Research on the Influence of NMR Acquisition Parameters on Fluid Distribution in Shale Reservoirs

Unconventional reservoirs are confronted with numerous challenges due to their complex pore structures and diverse fluid occurrence states; therefore, the accurate acquisition of pore structure characteristics and fluid property parameters has become the key factor restricting development efficiency. 2D nuclear magnetic resonance (NMR) logging obtains more observation information by introducing longitudinal relaxation time (T₁), and it exhibits good application effects in wettability evaluation, reservoir parameter calculation and fluid property identification .The factors affecting NMR relaxation signals are multivariate, mainly including pore fluid properties (viscosity, density, etc.), pore structure characteristics (pore size and distribution, pore connectivity, etc.), magnetic susceptibility differences between rocks and fluids, and the content and distribution of paramagnetic minerals. The coupling of these factors complicates the mapping relationship between relaxation signals and reservoir properties, which urgently requires in-depth analysis.In the field of shale oil exploration and development, there are various types of 2D NMR instruments, and significant differences exist in their observation methods, measurement sequences and acquisition parameters, which further pose challenges to the cross-scale characterization and comprehensive interpretation of reservoir parameters. Therefore, this study analyzes the influencing factors of acquisition parameters on NMR from both experimental and numerical simulation scales.The influence of instrument frequency on 2D NMR is investigated through experiments, and the effects of echo spacing, waiting time and number of echoes on NMR measurement and inversion results are studied via numerical simulation. This research further clarifies the influence of acquisition parameters on fluid distribution characterized by 2D NMR, and verifies the reliability of NMR logging interpretation data in shale reservoirs.