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OLIVEIRA, E. L. Nuclear spin diffusion in porous media – a computational approach of NMR. 2015. 143 p. Dissertação (Mestrado em Ciências) Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, 2015. Nuclear Magnetic Resonance (NMR) is a versatile technique applied in many different areas of science such as Physics, Chemistry and Medicine. Several important NMR works applied in the study of the molecular dynamics of fluids inside porous media allowed this technique to become popular in the oil industry. This project is based on some of these seminal works. Using computational physics models, the main physical effects of diffusion and relaxation for the nuclear spins in an ensemble of molecules in a fluid permeating the porous media are reproduced. The theoretical methods used to interpret the transverse (T2) and longitudinal (T1) relaxation parameters take into consideration the macroscopic dynamical properties of an ensemble of nuclear spins. In order to comprehend the diffusion and relaxation in porous media, the use of computational physics methods that take into account the translational diffusion of the nuclear spins inside the media as well as its microstructure is essential. In the proposed models by this dissertation, basic statistical mechanics and nuclear relaxation concepts were used, resulting in programs that demand considerable computational resources. For the numerical simulations it was necessary to digitally construct the microstructure of the porous media and that was achieved with the use of X-ray 3D microtomography. On this digital microstructure, the diffusion process and the resulting relaxation of the nuclear spins were simulated with random walk models, an example of the Monte Carlo Method. The numerical simulation of classic NMR experiments, such as the one used to determine the distribution of relaxation times (known as CPMG), and more advanced ones, such as the one used to determine exchange rates between different sites (2D exchange experiments), produced fundamental results to the understanding of the fluid dynamics in porous media.

Difusão de spins nucleares em meios porosos - uma abordagem computacional da RMN