高温高压下超临界二氧化碳作用对花岗岩力学性质影响的试验研究

为了研究二氧化碳基增强型地热系统核心及邻近区域中超临界二氧化碳(ScCO₂)作用对岩石力学性能的影响,设计了纯ScCO₂与干燥花岗岩作用,ScCO₂、水蒸气与干燥花岗岩作用,ScCO₂与在水中浸泡了24 h后的花岗岩作用3种试验条件,每种试验条件下均开展了210、240、270℃温度下的试验。对ScCO₂作用后的岩样以及一个未经处理的对比样先后开展纵波波速测试以及单轴压缩试验,获得了岩石的纵波波速、单轴抗压强度以及弹性模量。纵波波速试验结果表明,在上述3种试验条件下,花岗岩样的波速会都会发生一定程度的降低。单轴压缩试验结果表明,ScCO₂作用后的岩石单轴抗压强度及弹性模量都几乎没有受到影响,但是从破坏模式看,未经处理的岩石以张拉破坏为主,处理后的岩石以剪切破坏为主,并且随着温度的升高剪切破坏越明显。试验结果说明,在不存在水或者仅有微量水存在的情况下,ScCO₂的作用对岩石产生轻微损伤,岩样的刚性减弱、塑性增强,导致其纵波波速有少量的下...

Mechanical properties of granite after reaction with ScCO2 at high temperature and high pressure

In order to study the effect of supercritical carbon dioxide(ScCO₂) on the mechanical properties of granite located in the CO₂ based enhanced geothermal system(EGS) region, fluid-rock interaction experiments were conducted at 210 ℃, 240 ℃ and 270 ℃. Three experimental conditions were used: i) ScCO₂ and dry granite;ii) ScCO₂, water vapor and dry granite;iii) ScCO₂ and granite that is soaked in water for 24 hours. The P-wave velocities, uniaxial comprehensive strength, and elastic modulus of all these ScCO₂ treated granite samples and one untreated granite sample were obtained by carrying out the wave velocity tests and uniaxial compressive tests. Wave velocity tests show that the P-wave velocities of all these ScCO₂ treated granite samples are reduced compared to that of the untreated sample. Uniaxial compressive test show that the uniaxial comprehensive strength and elastic modulus are not affected. From the failure mode, it can be seen that the untreated granite more likely present brittle tensile failure,while the treated sample shows more likely shear failure. As the temperature increases, the failure mode becomes more and more close to shear failure. Experimental results show that the ScCO₂ has very slight damage impact on granite that has no water or little water, causing a slight decrease in the brittleness, and a small increase on the plasticity. The P-wave velocity decreases slightly and the damage to the granite strength can be negligible. Therefore, the interaction of CO₂-rock will not cause obvious effect on the mechanical properties of granite located in and nearby the CO₂-EGS region.