CHARACTERIZATION OF PORE STRUCTURE AND DYNAMIC SEEPAGE CHARACTERISTICS OF SANDSTONE DETERMINED BY NUCLEAR MAGNETIC RESONANCE (NMR) AND MAGNETIC RESONANCE IMAGING (MRI) TECHNIQUES

The combination of nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) to investigate the seepage characteristics of sedimentary rock has been popular research in recent years. This research assessed dynamic seepage features of sandstone and shale samples through NMR and MRI measurements with two respective fluids of different wettability (i.e., distilled water and kerosene). Results show that sandstone and shale possess remarkably different T₂ spectra. The saturation of movable fluid (FFI) of the sandstone and shale samples is 75.09%, 74.92%, and 7.50%, respectively. The seepage T₂ spectra of distilled water in sandstone is predominantly bimodal distribution, whereas kerosene seepage in sandstone presents a single distribution, and those of kerosene seepage in shale show a bimodal distribution. When reaching equilibrium, the time required for kerosene seepage in sandstone is the shortest, followed by water seepage in sandstone, and kerosene seepage in shale is the longest. In addition, the fluid volumes of water and kerosene in sandstone have a strong linear relationship with time, while those of kerosene in shale have a power-function relationship. The dominant channel gradually develops and expands to both sides during the seepage process. Over time, the content of water seepage in sandstone is predominantly concentrated near the inlet, whereas the kerosene content of kerosene seepage in sandstone is primarily centered in the central region. Significant differences in unit discharge exist between the cool and warm color regions of water seepage in sandstone. However, those of kerosene seepage in sandstone are negligible.