The phase behaviour modelling of gaseous/super critical CO2 mixtures with reservoir brine exhibits constraints regarding thermodynamical complexity of the system as well as insufficiencies in computing approaches. The modelling of physical properties of mixtures of CO2 with CH4 in a depleted gas reservoir is not problematic. In this study a generic reservoir model was created with the aid of a commercial reservoir simulator ECLIPSE, which uses different approaches on modelling the phase behaviour of CO2 containing geological systems. The model reservoir, adapted to storage properties of real cases, was assumed to be infinite acting, homogenous and isothermal. A constant rate of CO2 injection was considered. The critical saturation for the flow of gas and water, salinity and brine composition as well as the permeability anisotropy were defined as main parameters influencing the solution trapping of CO2. The chemical interactions between the system components as well as the hysteresis effects of mechanical trapping were neglected.

The phase/solubility calculations are most critical for the prediction of solution trapping capacity of the aquifers. The migration capacity of the higher density plumes is dependent on the solubility modelling of CO2 in brine. The results indicate an obvious sensitivity to the varying solubility of CO2 in various types of brines (NaCl, CaCl2) with changing salinities. The ratio of vertical to horizontal permeability (kv/kh) has a significant effect; at low kv/kh CO2 tends to migrate laterally, whereas an increase in this ratio enhances the vertical gas migration leading to more CO2 dissolution trapping.

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