Pore scale phase behavior of condensate gas in porous media: Insights from 2D NMR T₁–T₂ spectrum method

The widespread development of unconventional oil and gas reservoirs has advanced reservoir research to the nanoscale level. Under the influence of nanoscale confinement effects, the phase behavior of condensate gas reservoirs deviates from the classical theories derived from traditional pressure/volume/temperature (PVT) experiments. Therefore, studying the phase behavior of fluids in porous media at the nanoscale is significant. The experiment employs two-dimensional nuclear magnetic resonance T₁–T₂ (2D NMR T₁–T₂) spectrum method to study the phase behavior characteristics of condensate gas in three cores with varying degrees of tightness, then explores the effects of different cores and different CO₂ contents on the phase behavior characteristics of condensate gas. As the core tight degrees of cores increases, the dew point pressure rises from 25.9 to 27.9 MPa while restricting fluid migration within the pores. The maximum condensate oil saturation increases from 10.35% to 17.35%. Compared with the bulk PVT phase experiment, the dew point pressure of condensate gas in porous media is lower than that of condensate gas in the PVT visualization cell. This is related to the formation of phase mixing and “liquid bridges” when oil and gas reach the dew point pressure in porous media. The retrograde condensation phenomenon in condensate gas systems in different porous media occurs first in the micropores. CO₂ inhibits the retrograde condensation phenomenon in tight cores, and CO₂ concentration is negatively correlated with the dew point pressure of the condensate gas.