermo–Hydro–Mechanical Response and Heat Transfer in a Multiwell EGS with Rough-Walled Fractures after Shear Deformation
Publication: International Journal of Geomechanics
Volume 24, Issue 1
Abstract
Natural fractures may not be developed in hot dry rock reservoirs, and tectonism or fracturing can induce the shear deformation of fractures and result in large-scale rough-walled fractures. Previous studies usually ignore the effect of rough walls on production performance. This study constructs a 3D multiwell enhanced geothermal system (EGS) model with two rough-walled fractures after shear deformation, systematically investigates the response characteristics of each physical field under the thermo–hydro–mechanical coupling, and determines the effect of the distribution of two rough-walled fractures and the relationship between the well layout scheme and the shear deformation direction on the production performance. The obtained results indicate that the distribution and evolution of the temperature and seepage fields are controlled by the fractures. The stress has a clear impact on the fracture permeability, up to approximately four times the initial permeability. The water preferentially extracts the heat from the reservoir rock between fractures. When the intersecting angles of fractures are 10° and 30°, there exists a sufficient heat exchange domain and a shorter average distance between fractures, which can enhance the production efficiency. The well layout perpendicular to the shear deformation direction is conducive to delaying the lifespan of the EGS and extracting more heat over a longer exploitation time. These key results can provide reasonable suggestions for the optimal development strategy in EGSs.
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Data Availability Statement
No data, models, or codes were generated or used during the study.
Acknowledgments
The authors acknowledge the financial support of the National Natural Science Foundation of China (Grant No. 52074332) and Shandong Provincial Science Fund for Excellent Young Scholars (ZR2020YQ36).
Notations
The following symbols are used in this paper:
- C
- cumulative thermal production, J;
- Cfr
- fracture heat capacity, J/(kg · K);
- Cm
- rock heat capacity, J/(kg · K);
- Cw
- water heat capacity, J/(kg · K);
- dfr
- fracture aperture, m;
- Fi
- volume force, N/m3;
- G
- shear modulus, Pa;
- K
- volume modulus, Pa;
- kfr
- fracture permeability, m2;
- km
- rock permeability, m2;
- kn
- normal stiffness, Pa/m;
- p
- fluid pressure, Pa;
- Pout
- production thermal power, W;
- Qf
- flow exchange, kg/(m3 · s);
- Qf
- source/sink term, kg/(m3 · s);
- S
- storage coefficient, 1/Pa;
- Sfr
- storage coefficient, 1/Pa;
- T
- temperature, K;
- Tout
- production temperature,°C;
- u
- displacement, m;
- ufr
- fracture flow velocity, m/s;
- un
- normal displacement, m;
- uw
- flow velocity, m/s;
- Wf
- heat exchange, W/m3;
- αB
- Biot coefficient;
- αT
- thermal expansion coefficient;
- ɛV
- volume strain;
- η
- heat extraction ratio;
- λ
- lame constant;
- λfr
- fracture thermal conductivity, W/(m · K);
- λm
- rock thermal conductivity, W/(m · K);
- λw
- water thermal conductivity, W/(m · K);
- μw
- fluid viscosity, mPa·s;
- ρfr
- fracture density, kg/m3;
- ρm
- reservoir rock density, kg/m3;
- ρw
- water density, kg/m3;
- σn
- normal stress, Pa;
- normal effective stress, Pa;
- φfr
- fracture porosity; and
- φr
- reservoir rock porosity.
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Published In
International Journal of Geomechanics
Volume 24 • Issue 1 • January 2024
Copyright
© 2023 American Society of Civil Engineers.
History
Received: Mar 6, 2023
Accepted: Jul 10, 2023
Published online: Oct 31, 2023
Published in print: Jan 1, 2024
Discussion open until: Mar 31, 2024
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