高温及动态剪切下花岗岩裂隙渗流与传热特性试验研究

Experimental study on seepage and heat transfer characteristics evolution of fractured granite induced by dynamic shear slip at high temperature

深部地热储层赋存有大量闭合裂隙,通过注水诱发裂隙剪切滑移,可实现储层渗透及换热性能的改造。开展不同温度(25℃~300℃)条件下花岗岩裂隙动态剪切–渗流–传热试验,分析花岗岩裂隙动态剪切滑移过程中实时渗透率与对流换热系数演化,定量表征裂隙面形貌及微凸体剪切损伤,揭示高温作用下花岗岩裂隙剪切损伤对渗流及传热特性影响机制。结果表明:(1)花岗岩裂隙渗透率与对流换热系数随剪切滑移呈平稳–增长–衰减三阶段变化特征,这与裂隙面微凸体剪缩、剪胀、剪断及碎屑物堵塞等有关;(2)随着花岗岩温度由25℃增至300℃,初始平稳段渗透率变化不大,而剪切滑移过程中增长段与衰减段的渗透率增幅K_(2)/K_(0)和K_(3)/K_(0)均减小,其中K_(2)/K_(0)由159.75降至30.58,而K_(3)/K_(0)由148.68降至3.03;(3)花岗岩裂隙剪切过程中,对流换热系数变化与渗透性呈正相关关系,且花岗岩温度越高,对流换热系数越大;(4)花岗岩温度越高,裂隙面微凸体剪切破坏越严重,当温度由25℃增至300℃,损伤体积由508.1 mm^(3)增至729.3 mm^(3),裂隙面剪切磨损物粒径越小,磨损物堵塞对裂隙渗透率及对流换热系数的衰减作用更加明显。研究结果对高温岩体地热开采过程中高温岩体裂隙运动变形及热能高效开采具有一定理论指导意义与价值。

In deep geothermal reservoirs,a multitude of sealed rock fractures are prevalent.Utilizing hydraulic stimulation to induce shear along these fractures can significantly enhance the permeability and convective heat transfer performance of geothermal reservoirs.To investigate this mechanism,a series of shear tests were conducted on granite fractures at different temperatures(25℃to 300℃),and the evolution of permeability and convective heat transfer coefficient during the shear were measured concurrently.Through quantitatively characterizing the changes in surface morphology and the damage to surface asperities caused by shear slip,the mechanism of high temperature and shear induced damage effects on the permeability and heat transfer characteristics of fractured granite was revealed.The results show that:(1)the permeability and convective heat transfer coefficient of granite during shear slip exhibit three stages,which are closely related to shear-induced changes such as shrinkage,dilatancy,asperity damage,and gouge production;(2)The permeability K_(1)in the stable stage exhibits minimal correlation with temperature.However,as the temperature increases from 25℃to 300℃,the rate of permeability increase K_(2)/K_(0)during the growth stage gradually decreases from 159.75 to 30.58,and during the attenuation stage,it decreases from 148.68 to 3.03.(3)There is a positive correlation between the convective heat transfer coefficient and permeability.Higher temperatures in granite are associated with higher convective heat transfer coefficients.(4)Higer temperatures exacerbate shear damage to surface asperities.As the temperature increases from 25℃to 300℃,the damage volume increases from 508.1 mm^(3)to 729.3 mm^(3).The production of smaller particles from shearing contributes to the enhanced attenuation effect of gouge blockage on permeability and convective heat transfer coefficients during shear slip.This research provides valuable insights for the efficient extraction of heat energy from dry hot rocks.