摘要
采用自主研制的"20MN伺服控制高温高压岩体三轴试验机",运用光学原理钻孔变形观测仪器,对φ200mm×400mm花岗岩体内含φ40mm的钻孔在6000m埋深静水应力及600℃以内恒温恒压下钻孔变形规律及其临界失稳条件进行深入细致的试验研究和理论分析。研究结果表明:(1)高温高压下花岗岩中钻孔变形随温度和应力的增大表现为明显的不同阶段。4000m埋深静水应力及400℃以内恒温恒压下,钻孔变形表现为明显的黏弹性变形阶段,钻孔直径虽有减小但仍处于稳定状态,并不发生破坏;4000~5000m埋深静水应力及400℃~500℃时恒温恒压下,钻孔变形表现为黏弹-塑性变形阶段,钻孔围岩有破坏的趋势,孔径开始增大;5000m埋深静水应力及500℃以上时,钻孔围岩塑性区的块裂状围岩颗粒逐渐从孔壁脱落下来,钻孔发生破坏。(2)花岗岩中钻孔围岩在超过应力阈值和温度阈值后,即5000m埋深静水应力及500℃以外时,钻孔破坏,发生塌孔现象,花岗岩颗粒从孔壁脱落下来,钻孔直径增大。(3)钻孔围岩在高温静水应力下,岩体最终发生破坏的应力条件为5000~6000m埋深静水应力(即125~150MPa)及500℃~600℃,其破坏形式为压裂破坏、压剪破坏或两者相结合。(4)高温高压下花岗岩中钻孔变形失稳临界条件为4000~5000m埋深静水应力,400℃~500℃。同时,根据试验研究结论,运用黏弹塑性力学理论给出高温高压下钻孔变形的分析理论,建立4000m埋深静水应力及400℃以内恒温恒压下钻孔变形的黏弹性理论模型及4000~5000m,埋深静水应力400℃~500℃时恒温恒压下钻孔变形的黏弹-塑性理论模型,为我国高温岩体地热(HDR)开发与利用中钻孔稳定性及维护问题、大陆科学钻探工程(CCSD)在深孔和超深孔施工过程中遇到的钻孔稳定性问题提供科学依据和理论指导。
Utilizing the 20 MN servo-controlled triaxial rock testing machine with high temperature and high pressure developed by the authors and using optical observation instrument of borehole deformation made by theory of optics,the intensive study of deformation laws and instability critical conditions of large-size granite with φ 40 mm borehole samples of φ 200 mm×400 mm within 600 ℃ and triaxial hydrostatic stress in depth of 6 000 m is carried out. The research results are as follows:(1) The deformation of borehole in granite bored with the increase of temperature and stress performance is obvious at different stages with high temperature and high pressure. Within hydrostatic stress of 4 000 m in depth and temperature at 400 ℃,drilling performance is obvious at the moment of viscoelastic stage. Although borehole diameter reduces but still in stable condition, and damage does not occur. The hydrostatic stress of 4 000–5 000 m in depth and the temperature at 400 ℃– 500 ℃,the deformation of borehole is at viscoelastic-plastic stage and the surrounding rock near drilling shows a destructive trend,and the aperture begins to increase. Under 5 000 m hydrostatic stress in depth and temperature more than 500 ℃ when the cracked rock-like particles block in plastic zone gradually fall down from the hole wall,the borehole is in damage. (2) When the surrounding rock of granite in more than creep threshold of stress and creep threshold of temperature,which is over hydrostatics stress of 5 000 m in depth and temperature than 500 ℃,the borehole is in destruction and the collapse of a borehole phenomenon occurs. At the same time, the particles of surrounding rock in granite are falling down;and the hole diameter is increasing. (3) At different temperatures and hydrostatic stresses in depths,the critical hydrostatic stress of rheodestruction of surrounding rock is 5 000–6 000 m (that is 125–150 MPa);and the critical temperature of rheodestruction is 500 ℃–600 ℃. The failure modes are of compression fracture,transpression or both of them. (4) The critical condition of borehole instability in granite under high temperature and stress is hydrostatic stress of 4 000–5 000 m in depth and temperature at 400 ℃–500 ℃ . These research can provide a scientific basis and theoretical guidance for hot dry rock(HDR) development to utilize the drilling in the maintenance of stability and Chinese continental scientific drilling(CCSD) in the aspect of ultra-deep hole and deep hole in the construction of drilling encountered in the process of stability.