The Mancos shale core sample investigated in the present research has been extracted from the late Cretaceous (upper cretaceous) geologic formation of USA. Shale gas is usually obtained by horizontal drilling which induces fractures to increase the flow ability of hydrocarbons. Therefore, it is important to understand the mechanical properties, heterogeneity, and their complexities associated with elastic properties of shale. An experimental study was conducted to examine the morphological characteristics of the Mancos shale core sample both pre- and post-treatment with cryogenic liquid nitrogen (LN₂) for various immersion times, namely, 30, 60, and 90 min. The atomic force microscopy technique is used to understand the surface roughness, irregularities in core samples, and for more accuracy. Scanning electron microscopy (SEM) results were employed to visualize the formation of cracks caused by cryogenic liquid nitrogen. Results from SEM showed an increase in the fracture size from 2 to 25 μm with an increase in the aging time up to 90 min under the atmosphere of cryogenic LN₂. Nano-indentation measurements revealed that the nano-indentation moduli of the Mancos samples subjected to applied forces of 50 and 200 mN underwent a decrease from 24.6 to 16.8 and 15.6 GPa, respectively, with an increase in cryogenic liquid nitrogen treatment time to 90 min. The permeability of the shale samples after LN₂ treatment showed a significant increase, whereas increasing net confining stress from 1000 to 7000 psi for all untreated and treated rock samples exhibited a decrease in permeability, which is attributed to increased compaction between the pore spaces. Moreover, the porosity of the Mancos shale increased from 3.78 to 6.92% for pretreated and treated rock samples.

中文翻译：

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低温液氮对Mancos页岩岩石物理特性的影响：实验研究

本研究中研究的Mancos页岩岩心样品是从美国晚白垩世（上白垩统）地质构造中提取的。页岩气通常通过水平钻井获得，这会引起裂缝，从而增加碳氢化合物的流动能力。因此，重要的是要了解机械性能，非均质性及其与页岩弹性特性相关的复杂性。进行实验研究以检查Mancos页岩岩心样品的低温液氮（LN _2）预处理和后处理的形态特征）的浸泡时间，即30、60和90分钟。原子力显微镜技术用于了解表面粗糙度，岩心样品中的不规则性并提高准确性。扫描电子显微镜（SEM）结果用于可视化低温液氮引起的裂纹的形成。SEM结果表明，在低温LN ₂气氛下，断裂尺寸从2μm增加到25μm，并且随着时效时间的延长，长达90分钟。纳米压痕测量表明，受到50和200 mN施加力的Mancos样品的纳米压痕模量分别从24.6降低到16.8和15.6 GPa，而低温液氮处理时间增加到90分钟。LN后页岩样品的渗透率₂处理显示出显着增加，而所有未处理和处理过的岩石样品的净围压从1000 psi增加到7000 psi，渗透率降低，这归因于孔隙空间之间的压实度增加。此外，对于经过预处理和处理过的岩石样品，Mancos页岩的孔隙度从3.78％增加到6.92％。