Key Laboratory of Computational Geodynamics, College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
China United Coalbed Methane Co. Ltd., Beijing 100015, China.
J Nanosci Nanotechnol. 2021 Jan 1;21(1):234-245. doi: 10.1166/jnn.2021.18743.
The complex pore system in tight sandstone reservoirs controls the storage and transport of natural gas. Thus, quantitatively characterizing the micro-nanopore structure of tight sandstone reservoirs is of great significance to determining the accumulation and distribution of tight gas. The pore structure of reservoirs was determined through polarizing microscopy, scanning electron microscopy (SEM), and the combination of mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) experiments on Late Paleozoic conventional and tight sandstone samples from the Linxing Block, Ordos Basin. The results show that in contrast to conventional sandstone, dissolution pores, with diameters less than 8 μm, are the main contributors to the gas storage space of tight sandstone reservoirs. The pore size distribution derived from the MICP experiment demonstrates that the main peak of tight sandstones corresponds to a pore radius in the range of 247 nm to 371 nm, while the secondary peak usually corresponds to 18 nm. The results of the NMR test illustrate that the ₂ spectra of tight sandstones are unimodal, bimodal and multimodal, and the main NMR peak is highly related to the MICP peak. Fractal theory was proposed to quantitatively characterize the complex pore structure and rough porous surface. The sandstones show fractal characteristics including nanopore fractal dimension obtained from the MICP and large pore fractal dimension obtained from the NMR experiment. Both and are positively correlated with porosity and negatively correlated with permeability, demonstrating that complex and heterogeneous pore structure could increase the gas storage space and reduce the connectivity.
致密砂岩储层中的复杂孔隙系统控制着天然气的储存和运移。因此，定量刻画致密砂岩储层的微纳米孔隙结构对于确定致密气的聚集和分布具有重要意义。通过对鄂尔多斯盆地临兴区块晚古生代常规砂岩和致密砂岩样品进行偏光显微镜、扫描电子显微镜（SEM）以及压汞和核磁共振（NMR）实验的组合，确定了储层的孔隙结构。结果表明，与常规砂岩相比，直径小于 8μm 的溶解孔隙是致密砂岩储层储气空间的主要贡献者。压汞实验得到的孔径分布表明，致密砂岩的主要峰值对应于 247nm 至 371nm 的孔径范围，而次峰值通常对应于 18nm。NMR 测试结果表明，致密砂岩的 ₂谱呈单峰、双峰和多峰，主要 NMR 峰与压汞峰高度相关。分形理论被提出用于定量刻画复杂的孔隙结构和粗糙的多孔表面。砂岩具有分形特征，包括压汞得到的纳米孔分形维数 和 NMR 实验得到的大孔分形维数 。和 都与孔隙度呈正相关，与渗透率呈负相关，表明复杂和不均匀的孔隙结构可以增加储气空间，降低连通性。
