Phase Behavior and Dew Point Pressure of Multicomponent Condensate Gas in Nanopores

Shale gas reservoirs typically contain numerous nanoscale pores, with pore size playing a significant role in influencing the gas behavior. To better understand the related mechanisms, this study employs the GaugeGEMC molecular simulation method to systematically analyze the effects of various pore sizes (5, 10, 20, and 40 nm) on the phase behavior and dew point pressure of the shale gas reservoir components. The simulation results reveal that when pore sizes are smaller than 40 nm, the dew point pressure increases significantly as the pore size decreases. For instance, the dew point pressure in 5 nm pores is 20.3% higher than under macroscopic conditions. Additionally, larger hydrocarbon molecules exhibit a tendency to aggregate in smaller pores, particularly in the 5-10 nm range, where the relative concentration of heavy hydrocarbons (C4+) increases markedly. Moreover, as the pore size becomes larger, the component distribution gradually aligns with experimental results observed under macroscopic conditions. This study demonstrates that pore effects are more pronounced for smaller sizes, directly influencing the aggregation of heavy hydrocarbons and the rise in dew point pressure. These phenomena could significantly impact the diffusivity of shale gas reservoirs and the recovery of condensate gas. The findings provide new theoretical insights into phase behavior changes in nanopores, offering valuable guidance for optimizing shale gas reservoir extraction strategies.