Deep geothermal energy is a renewable energy source with broad distribution,vast resource potential,and promising development prospects.Current main extraction methods include enhanced geothermal systems(EGS),annular heat exchange well systems(AGS),fault zone fluid circulation extraction,and coaxial casing ex-traction methods.However,challenges such as unstable heat extraction power,high seismic risks,and low heat ex-traction efficiency persist.Addressing the bottlenecks in current deep geothermal extraction technology,this paper adheres to the principle of energy exchange without material exchange during the extraction process and aims for large-scale,sustainable,and stable development of deep dry hot rock geothermal resources.We propose the clus-tered multi-branch U-shaped well heat extraction method(UMW-DGS)and its key technologies.On this basis,an axisymmetric thermal conduction model for the wellbore is established.Using the deep dry hot rock reservoir in the Qabqa area of the Gonghe Basin in Qinghai as a case study,a new method for testing the thermal conductivity of high-temperature and high-pressure rocks is proposed.We calculated the spatiotemporal evolution of the temperature field and heat extraction power around the well under constant wellbore diameter conditions and analyzed the effects of three sensitive factors—temperature difference,thermal conductivity,and wellbore diameter—on heat extraction power.Additionally,to address the boundary value problem of the UMW-DGS,a three-dimensional thermo-hydro-mechanical coupling numerical algorithm based on the finite volume method(FVM)was developed.This algorithm was used to study the heat exchange efficiency of a single horizontal well section of the UMW-DGS and the spatio-temporal evolution of the temperature field under different injection flow conditions.By analyzing the effective heat exchange amount,duration,and power at different flow rates,we found that increasing the injection flow rate de-creases the effective heat exchange energy and duration while causing the effective heat exchange power to first in-crease and then decrease.The research results indicate that deep geothermal energy development requires designing injection flow rates to balance heat exchange temperature and power for optimal heat exchange efficiency.
关键词
深层地热/丛式多分支U型井/高温高压岩石热导率/储层-工质流固耦合热传导算法
Key words
Deep geothermal energy/Clustered multi-branch U-shaped wells/Thermal conductivity of high-tem-perature and high-pressure rocks/Reservoir-working fluid thermo-hydro-mechanical coupled heat conduction algo-rithm
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