Simulation Of Multi-dimensional NMR Detection And Microcosmic Responses For Shale Rocks

Nuclear magnetic resonance (NMR) is a new technique which can evaluate the distribution of pore fluid in rock space. In conventional sandstone and carbonate formations, nuclear magnetic resonance can not only obtain conventional parameters such as porosity and permeability,but also realize porosity Fluid identification and reservoir evaluation. However, in the detection of shale reservoirs, shale NMR is facing some problems, because of shale has a pore size of nano-scale,mineral composition is very complex, organic matter is high and the internal magnetic field exists during measurement,Low resolution ratio and model in the shale reservoir is not applicable. Therefore, the study of shale multidimensional NMR detection and microscale response is of great significance to evaluate shale pore structure.Based on the numerical simulation of nuclear magnetic resonance, the microcosmic response of nuclear magnetic resonance model based on the reconstruction of digital core model and X - ray CT scanning based on diagenetic process is builded. Firstly, based on the sedimentary mechanism of sedimentary rocks,the deposition process of sedimentary rocks is simulated and the three-dimensional digital cores are reconstructed to produce ideal digital core models with different porosity. Secondly, the numerical simulation of nuclear magnetic resonance (NMR) is carried out on the three-dimensional digital core of ideal model. The one-dimensional and two-dimensional microscopic response of nuclear magnetic resonance (NMR) is studied by changing the compaction degree and filling different water saturation.Then, using X-ray CT scanning technique, high-resolution CT scanning experiment was carried out to generate three nano-scale three-dimensional shale digital cores, and the shale CT images were reconstructed by AVIZO software to divide the mineral composition. Finally,based on the three-dimensional digital core of the shale,the one-dimensional and two-dimensional numerical simulation of the digital core magnetic resonance of the shale is carried out and the microcosmic response is explored.The results show that the degree of limited diffusion of digital cores with different resolution is increasing with the increase of resolution. In the process of simulated diagenesis, as the degree of compaction increases, the porosity of the ideal digital core becomes smaller, the amplitude of its T2 spectrum will be significantly reduced, and the T2 distribution will move in the short relaxation time direction. It is found that the signal of the wetting fluid in the T2-D distribution deviates from its free diffusion coefficient line with the decrease of the wetting phase saturation by the numerical simulation of the NMR of the digital core containing the saturated fluid with different wetting phases. In the process of microscopic numerical simulation of microstructure of shale, with the increase of echo interval, the T2 distribution and shape have changed obviously and are in the right direction, and because of the higher resolution of shale core, So the restricted diffusion of the wetting fluid is more pronounced.