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

Abstract

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 kr and Pc 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 (krw). 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. Introduction In CO2 geological storage projects, two critical issues must be addressed to make sure that this process is a secure and feasible strategy to stabilize carbon dioxide concentration in the atmosphere: the location and distribution of the injected CO2 in the reservoir, and the demonstration that it will remain stored in the long term; that has been defined by the IEA-GHG1 as a period ranging from several hundreds to several thousands years. The first issue refers to CO2 behavior in the reservoir rock and the second to its eventual invasion of the caprock, a low permeable and usually shaly porous material saturated with water. This paper addresses the effects of different wettability scenarios on both issues. Wettability is defined as the tendency of one fluid to spread on or adhere to a solid surface in the presence of other immiscible fluids.2 In the case of a CO2 flooding operation; it determines the fluid distribution in the reservoir because it affects the quantity displaced as well as how the displacement proceeds. When displaced, the wetting fluid will occupy the small pores and will be present in the largest pores as a film on the rock surface. The existence of such a film enhances the continuity of the wetting phase, affecting the petrophysical properties of the reservoir; among them the relative permeability and the capillary pressure curves, and therefore the injectivity level associated to a reservoir formation.3 * Now with Gaz de France (GdF)

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CO2 Adhesion on Hydrated Mineral Surfaces

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