Summary Understanding the influence of pore fluids on acoustic characteristics of rocks containing pores of low aspect ratio, i.e. cracks is crucial for both laboratory and field observations of seismic exploration. Unlike the petrophysical aspects of conventional rock species, those of tight dolomites are relatively more complex and poorly understood. To address this problem, we investigated the ultrasonic velocity of dry and saturated tight dolomite in the effective pressure range of 2–60 MPa and analyzed the variation in shear modulus upon fluid saturation. Our results showed that while undergoing the change in form from the dry state to being saturated with water, the rock may weaken or harden, and the shear modulus may correspondingly either decrease or increase. Shear modulus hardening was more apparent in dolomites, with microcracks mostly dispersed between and within particles of a high proportion of soft pores with a wide distribution range of aspect ratio. This study used the Walsh–Hudson model to satisfactorily simulate the hardening of shear modulus in fluid-saturated tight dolomites. The suppression of squirt flow that is responsible for the increased shear modulus of fluid-saturated tight dolomites tested at sufficiently high frequencies. As the change in shear modulus affects the prediction of longitudinal and shear wave velocities, using Gassmann's theory to fluid substitution in unconventional reservoirs such as tight dolomite may yield inaccurate results. Therefore, it may be necessary to consider variation in shear modulus while selecting the appropriate simulation model.

中文翻译：

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孔隙流体对致密白云岩剪切模量硬化的影响：实验观察和理论建模

小结 了解孔隙流体对包含低纵横比孔隙（即裂纹）的岩石声学特性的影响对于地震勘探的实验室和野外观测都是至关重要的。与常规岩石种类的岩石物理方面不同，致密白云岩的岩石物理方面相对更复杂且了解甚少。为了解决这个问题，我们在 2-60 MPa 的有效压力范围内研究了干燥和饱和的致密白云岩的超声波速度，并分析了流体饱和时剪切模量的变化。我们的结果表明，在经历从干燥状态到饱和水的形态变化时，岩石可能会变弱或变硬，并且剪切模量可能会相应地降低或增加。剪切模量硬化在白云岩中更为明显，微裂纹多散布于颗粒间和颗粒内，软孔比例高，纵横比分布范围广。本研究使用 Walsh-Hudson 模型令人满意地模拟了流体饱和致密白云岩中剪切模量的硬化。喷射流的抑制导致在足够高的频率下测试的流体饱和致密白云岩的剪切模量增加。由于剪切模量的变化会影响纵波和剪切波速度的预测，因此使用 Gassmann 理论对致密白云岩等非常规储层进行流体置换可能会产生不准确的结果。因此，在选择合适的模拟模型时可能需要考虑剪切模量的变化。