The development of deep geothermal energy is an important way to realize the goal of"double carbon".Due to the difference in diagenetic environments,the mineral composition and fine structure of deep granites are quite different from those of shallow granites.The coarse-grained granite of Luya Mountain,Shanxi Province,which represents a deep geothermal reservoir,was selected as research object.Using a three-axis seepage measurement system,the evolution laws of permeability and pore structure were systematically studied under rapid cooling with pulse pressure impact method and mercury intrusion method.It is found that the threshold temperature for permeability of coarse-grained granite is 250 ℃ under unconfined and slowly heating conditions.Multiple"heating-cooling"cycles can increase permeability and porosity,but the increase decreases as the number of cycles increases.Increasing the heat treatment temperature and the number of"heating-cooling"cycles are conducive to the formation of oversized holes and large holes.When the heat treatment temperature reaches 400 ℃,the microporous start to generate.Both the physical properties and temperature sensitivity of the coarse-grained granite are favorable for the development of deep geothermal reservoirs.
Deep geothermal developmentCoarse-grained granitePermeabilityPore structureSharp cooling
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