Phase Behavior and Composition Distribution of Multiphase Hydrocarbon Binary Mixtures in Heterogeneous Nanopores: A...

Area of Science:

• Petroleum Geoscience
• Materials Science
• Computational Chemistry

Background:

• Unconventional reservoirs contain complex nanoporous structures.
• Understanding fluid behavior in nanopores is crucial for accurate reservoir simulation.
• Heterogeneity in pore size and wettability influences fluid distribution.

Purpose of the Study:

• To investigate the phase behavior and composition distribution of ethane/heptane mixtures in heterogeneous oil-wet graphite nanopores.
• To determine the impact of nanopore confinement and pore size distribution on hydrocarbon mixtures.
• To provide insights for improving macro-scale reservoir simulations.

Main Methods:

• Molecular dynamics (MD) simulations were employed.
• Simulations were conducted on connected bulk and nanopore systems (5-nm and 2-nm pores).
• Analysis focused on phase equilibrium and molecular distribution within the nanopores.

Main Results:

• Nanopore confinement significantly influences phase equilibrium, with stronger effects in smaller pores.
• Multiple adsorbed layers of hydrocarbon molecules were observed near pore surfaces.
• For 2-nm pores, hydrocarbon molecules were predominantly in the adsorbed phase.
• The overall composition of the hydrocarbon mixture was found to be dependent on pore size.

Conclusions:

• Heterogeneous shale nanopores host fluids with varying compositions based on pore size.
• Current macro-scale reservoir simulations may contain significant errors due to simplified composition calculations.
• Modifications to the calculation of overall composition in shale nanopores are necessary for accurate recovery estimations.