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NPJ Microgravity. 2017 Aug 11;3:20. doi: 10.1038/s41526-017-0026-8. eCollection 2017.

Thermodiffusion in multicomponent n-alkane mixtures.

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Laboratoire des Fluides Complexes et leurs Réservoirs-IPRA, E2S, UMR5150, Univ Pau & Pays Adour/CNRS/TOTAL, 64000 Pau, France.
Centre National d'Etudes Spatiales (CNES) 2, Place Maurice Quentin, 75001 Paris, France.
Laboratoire de Chimie-Physique, UMR 8000 CNRS, Université Paris-Sud, Orsay, France.
Department of Earth Science and Engineering, Imperial College London, London, UK.
MGEP Mondragon GoiEskola Politeknikoa, Mechanical and Industrial Manufacturing Department, Mondragon, Spain.
Departamento de Física Aplicada I. Universidad Complutense, Madrid, Spain.
Key Laboratory of Microgravity, Institute of Mechanics, Chinese Academy of Science, Beijing, China.
State Key Laboratory of Enhanced Oil Recovery (Research Institute of Petroleum Exploration & Development), CNPC, Beijing, China.
TOTAL Exploration Production, Pau, France.
European Space Agency, ESTEC, Noordwijk, The Netherlands.


Compositional grading within a mixture has a strong impact on the evaluation of the pre-exploitation distribution of hydrocarbons in underground layers and sediments. Thermodiffusion, which leads to a partial diffusive separation of species in a mixture due to the geothermal gradient, is thought to play an important role in determining the distribution of species in a reservoir. However, despite recent progress, thermodiffusion is still difficult to measure and model in multicomponent mixtures. In this work, we report on experimental investigations of the thermodiffusion of multicomponent n-alkane mixtures at pressure above 30 MPa. The experiments have been conducted in space onboard the Shi Jian 10 spacecraft so as to isolate the studied phenomena from convection. For the two exploitable cells, containing a ternary liquid mixture and a condensate gas, measurements have shown that the lightest and heaviest species had a tendency to migrate, relatively to the rest of the species, to the hot and cold region, respectively. These trends have been confirmed by molecular dynamics simulations. The measured condensate gas data have been used to quantify the influence of thermodiffusion on the initial fluid distribution of an idealised one dimension reservoir. The results obtained indicate that thermodiffusion tends to noticeably counteract the influence of gravitational segregation on the vertical distribution of species, which could result in an unstable fluid column. This confirms that, in oil and gas reservoirs, the availability of thermodiffusion data for multicomponent mixtures is crucial for a correct evaluation of the initial state fluid distribution.

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