Thermal segregation in petroleum reservoirs
Abstract
In many petroleum reservoirs, the fluid properties are not the same through the reservoir thickness.
The variation of composition, i.e. compositional grading, can affect reserve estimation, production and EOR strategies.
One simple reason for compositional grading is the gravity force; heavy components tend to be in the lower part of the fluid column, and the light components are found in the upper part of the reservoir.
However, this is not the only reason, because there are other forces that can have an effect on the compositional grading such as thermal diffusion due to temperature gradient.
In order to determine the variations in pressure and composition with depth and to be able to indicate if/where a gas-oil contact exists, we have built a model based on the irreversible thermodynamics principles.
The model is based on the approach to thermodiffusion in porous media developed by Montel et al. [1] Using the relationships where pressure, chemical potential, and thermal gradient are linked, the distribution of chemical components in the petroleum reservoir is described.
Finally, we validate our model and calculation procedure for the compositional grading by comparing with some case studies in the literature.
[1] F. Montel, H. Hoang, and G. Galliero, “Linking up pressure, chemical potential and thermal gradients,” Eur. Phys. J. E, vol. 42, no. 5, p. 65, 2019.