School of Water Resources and Environment, China University of Geosciences (Beijing), Beijing 100083, PR China; Beijing Key Laboratory of Water Resources and Environmental Engineering, China University of Geosciences (Beijing), Beijing 100083, PR China.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):120-138. doi: 10.1166/jnn.2021.18456.
To study the changes in porosity-permeability and the characteristics of the pore structure of shale under stress and high temperature, the Lower Silurian Longmaxi Formation shale in the southern Sichuan Basin, China, was investigated under conditions of continuous pressurization and heating. In addition, the pore compression coefficients and permeability stress sensitivity coefficients were analyzed and quantified. The mineral composition of these was analyzed using scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). Our results reveal that the porosity and permeability of the shales exponentially decreases with increasing stress, reflecting that microfracture development during increasing stress causes the pores in these shale samples to enlarge. However, the pore compressibility and stress sensitivity coefficient vary for each sample, and the quantitative results indicate an overall decrease with increasing stress, suggesting that the shale deformation is nonlinear during stress release. Based on the mineral composition analyses and SEM measurements, we conclude that the nonuniform changes during stress release are related to the complexity of the shale mineral compositions and the different intercrystalline/ interlaminar pores of the different minerals, which are affected in different ways by pressure. The NMR measurements reveal that the mesopores are most developed in the shale samples, the pore volumes of the micro- and macropores are small, and the nanoscale pores are mainly from 1-60 nm in diameter. The different types of pore sizes decrease with increasing stress, indicating that the porosities measured experimentally reflect the synergistic effects of the different pore sizes on porosity. As the temperature increases, the permeability of the shale decreases significantly, which is primarily caused by the thermal expansion effect. The high clay mineral content of the shales also causes their permeabilities to be sensitive to temperature.
为了研究应力和高温下页岩的孔隙度-渗透率变化和孔隙结构特征，对中国四川盆地南部下志留统龙马溪组页岩进行了连续加压和加热条件下的研究。此外，还分析和量化了孔隙压缩系数和渗透率应力敏感性系数。采用扫描电子显微镜（SEM）和核磁共振（NMR）对这些页岩的矿物组成进行了分析。我们的研究结果表明，页岩的孔隙度和渗透率随应力的增加呈指数下降，这反映了在增加应力的过程中微裂缝的发育导致这些页岩样品中的孔隙扩大。然而，每个样品的孔隙压缩性和应力敏感性系数都有所不同，定量结果表明随着应力的增加而总体下降，这表明在应力释放过程中页岩的变形是非线性的。基于矿物成分分析和 SEM 测量，我们得出结论，应力释放过程中的不均匀变化与页岩矿物成分的复杂性以及不同矿物之间的不同晶间/层间孔隙有关，这些孔隙受到压力的不同影响。NMR 测量结果表明，页岩样品中最发达的是中孔，微孔和大孔的孔体积较小，纳米级孔主要分布在 1-60nm 直径范围内。不同类型的孔径随应力的增加而减小，这表明实验测量的孔隙度反映了不同孔径对孔隙度的协同作用。随着温度的升高，页岩的渗透率显著降低，这主要是由于热膨胀效应。页岩中高含量的粘土矿物也使其渗透率对温度敏感。
