Thermodiffusion in multicomponent n-alkane mixtures.

Area of Science:

• Geochemistry
• Physical Chemistry
• Petroleum Engineering

Background:

• Compositional grading in hydrocarbon mixtures influences pre-exploitation evaluations.
• Thermodiffusion, driven by geothermal gradients, causes species separation in reservoirs.
• Measuring and modeling thermodiffusion in multicomponent mixtures remains challenging.

Purpose of the Study:

• Investigate thermodiffusion in multicomponent n-alkane mixtures at high pressures.
• Quantify the impact of thermodiffusion on initial fluid distribution in reservoirs.

Main Methods:

• Experimental measurements of thermodiffusion in microgravity (Shi Jian 10 spacecraft) to prevent convection.
• Molecular dynamics simulations to confirm experimental observations.
• Analysis of condensate gas data to model reservoir fluid distribution.

Main Results:

• Lightest and heaviest n-alkane species migrated to hot and cold regions, respectively.
• Experimental trends were validated by molecular dynamics simulations.
• Thermodiffusion was found to counteract gravitational segregation in idealized reservoir models.

Conclusions:

• Thermodiffusion significantly influences the vertical distribution of species in reservoirs.
• The effect of thermodiffusion can lead to unstable fluid columns.
• Accurate thermodiffusion data for multicomponent mixtures are essential for evaluating initial reservoir fluid states.