Molecular diffusion in systems related to reservoir fluids
Molecular diffusion is a vital mass transport phenomenon for a system to transit from a non-equilibrium state to an equilibrium one. It is a slow process compared to convection but can be crucial in many areas, including geological processes, chemical reaction and separation processes, and biomedical applications. Diffusion can become a critical mass transfer mechanism that directly influences the production from petroleum reservoirs, e.g., in solution-gas drive, recovery of trapped oil, development of naturally fractured reservoirs, and production from unconventional tight formations. It also significantly affects subsurface processes like geological CO2 sequestration and underground hydrogen storage. In this study, we intend to improve the understanding and description of molecular diffusion in reservoir fluids-related systems at elevated pressures. Studying these high-pressure mixtures will also benefit CO2 sequestration and underground H2 storage.
The reservoir fluids-related systems are mostly hydrocarbon mixtures with relatively more studies than many other systems. Nevertheless, there is still a significant knowledge gap in experimental data and modeling for these systems' diffusion coefficients. In this study, we have tried to form a more systematic understanding of molecular diffusion in reservoir fluids-related systems through efforts in three aspects.
First, we made a systematic review of the available data for reservoir fluids-related systems as well as a comprehensive comparison of commonly used correlations for hydrocarbon mixtures. We collected extensive data of diffusion coefficients in binary mixtures related to petroleum fluids and established a database of over 80 binaries and 1600 data points. We also collected over 400 data points for gas diffusion in different oils and reservoir fluids. Second, we established a self-designed set-up for measuring high-pressure diffusion coefficients for oil systems. We measured the diffusion coefficients for methane in different n-alkanes, as well as diffusion coefficients of methane/ethane in two live oils. Finally, we worked on the simulation of the one-dimensional diffusion process in the CVD experiment.
We have gained a deeper understanding of molecular diffusion in reservoir fluids-related systems through the research in the three aspects mentioned earlier. We have obtained a more systematic evaluation of the data availability and the performance of different correlations, which help us to define future research topics like what systems to measure and how to improve the correlations. The CVD experimental set-up established here will facilitate the future measurement of high-pressure diffusion coefficients. Finally, the improved CVD simulation code will benefit the data interpretation of CVD tests and even other diffusion processes.
Principal Supervisor:
Associate Professor Wei Yan, DTU Chemistry
Co-supervisor:
Professor Erling Halfdan Stenby, DTU Chemistry
Associate Professor Alexander Shapiro, DTU Chemical Engineering
Examiners:
Professor Nicolas von Solms, DTU Chemical Engineering
Professor Birol Dindoruk, University of Houston, USA
Senior specialist Tao Yang, Equinor, Norway
Chairperson:
Senior Researcher Dennis Larsen, DTU Chemistry