Mathematical Modelling of Non-Condensible Gases in Hot Dense Brines: the System H2O-NaCl-CO2

Abstract

Previous work investigating models which describe the behaviour of brine systems (water + sodium chloride) at high temperatures and pressures is extended to include the presence of non-condensible gases. It is assumed in the model equations that the gases are represented by carbon dioxide. The consequent system is supposed to have the basic characteristics of a brine system as previously studied but with a non-condensible gas added. The phase-space of this ternary system is four-dimensional; however, three-dimensional "cross-sections", imagined as cuts by surfaces of given C02 concentration,can be used to aid in visualising this. The resulting cross-section is a three-dimensional brine T-p-X phase subspace. The characteristics of the various regions of this 3-D phase-space (McKibbin & McNabb, 1993) are presumed to still apply, but the boundaries are altered in position owing to the presence of the Conservation equations are derived; these, together with various thermodynamic relationships and gas laws, are solved for some simple steady vertical flows. The example results provide some insights into the complex relationships between the concentrationsof the various components.