多级围压下砂岩单裂隙渗流传热试验研究

Experimental Study on Seepage and Heat Transfer of Sandstone with Single Fracture Under Multi-Level Confining Pressure

为研究不同围压下砂岩平直单裂隙的渗流传热特性,采用自主研制的高温三轴渗流-换热试验系统,以蒸馏水为换热介质,进行不同围压和不同温度下的对流换热试验。试验设置4,4.5,5,5.5,6MPa 5个围压水平,对低温区(T=50℃、70℃、100℃)的对流换热规律进行了分析,还创新性地开展了高温区(T=130℃)的对流传热试验。结果表明:(1)在相同温度、围压下,提高流速,渗透压力增大,导致裂隙开度随流速的增加而变大;在相同流速、围压下,温度升高使岩样骨架膨胀,弹性模量变小,岩样裂隙闭合程度加大,裂隙开度随温度的升高而变小;在相同温度、流速下,加大围压,裂缝紧密贴合,渗流通道进一步减小,开度也随之减小;(2)换热系数与流速、温度呈正相关,与开度呈负相关,高温下换热系数相对于低温时对流速、开度的变化更加敏感,高流速下换热系数相对于低流速时对温度、开度的变化更加敏感;(3)通过对比流速、温度、开度3个因素对换热系数的影响,发现流速、温度对换热系数的影响比开度的影响强。研究结果对断层模式地热开发中提高干热岩换热效率有重要指导意义。

In order to study the seepage and heat transfer characteristics of sandstone with flat single fracture under different confining pressures,a self-developed experiment system of seepage and heat transfer in high temperature was used to carry out the convection heat transfer tests under different confining pressures and temperatures with distilled water as the thermal quality.In the tests,five confining pressure levels(4,4.5,5,5.5,6 MPa)were set up to analyze the convection heat transfer law at the low temperature zone(T=50℃,70℃,100℃).In addition,the convection heat transfer tests at the high temperature zone(T=130℃)were carried out innovatively.The results are concluded as follows.(1)With the same temperature and confining pressure,increasing velocity and seepage pressure will lead to the increase of fracture opening with the increase of velocity.Under the same flow rate and confining pressure,the increase of temperature would expand the skeleton of rock sample,decrease the elasticity modulus,increase the degree of fracture closure,and decrease the degree of fracture openings with the increase of temperature.At the same temperature and flow rate,with the increase of the confining pressure,the cracks fit closely,the seepage channel further decreases,and the opening also decreases.(2)The heat transfer coefficient is positively correlated with the flow rate and temperature,and negatively correlated with the opening;the heat transfer coefficient at high temperature is more sensitive to the change of flow rate and opening compared with that at low temperature,and the heat transfer coefficient at high flow rate is more sensitive to the change of temperature and opening compared with that at low flow rate.(3)It is found that the influences of flow rate,temperature and opening on heat transfer coefficient are stronger than that of opening.The research results have an important guiding significance for improving the heat transfer efficiency of dry heat rock in fault model geothermal development.