Deep hydrothermal systems: Mathematical modelling of hot dense brinescontaining non-condensible gases
by
Robert McKibbin
Massey University

Quantitative description of deep hydrothermal systems requires mathematical modelling of the heat and mass transfer associated with the motion of multi-component fluids in high-temperature high-pressure environments within porous rock structures. In this paper, the fluid is represented by water + sodium chloride ("brine"), with non-condensible gases represented by carbon dioxide.

The phase-space of this ternary system is four-dimensional; however, three-dimensional "cross-sections", imagined as cuts by surfaces of given non-condensible gas concentration, can be used to aid in visualising this. The resulting cross-sections are three-dimensional brine T-p-X phase sub-spaces (T is the temperature, p is the pressure and X is the mass fraction of chloride within the brine component) which are regarded as perturbations of the phase-space for the water-chloride system.

Conservation equations, together with various thermodynamic relationships and gas laws, are solved for some simple steady vertical flows. The example results provide insights into the complex relationships between the concentrations and distribution of the various components.

Date received: June 23, 1998