高温高压静水压条件下岩石纵波、横波速度和泊松比的实验研究

Experimental study on P-and S-wave velocities and Poisson’s ratios of rocks under high temperature and high hydrostatic pressure

为了研究高温高压静水压条件下的岩石的弹性物理参数,利用自行研发的高温高压静水压(气压)装置,结合超声脉冲反射法对4块典型灰岩样品进行了高温(25~400℃)高压静水压(0~300MPa)的纵波、横波的速度测量,并对所测岩石的泊松比进行了计算。实验结果表明,在常温高压下,当气体围压小于200MPa时,岩石的纵波和横波速度呈非线性快速增加,当围压大于200MPa时,波速近似呈线性缓慢增加;当气体围压小于200MPa时,岩石的泊松比增加较快,围压大于200MPa时,泊松比变化很小,由此可推测所测实验灰岩样品的孔隙闭合压力大约为200MPa。恒压高温下,当温度小于300℃时,围压限制了裂隙的热扩张,纵波和横波近似呈线性缓慢变化,泊松比表现为不变或者缓慢增加。当温度大于300℃时,300MPa的围压已不能限制温度导致的裂隙扩张,岩石纵波和横波速度降低,泊松比略微降低。

In order to study the elastic physical parameters of the rocks under high temperature and high hydrostatic pressure, in this paper, we used the self-designed experimental facility(high temperature and high hydrostatic pressure of gas) to have measured P-and S-wave velocities of four limestone samples under temperatures(25-400℃) and hydrostatic pressures(0-300 MPa) by means of ultrasonic pulse reflection method, and calculated the Poisson’s ratios of the rocks.The experimental results indicate that under room temperature and high pressure, with the increase of pressure, the P-and S-wave velocities of rocks are non-linearly and rapidly increased when the gas confining pressure is less than 200 MPa,but then they are approximated linearly increased when the gas confining pressure is higher than 200 MPa. In particular,the Poisson’s ratios of rocks are rapidly increased when the gas confining pressure is less than 200 MPa, however, they are limitedly changed when the confining pressure is greater than 200 MPa. Therefore, it can be inferred that the pore closing pressure of the limestone samples in this experiment is about 200 MPa. Under constant pressure and high temperature which is less than 300 ℃, the confining pressure had limited the thermal expansion of the fracture, the P-and S-wave velocities of rocks are changed linearly and slowly, and the Poisson’s ratios of rocks are generally constant or slightly increased. Under constant pressure and high temperature which is greater than 300 ℃, the confining pressure of 300 MPa can no longer limit the crack expansion caused by temperature, the P-and S-wave velocities of rocks are decreased, and the Poisson’s ratios are slightly decreased.