论文详情
为了研究孔隙度、孔隙结构、含水饱和度、压力、频率等对致密砂岩纵、横波速度的影响，利用脉冲透射法、差分共振声谱法和低频应力应变方法得到了6块致密砂岩样品的纵、横波速度，并利用Micro-CT得到了岩石的微观孔隙结构。实验结果表明，岩石样品的孔隙度与密度具有较好的负相关性；超声频率下，干燥岩样的纵、横波速度和孔隙度相关性较差，而饱水岩样的纵、横波速度与孔隙度相关性变好；样品纵波速度随围压增加急剧增大，围压增加到20 MPa时，其纵波速度增大了23%，这主要受岩石裂缝闭合的影响；不同含水饱和度下，在1 558 Hz下测得的纵波速度比1 MHz的纵波速度低3.5%～12.5%；从干燥到完全水饱和，1 MHz和600 Hz频率下体积模量均增加，两者变化趋势大体相同，且与岩石的渗透率具有较好的相关性。
To study the influence of porosity,pore structure,confining pressure,water saturation and frequency on vP and vS in tight sandstone,we achieved the acoustic properties of six tight sandstones by using pulse transmission method,differential acoustic resonance spectroscopy method and low-frequency strain-stress method,and also obtained the microstructure of the samples by the Micro-CT.Results show that the porosity of tight sandstone samples has fine negative correlation with their density.The correlation between vP and vS and the porosities for dry samples is poor at ultrasonic frequency,but gets better for samples with 100% water saturation.The vP increases sharply with the increasing of confining pressure.When the confining pressure increases from 0.1 MPa to 20.0 MPa,the vP both at low and high frequencies increase by nearly 23% due to the closure of the fractures.Acoustic velocities at 1 558 Hz are roughly 3.5%~12.5% lower than ultrasonic velocities at 1 MHz at different water saturation.From dry to fully water saturation,the bulk modulus increases both at 1 MHz and 600 Hz,and has the same increasing trend,which shows a good correlation with the permeability of the samples.