Elastic laboratory measurements and modeling of saturated basalts
Elastic laboratory measurements and modeling of saturated basalts
复制标题
DOI：
10.1002/jgrb.50090
复制
发表时间：
2013-03
期刊：
影响因子：
--
通讯作者：
L. Adam;Thomas L. Otheim
中科院分区：
文献类型：
--
作者：
L. Adam;Thomas L. Otheim
了解玄武岩的弹性行为对于地震监测火山、海底玄武岩和玄武岩中的碳封存具有重要意义。我们估计了来自爱达荷州蛇河平原的玄武岩样品在超声波（0.8 MHz）和地震（2-300 Hz）频率下的弹性特性。为了测试地震波对孔隙结构中流体含量的敏感性，在三种饱和条件下进行了测量：饱和的液态二氧化碳、水和干燥。当二氧化碳取代水时，P波速度平均下降10%。在岩石微观结构中观察到的囊泡和裂缝控制着波传播过程中岩石孔隙流体压力的松弛。饱和液态CO2的玄武岩体积模量和剪切模量与频率无关，表明流体孔隙压力在2 Hz ~ 0.8 MHz之间处于平衡状态。然而，当样品是水饱和时，岩石的体积模量是频率相关的。用Gassmann方程建模可以预测频率低于20 Hz的所有流体的饱和岩石体积模量，但对频率高于20 Hz的水饱和玄武岩体积模量的预测不足。最可能的原因是孔隙流体压力不松弛。相反，超声频率岩石模量是用喷射流动和Kuster-Toksöz （KT）的高频弹性理论建模的。虽然KT的模型是基于理想的孔隙形状，但根据岩石学数据对球体（囊泡）和美分形裂缝（裂缝）的组合进行解释和量化，可以预测所测玄武岩的超声干燥和饱和岩石模量。
Understanding the elastic behavior of basalt is important to seismically monitor volcanoes, subsea basalts, and carbon sequestration in basalt. We estimate the elastic properties of basalt samples from the Snake River Plain, Idaho, at ultrasonic (0.8 MHz) and seismic (2–300 Hz) frequencies. To test the sensitivity of seismic waves to the fluid content in the pore structure, measurements are performed at three saturation conditions: saturated with liquid CO2, water, and dry. When CO2 replaces water, the P‐wave velocity drops, on average, by 10%. Vesicles and cracks, observed in the rock microstructure, control the relaxation of pore‐fluid pressures in the rock as a wave propagates. The bulk and shear moduli of basalts saturated with liquid CO2 are not frequency dependent, suggesting that fluid pore pressures are in equilibrium between 2 Hz and 0.8 MHz. However, when samples are water saturated, the bulk modulus of the rock is frequency dependent. Modeling with Gassmann's equations predicts the measured saturated rock bulk modulus for all fluids for frequencies below 20 Hz but underpredicts the water‐saturated basalt bulk modulus for frequencies greater than 20 Hz. The most likely reason is that the pore‐fluid pressures are unrelaxed. Instead, the ultrasonic frequency rock moduli are modeled with high‐frequency elastic theories of squirt flow and Kuster–Toksöz (KT). Although KT's model is based on idealized pore shapes, a combination of spheres (vesicles) and penny‐shaped cracks (fractures) interpreted and quantified from petrographical data predicts the ultrasonic dry and saturated rock moduli for the measured basalts.