Experimental study on seepage heat transfer characteristics of granite fractures considering wall contact rate
Seepage and heat transfer experiments of contact-type granite fractures were conducted to realize the efficient utilization and accurate productivity evaluation of geothermal resources in the surrounding rock of deep high-temperature mines.The contact rate of natural fractures under different normal stresses was measured,and the core fracture specimens with contact asperities were prepared.The evolution of permeability and convection heat transfer properties of contact fractures under different temperature-pressure conditions were studied,and the traditional evaluation model of the convective heat transfer coefficient was improved by introducing an effective heat transfer area.Results show that the attenuation degree of the equivalent hydraulic aperture of the contact fracture with the confining pressure is controlled by the contact rate,which reflects the uneven response process of the permeability of heterogeneous fracture to the confining pressure.The closure deformation of contact fractures has different degrees of response to confining pressure,resulting in an increase followed by a decrease in equivalent permeability with increasing contact rate under high confining pressure,while it shows a monotonic decrease under low confining pressure.Under the same pressure gradient,the cumulative heat production of high-temperature fractures first increases and then decreases with the increase in contact rate.The improved convective heat transfer coefficient model indicates a positive correlation between the convective heat transfer coefficient and the contact rate,which cannot be characterized by traditional theoretical models.Neglecting the natural contact characteristics will lead to the underestimated convection heat transfer coefficient of high-temperature fractures,and the underestimated degree will increase with the increase in contact rate.In addition,the convection heat transfer coefficient obtained based on the improved model does not strictly follow the power law correlation relationship with the volume flow rate,and the estimation effect of the fracture heat transfer coefficient depending on the flow rate needs to be further improved.
rock mechanicsfracturecontact rateheat transferseepage characteristicsconvective heat transfer coefficient
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