Luo Xiangzhong, Wang Chaolin, Zhao Yu, Ning Lin, Shen Mingxuan
College of Civil Engineering, Guizhou University, Guiyang, Huaxi District, 550025, Guizhou, China.
Sci Rep. 2025 Feb 20;15(1):6184. doi: 10.1038/s41598-025-89480-5.
Understanding the spontaneous water imbibition mechanism in coal of varying ranks has substantial implications for hydraulic operations and the safe, efficient extraction of coalbed methane. During spontaneous imbibition, low-field nuclear magnetic resonance techniques were used to test the T spectra and imaging (MRI) of coal samples, enabling the determination of water signal distribution in the samples at different time intervals. By combining this with the pore structure, we explored the water migration characteristics of the coal samples during spontaneous imbibition from a microscopic perspective. Additionally, we deeply investigated the relationship between the MRI pixel eigenvalues, the capillary absorption coefficients, and the degree of pore development. The results demonstrated a positive correlation between the capillary water absorption coefficient and the degree of pore development in the coal samples, while revealing a negative correlation with both pore diameter and tortuosity. In the process of spontaneous imbibition, micropores exert a dominant influence and achieve saturation first, followed by a gradual increase in the contribution of mesopores and macropores (including microfractures) to spontaneous imbibition. The MRI results demonstrate that water migration primarily occurs within the interior of the coal samples before extending towards the exterior. The pixel values obtained from MRI follow a normal distribution, with the mean value reflecting the extent of pore development and the entropy representing the randomness in pore distribution. The higher the pixel eigenvalue, the greater the pore content of the coal sample, indicating a more random distribution of pores and enhanced connectivity among various types of pores, which results in an increased capillary water absorption coefficient.
了解不同煤阶煤的自发吸水机制对水力作业以及煤层气的安全、高效开采具有重要意义。在自发吸水过程中，利用低场核磁共振技术对煤样进行T谱测试和成像（MRI），从而确定不同时间间隔下煤样中的水信号分布。通过将其与孔隙结构相结合，从微观角度探究了煤样在自发吸水过程中的水迁移特性。此外，我们深入研究了MRI像素特征值、毛细吸收系数与孔隙发育程度之间的关系。结果表明，煤样的毛细吸水系数与孔隙发育程度呈正相关，而与孔径和曲折度呈负相关。在自发吸水过程中，微孔起主导作用并首先达到饱和，随后中孔和大孔（包括微裂缝）对自发吸水的贡献逐渐增加。MRI结果表明，水迁移主要发生在煤样内部，然后向外部扩展。从MRI获得的像素值呈正态分布，其平均值反映孔隙发育程度，熵表示孔隙分布的随机性。像素特征值越高，煤样的孔隙含量越大，表明孔隙分布越随机，各类孔隙之间的连通性增强，从而导致毛细吸水系数增加。
