Dynamic Occurrence and Mobilization Mechanisms of Condensate in Porous Media Revealed by Micro-CT and Two-Dimensional NMR

Abstract During the depletion of gas-condensate reservoirs, the occurrence and mobilization of condensate in porous media are far more complex than those indicated by bulk PVT experiments because of the complexity of micro- to submicron-scale pore environments, where interfacial tension, capillary forces, and adsorption jointly govern fluid behavior. Conventional single-scale experimental approaches are insufficient to reveal the underlying microscopic mechanisms. In this study, a multiscale integrated characterization framework based on micro-CT and two-dimensional nuclear magnetic resonance (2D NMR) was established. Representative high-permeability and low-permeability core samples were selected for in situ three-dimensional visualization by micro-CT and for real-time monitoring of the entire depletion process by online 2D NMR. The results show that the first detectable liquid response appears in smaller pore-size intervals and subsequently redistributes as pressure declines. In the high-permeability core observed by Micro-CT, condensate saturation increased mainly in the 40–100 and 100–350 μm intervals. In the low-permeability core monitored by NMR, the 10–40 μm response increased to an intermediate-pressure maximum and then declined. These trends are consistent with the combined effects of heterogeneous nucleation, capillary retention, pressure-driven redistribution, revaporization, and possible ripening. Because the two cores were characterized by different techniques, their curves are used to compare overall evolution trends rather than as a strict quantitative measure of permeability effects. Compared with the bulk PVT reference, the apparent porous-medium dew-point pressures and liquid dropout responses differed. These differences do not demonstrate a shift of the equilibrium phase envelope. Instead, they reflect the coupled influence of nucleation kinetics, capillarity, pore connectivity, gas–liquid flow, and the detection limits of micro-CT and NMR. The results provide a controlled core-scale description of condensate occurrence and redistribution during stepwise depletion.