Hello!

I’m creating a model to simulate the disposal of highly saline (TDS on the order of 200,000mg/L) oil field brines in deep aquifers, necessitating the use of a density-dependant model.

I’m trying to better understand the density ratio parameter and how it is used to calculate the density of fluids that fall between maximum solute concentration (Cs) and reference concentration (Co). Does FEFLOW assume that fluid density increases linearly with increasing solute concentration? Or does it have some built-in equation that relates concentration to density, and, if so, where might I find more information on it?
The density ratio alpha is calculated by [b]alpha = (maximum density - minimum density) / minimum density[/b]. The maximum density refers to the density of the fluid with the maximum concentration [b]C[sub]S[/sub][/b] and the minimum density corresponds to the fluid density with the reference concentration [b]C[sub]0[/sub][/b]. This simple relationship is rather linear.

FEFLOW has different ways to consider density variations in the governing equations you are solving:
[list]
[li]Buoyancy gravity-related terms. All density-variations are neglected apart from the crucial buoyancy terms within the Darcy equation[/li]
[li]Buoyancy, gradient, and rate-of-change terms. Density variations are additionally considered in the balance terms[/li]
[li]Buoyancy, gradient, rate-of-change and fluid disperse terms[/li]
[/list]
More details are provided by the following White Papers:

White Paper I, Chapter 7
White Paper I, Chapter 17
White Paper II, Chapter 1