不同冷却方式下高温花岗岩巴西劈裂及声发射特性试验研究

Experimental study on Brazilian split test and acoustic emission characteristics of high temperature granite under different cooling methods

干热岩地热开发中的钻井、储层压裂及热交换等环节均涉及高温岩石冷却的问题,为揭示其中岩石损伤演化规律,基于巴西劈裂试验和声发射技术,研究了不同高温及冷却方式对花岗岩抗拉性质的影响。结果表明:①25~600℃下花岗岩抗拉强度随温度升高而下降,遇水冷却使抗拉强度进一步下降并使其开始大幅下降的温度阈值提前到200,500℃后抗拉强度对遇水冷却更敏感。②荷载达到峰值,声发射累计振铃计数突增,岩样内形成断裂区;受遇水冷却影响,岩样的振铃计数峰值和能量峰值有所下降,间接反映岩石内裂纹更发育,200~300℃时降幅均较大,300℃时和500℃后花岗岩对热处理方式较敏感。③花岗岩破裂面随温度升高由平整向粗糙曲折变化,由脆性向延性转变,遇水冷却促进岩石破裂并促使脆性向延性转变的温度区间提前。研究结果为地热开采中高温岩石的稳定性评价提供理论参考。

High-temperature rock cooling can occur in the whole process of the drilling,fracturing,and heat exchange during the geothermal energy exploitation in hot dry rock.To reveal the evolution law of rock damage,based on the Brazilian splitting test and acoustic emission technology,the effects of different high temperatures and cooling methods on the tensile properties of granite were studied.The results showed that:①The tensile strength of granite decreases with increasing temperature from 25℃ to 600℃,and the temperature threshold,at which it decreases greatly,is advanced to 200℃after cooling with water.After 500℃,the tensile strength is more sensitive to water cooling.②When the load reaches the peak value,the cumulative ringing count of acoustic emission suddenly increases,and the fracture zone forms in the rock sample.Under the influence of water cooling,the ringing count peak value and energy peak value of the rock sample decrease,which indirectly reflects that the internal cracks of the rock are more developed,and both of their decrease range is larger at 200~300℃.The granite is more sensitive to heat treatment at 300℃ and after 500℃.③With the increase in temperature,the fracture surface of granite changes from flat to rough and tortuous,from brittle to ductile;Cooling in water promotes rock fracture and advances the temperature range from brittleness to ductility.The research results provide a theoretical reference for the stability evaluation of high-temperature rocks in geothermal exploitation.