Two Phase Flow Properties of Brine-CO2 Systems in Carbonate Core: Influence of Wettability on Pc and kr

The design of a CO₂ injection project mainly depends on the results of reservoir models. Nevertheless, it is recognized that these models generally lack physico-chemical data. This issue becomes more important for storage options, such as deep saline aquifers, for which economically driven data collection and archiving have not been performed. Among these physico-chemical data, fluid/fluid and rock/fluid interactions have been long recognized to govern fluid distribution and behavior in the porous media. This paper focuses on rock/fluid interactions with the host formation, by means of the wettability, which is one of the controlling parameters of the remaining fluid saturations, capillary pressure and relative permeability; hence conditioning the performance of any CO₂ operation.

The first part of this paper presents CO₂ and N₂ injection experiments in a carbonate core sample. Two different wettability conditions were investigated: water-wet and intermediate-wet. Thermodynamic conditions (pressure, temperature and water salinity) are representative of storage conditions and were the same for the entire core flooding experiments. Multirate experiments were conducted with in-situ saturation monitoring and enhanced interpretation workflow (heterogeneous approach) of the production curves in order to obtain relevant and complete sets of k_r and P_c data. The second part is devoted to visualization experiments. CO₂ injections were performed in glass micromodels, under the same conditions, in order to track the fluids distribution as a function of the thermodynamic and the wettability conditions.

Using this approach, we showed, on the one hand, that at the core (carbonate) and pore (micromodels) scale the CO₂ does not wet the solid surface when the porous media is water-wet. On the other hand, if the porous media presents an intermediate wettability, the CO₂ partially wets the substrate having significant effect on water mobility (k_rw). In all cases the results at the core scale were consistent with those at the pore scale.

Finally, we discuss the consequences of such CO₂ wetting behavior in terms of fluids distribution in the porous media, injectivity level and seal efficiency of the caprock since all these mechanisms have a direct impact on CO₂ storage capacity and sustainability of any prospect site.