Molecular dynamics simulations of NMR relaxation and diffusion of hydrocarbons

NMR (Nuclear magnetic resonance) is widely used as a logging tool in reservoir exploration and provides information on pore size distribution, fluid distribution, and insights into wettability. Towards better utilizing NMR log data, it is essential to assess the current models of NMR relaxation. To this end, we explicitly calculate the NMR dipole-dipole relaxation in model hydrocarbons and water for single state points and dipole-dipole and spin-rotation relaxation in methane for a range of state-points spanning the vapor, super-critical, and liquid phases. We can successfully predict ¹H NMR T1,2 relaxation and diffusion, but the relaxation behavior siginificantly deviate from those based on classical hard sphere models that are often used to interpret the relaxation behavior.