We show that direct estimates of the permeability of hydrate-bearing geological formations are possible from remote measurements of shear wave velocity (V_s) and attenuation (Q_s⁻¹). We measured V_s, Q_s⁻¹ and electrical resistivity at time intervals during methane hydrate formation in Berea sandstone using a laboratory ultrasonic pulse-echo system. We observed that V_s and Q_s⁻¹ both increase with hydrate saturation S_h, with two peaks in Q_s⁻¹ at hydrate saturations of around 6% and 20% that correspond to changes in gradient of V_s. We implemented changes in permeability with hydrate saturation into well-known Biot-type poro-elastic models for two- and three-phases for low (S_h < 12%) and high (S_h > 12%) hydrate saturations respectively. By accounting for changes in permeability linked to hydrate morphology, the models were able to describe the V_s and Q_s⁻¹ observations. We found that the first Q_s⁻¹ peak is caused by a reduction of permeability during hydrate formation associated with a transition from pore-floating to pore-bridging hydrate morphology; similarly, the second Q_s⁻¹ peak is caused by a permeability reduction associated with a transition from pore-bridging hydrate morphology to an interlocking network of hydrate in the pores. We inverted for permeability using our poro-elastic models from V_s and Q_s⁻¹. This inverted permeability agrees with permeability obtained independently from electrical resistivity. We demonstrate a good match of our models to shear wave data at 200 Hz and 2 kHz frequencies from the literature, indicating the general applicability of the models.

中文翻译：

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天然气水合物形态对储层渗透率和地球物理剪切波遥感的影响

我们表明，通过远程测量剪切波速度 ( V _s ) 和衰减 ( Q _s ^-1 )可以直接估计含水合物地质地层的渗透率。我们使用实验室超声波脉冲回波系统测量了 Berea 砂岩中甲烷水合物形成期间的时间间隔V _s、Q _s ^-1和电阻率。我们观察到V _s和Q _s ^-1都随着水合物饱和度S _{h 的}增加而增加，在Q _s ^{-1 中}有两个峰值在 6% 和 20% 左右的水合物饱和度对应于V _s梯度的变化。我们实施改变渗透性水合物饱和成公知的毕奥-型波罗弹性模型两个和三个阶段为低（小号_ħ  <12％）和高（小号_ħ 分别水合物饱和度> 12％）。通过考虑与水合物形态相关的渗透率变化，这些模型能够描述V _s和Q _s ^-1观测值。我们发现第一个Q _s ^-1峰值是由水合物形成过程中渗透率的降低引起的，与从浮孔到孔桥水合物形态的转变有关；类似地，第二个Q _s ^-1峰是由渗透率降低引起的，渗透率降低与从孔桥水合物形态转变为孔内水合物互锁网络相关。我们使用来自V _s和Q _s ^{-1 的}多孔弹性模型对渗透率进行了反演。这种反向渗透率与独立于电阻率获得的渗透率一致。我们展示了我们的模型与文献中 200 Hz 和 2 kHz 频率的剪切波数据的良好匹配，表明模型的普遍适用性。