Structural and Nuclear Magnetic Resonance Relaxation Properties of Shale Condensate within Organic Nanopores via Molecular Dynamics Simulations

We conducted a series of molecular dynamics (MD) simulations to investigate the molecular structure, dynamics, and nuclear magnetic resonance (NMR) relaxation of multicomponent shale condensate confined within kerogen nanopores. Detailed analysis of the mean-squared displacements (MSD), diffusion coefficients (D A), and NMR relaxations times was carried out on each component of the shale condensate as a function of pore size, pressure, and Larmor frequency. Simulations show that kerogen–fluid interactions strongly affect the dynamic behavior of shale condensate when the size of the pore is reduced from 29 to 3 nm. Additionally, the results indicate that pressure plays an important role in the diffusion and relaxation of each condensate component inside kerogen nanopores. MSD analysis shows that the mobility of each molecular compound decreases as the molecular weight increases. MD results also indicate that the branched-chain hydrocarbons (isobutane and isopentane) exhibit higher diffusivity compared to n-butane and n-pentane species. Furthermore, diffusion coefficients, obtained via Einstein’s relation, decrease as the pore size decreases and pressure increases. NMR relaxation times of each compound of shale condensate are affected by confinement and pressure. To quantify the contribution of Larmor’s frequency to the NMR relaxation properties, we computed the longitudinal relaxation time (T 1) for three different Larmor frequencies (2.3, 22, and 400 MHz). At higher frequencies, lighter shale condensate components exhibit longer longitudinal relaxation times compared to the heavier components. These results contribute to a deeper understanding of the dynamic and NMR behavior of shale condensate confined in kerogen nanopores.