考虑壁面接触率的花岗岩裂隙渗流传热特性试验研究

Experimental study on seepage heat transfer characteristics of granite fractures considering wall contact rate

为实现深部高温矿井围岩地热资源的高效化利用与精准化产能评估,开展接触型花岗岩裂隙的渗流-传热试验研究。测量天然裂隙在不同法向应力作用下的接触率,制备具有接触凸起的岩芯裂隙试件,研究接触裂隙的渗透性质和对流传热性质在不同温压条件下的演变规律,并通过引入有效换热面积改进传统对流换热系数评估模型。试验结果表明,接触裂隙的等效水力开度随围压的衰减程度受接触率控制,反映了非均质裂隙渗透性质对围压的不均匀响应过程。接触裂隙的闭合变形对围压响应程度不同,导致等效渗透率随接触率的增加在高围压状态下表现出先增加后的下降趋势,而在低围压状态下表现为单调减小趋势。同一水压力梯度下,高温裂隙的累计产热量随着接触率的增加首先增加,然后降低。改进的对流换热系数模型表明裂隙的对流换热系数与接触率表现出正相关关系,而传统理论模型无法刻画这一演变特征。忽略天然接触特征将导致高温裂隙的对流换热系数被低估,且低估程度随着接触率的增加而增加。此外,基于改进模型获取的对流换热系数与体积流量之间并不严格遵循幂律相关关系,依赖流量对裂隙换热系数的估计效果需要进一步提升。

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.