Abstract Shale reservoirs can be stimulated by injecting cryogenic fluids such as liquid nitrogen (LN2) to initiate and propagate fractures and to connect existing natural fracture networks. This research aims to investigate the efficacy of the cryogenic treatments on the porosity, permeability, and mechanical properties (Young's modulus, Poisson's ratio, brittleness, bulk compressibility, and unconfined compressive strength (UCS)) of Marcellus downhole core samples. Three downhole core samples, taken from 1700 m depth, were heated up to the reservoir temperature (66 °C). LN2 was then injected into a core holder hosting the core samples. Then, the samples were pressurized at three different pressures of 1.38, 2.76, and 4.14 MPa. Computed tomography (CT) scan, porosity, permeability, and ultrasonic velocity tests were conducted on the core samples prior to and after implementing the cryogenic treatments. The results of the CT-scan analyses, porosity, permeability, and mechanical property measurements revealed that implementing the cryogenic treatments resulted in creating new cracks in all the core samples. The results also demonstrated that pressurizing the injected LN2 at 1.38, 2.76, and 4.14 MPa increased the porosities of the core samples by 1.51%, 2.49%, and 5.01% and significantly increased the permeability by 270%, 388%, and 9482%, respectively owing to the creation of new cracks inside the core samples. Also, the compressional and shear velocities decreased owing to the creation of the new cracks resulted from conducting the cryogenic treatment by up to 2.11% and 0.70%, respectively. As a result, dynamic Young's modulus and Poisson's ratio of the core samples decreased by up to 2.37% and 5.24%, respectively. Moreover, the brittleness and bulk compressibility increased by up to 1.59% and 7.05%, respectively. After implementing the cryogenic treatments, the UCS of the core samples ranged from 34.73 to 2.57 MPa, significantly lower than typical values of UCS for Marcellus core samples (101–170 MPa), owing to the creation of new cracks resulting from implementing the cryogenic treatments. The results revealed that the cryogenic treatments could be potentially implemented in shale fields to increase the permeability, and as a result, increase hydrocarbon production rates.

中文翻译：

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低温处理对 Marcellus 井下岩心样品孔隙度、渗透率和力学性能影响的实验研究

摘要 页岩储层可以通过注入液氮 (LN2) 等低温流体来激发和扩展裂缝并连接现有的天然裂缝网络来增产。本研究旨在研究低温处理对 Marcellus 井下岩心样品的孔隙率、渗透率和力学性能（杨氏模量、泊松比、脆性、体积压缩性和无侧限抗压强度 (UCS)）的影响。取自 1700 m 深度的三个井下岩心样品被加热到储层温度 (66 °C)。然后将 LN2 注入装有岩心样品的岩心支架中。然后，在 1.38、2.76 和 4.14 MPa 的三个不同压力下对样品加压。计算机断层扫描 (CT) 扫描、孔隙率、渗透率、在实施低温处理之前和之后，对岩心样品进行了超声波速度测试。CT 扫描分析、孔隙度、渗透率和机械性能测量的结果表明，实施低温处理导致在所有岩心样品中产生新裂缝。结果还表明，将注入的 LN2 加压到 1.38、2.76 和 4.14 MPa 使岩心样品的孔隙度增加了 1.51%、2.49% 和 5.01%，并且渗透率显着增加了 270%、388% 和 9482%，分别是由于在岩心样品内部产生了新的裂缝。此外，由于进行低温处理导致新裂纹的产生，压缩和剪切速度分别降低了 2.11% 和 0.70%。因此，充满活力的 Young' 岩心样品的 s 模量和泊松比分别下降了 2.37% 和 5.24%。此外，脆性和体积压缩率分别增加了 1.59% 和 7.05%。实施深冷处理后，岩心样品的 UCS 范围为 34.73 至 2.57 MPa，显着低于 Marcellus 岩心样品的 UCS 典型值（101-170 MPa），这是由于实施深冷处理产生了新的裂缝. 结果表明，低温处理有可能在页岩油田中实施以增加渗透率，从而提高油气产量。分别。实施深冷处理后，岩心样品的 UCS 范围为 34.73 至 2.57 MPa，显着低于 Marcellus 岩心样品的 UCS 典型值（101-170 MPa），这是由于实施深冷处理产生了新的裂缝. 结果表明，低温处理有可能在页岩油田中实施以增加渗透率，从而提高油气产量。分别。实施深冷处理后，岩心样品的 UCS 范围为 34.73 至 2.57 MPa，显着低于 Marcellus 岩心样品的 UCS 典型值（101-170 MPa），这是由于实施深冷处理产生了新的裂缝. 结果表明，低温处理有可能在页岩油田中实施以增加渗透率，从而提高油气产量。