An Investigation of the Thermoelastic Effect in Enhanced Geothermal System Reservoirs Using a Fully-Coupled Thermo-Hydro-Mechanical Model

2021 ◽  
Author(s):  
Musa D. Aliyu ◽  
Rosalind A. Archer ◽  
Huapeng Chen
Keyword(s):  
Mechanical Model ◽  
Geothermal System ◽  
Enhanced Geothermal System ◽  
Thermoelastic Effect ◽  
Fully Coupled

Impact of convective cooling on pore pressure and stresses around a borehole subjected to a constant flux: Implications for hydraulic tests in an enhanced geothermal system reservoir

2020 ◽  
Vol 8 (2) ◽  
pp. SG13-SG20 ◽  
Author(s):  
Zhiqiang Fan ◽  
Rishi Parashar ◽  
Zhi-He Jin
Keyword(s):  
Pore Pressure ◽  
Analytical Solutions ◽  
Cold Water ◽  
Borehole Wall ◽  
Geothermal System ◽  
Enhanced Geothermal System ◽  
Inversion Algorithm ◽  
Thermoelastic Effect ◽  
Hydraulic Test ◽  
Convective Cooling

Hydraulic tests are commonly performed prior to reservoir stimulation to determine the natural permeability of the enhanced geothermal system (EGS), which typically involves injection of cold water at low rates into the hot target EGS reservoir and measurement of the surface pressure, flow rate, and thermal drawdown simultaneously. Interpretation and analysis of the data collected during a hydraulic test are largely based on fitting type curves generated from analytical solutions. We have formulated a geomechanical model for hydraulic tests in a thermoporoelastic EGS reservoir in which the open-hole section of the borehole wall is subjected to a constant-rate flux and convective cooling. We derive the analytical solutions for injection induced axisymmetric deformation, temperature drawdown, pore pressure, and stresses in the Laplace domain, and we obtain time-domain solutions using the Stehfest inversion algorithm. We evaluate numerical examples to illustrate the competition between the thermoelastic effect and the poroelastic effect in controlling temperature, pore pressure, and stresses around the borehole wall. The numerical results indicate that temperature drawdown at the borehole wall would be significantly overestimated if a constant temperature boundary condition instead of convective cooling is used. At early times, injection induced hoop stress/pore pressure is partially offset by the corresponding ones induced by convective cooling. At late times, convective cooling plays a marginal role in influencing pore pressure and stress around the borehole. The analytical solutions are helpful to address the thermohydromechanical coupling mechanisms controlling pressure perturbations during hydraulic tests conducted in an EGS reservoir.

scholarly journals Performance of Hybrid Single Well Enhanced Geothermal System and Solar Energy for Buildings Heating

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2473
Author(s):  
Yujiang He ◽  
Xianbiao Bu
Keyword(s):  
Solar Energy ◽  
Service Life ◽  
Heating System ◽  
Hydrothermal Systems ◽  
Geothermal System ◽  
Heat Output ◽  
Enhanced Geothermal System ◽  
Geothermal Heat ◽  
Hybrid Heating ◽  
Single Well

The energy reserves in hot dry rock and hydrothermal systems are abundant in China, however, the developed resources are far below the potential estimates due to immature technology of enhanced geothermal system (EGS) and scattered resources of hydrothermal systems. To circumvent these problems and reduce the thermal resistance of rocks, here a shallow depth enhanced geothermal system (SDEGS) is proposed, which can be implemented by fracturing the hydrothermal system. We find that, the service life for SDEGS is 14 years with heat output of 4521.1 kW. To extend service life, the hybrid SDEGS and solar energy heating system is proposed with 10,000 m2 solar collectors installed to store heat into geothermal reservoir. The service life of the hybrid heating system is 35 years with geothermal heat output of 4653.78 kW. The novelty of the present work is that the hybrid heating system can solve the unstable and discontinuous problems of solar energy without building additional back-up sources or seasonal storage equipment, and the geothermal thermal output can be adjusted easily to meet the demand of building thermal loads varying with outside temperature.

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