干热岩体热冲击后纵波波速演化规律研究

Study on law of longitudinal wave velocity evolution of dry hot rock after thermal shock

干热岩体花岗岩受构造运动影响,产生规模较大的节理裂隙,形成裂隙干热岩体,这些裂隙在后期被热液充填后,称后期热液充填裂隙干热岩体,充填体与母岩的胶结面是一个弱面,利用该弱面极易于建造干热岩地热人工储留层,大幅节省建造成本。为研究实际干热岩地热开发中注入低温水热冲击后母岩、充填体及其胶结面性质的演化规律,利用超声波检测技术研究了4类ø50 mm×100 mm标准岩样(花岗岩母岩、充填体、含纵向胶结面充填花岗岩、含横向胶结面充填花岗岩)在室温至600℃高温条件下反复热冲击及不同冲击氛围(0℃水冷却冲击和室温冷却冲击)下的纵波波速演化规律。研究结果表明:室温下含胶结面充填花岗岩的开口孔隙率较母岩、充填体低,而波速较母岩、充填体大;室温-300~0℃水反复热冲击过程中,4类岩样在首次热冲击后波速降幅可达40%~50%,之后随着热冲击次数增加波速降幅减小,约3%;相同高温下,4类岩样在0℃水冷却冲击后的波速降幅均较室温冷却冲击时大,说明0℃水冷却冲击对岩石的损伤更强;相同热冲击方式下,含胶结面充填花岗岩波速降幅较母岩、充填体大,这是因为胶结面附近的矿物颗粒尺度差异最大,热破裂程度最强。研究结果对断层模式干热岩地热开发中储留层的建造及开发过程中储留层结构演化的认识有重要指导意义。

Due to the influence of tectonic movement,the dry hot rock mass granite produces large-scale joint fissures,forming a fractured dry hot rock mass,these fissures are later filled with hydrothermal fluid to form a late hydrothermal filling fractured dry hot rock mass.The cementation surface between the filling body and the parent rock is a weak surface,which is very easy to build geothermal artificial reser⁃voir of dry hot rock and greatly saves the construction cost.In order to study the evolution law of parent rock,filling body and cementation surface after injecting low temperature hydrothermal shock in the geothermal development of actual dry hot rock,four kinds of standard samples(granite parent rock,filling body,filling granite with longitudinal cementation surface and filling granite with transverse cementa⁃tion surface)were studied by ultrasonic testing technology under the condition of repeated thermal shock from room temperature to 600℃and different shock atmosphere(water cooling shock at 0℃and cooling shock at room temperature).The results show that:at room tem⁃perature,the porosity of granite with cemented surface is lower than that of parent rock and filling body,while the wave velocity is higher than that of parent rock and filling body.During the repeated thermal shock of room temperature-300~0℃water,the wave velocity of the four types of samples can be reduced by 40%-50%after the first thermal shock,and then the wave velocity decreases by about 3% with the increase of the number of thermal shocks.At the same high temperature,the wave velocity drop of four kinds of samples after water cooling shock at 0℃is larger than that at room temperature,which indicates that water cooling shock at 0℃has stronger damage to rock.Under the same thermal shock mode,the wave velocity drop of the filling granite with cemented surface is larger than that of the parent rock and the filling body,because the size difference of the mineral particles near the cemented surface is the largest,and the degree of thermal cracking is the strongest.The research results are of great significance to the understanding of the formation and structural evolution of the reservoirs in the fault model dry hot rock geothermal field.