Asynchronous transport of heat and silica with fracture-aperture feedback in enhanced geothermal systems

In enhanced geothermal systems, the differences in propagation timescales between temperature and reactive-solute disturbances, together with their effects on fracture-aperture feedback, remain insufficiently quantified. This study employs a three-dimensional thermo-hydro-mechanical-chemical coupled model and uses the 50% normalized response time to quantitatively characterize the propagation differences between temperature and silica concentration disturbances, followed by an analysis of fracture-aperture evolution and its feedback on transport. The results show that, although the two disturbances propagate along the same preferential fracture pathways, they exhibit distinctly different propagation timescales. As the distance from the injection well increases from 50 to 300 m, the thermo-chemical response lag increases from 2.00 to 26.22 years. This time lag allows low-concentration fluid to continuously drive silica dissolution before the temperature reaches 50% response, with the chemical aperture at all locations reaching more than 98% of its value at 40 years. Fracture-aperture evolution also exhibits pronounced spatial variability: the reduction in mechanical closure is more evident near the injection well, whereas the chemical aperture increases with distance from the injection well. Under fully dynamic fracture-aperture conditions, silica concentration propagation is consistently delayed throughout the 50–300 m range, whereas the effect on temperature propagation changes from retardation near the injection well to enhancement farther downstream, with the feedback direction switching between 150 and 175 m. These results indicate that the separation of propagation timescales between temperature and silica concentration leads to earlier fracture-aperture evolution and subsequently affects heat and solute transport.