Effects of Wetting Behaviour on Residual Trapping in CO2-Brine Systems

Abstract

Abstract After injecting CO2 into the formations containing brine, it starts to penetrate to upper sections and will be trapped under a geological barrier, during this period the formation brine will imbibe the CO2 and some portion of it will be trapped in the pore spaces. Capillary forces prevent complete drainage of CO2 and residual saturation remains trapped in the pores. Wetting behaviour of the CO2-brine system and relative permeability to each of the phases are important modeling parameters in this phenomenon. In such a system with cycling behaviour, hysteresis in relative permeability has strong effect on trapping. There are debates on wetting behaviour of candidate formations for CO2 storage. Different wettability conditions of the formations, affect the residual trapping mechanism. In this study, theoretical concept of residual trapping is defined through flow equations, and the effect of wettability is discussed by conceptual models. To verify the theoretical concept, different wettability conditions are modeled based on the Utsira formation of Sleipner reservoir and also the Viking formation (Canadian brine formation). Hysteresis in relative permeability and capillary pressure is considered in the modeling of both cases. Results indicate that different wettability cases including strongly water wet to intermediate and slightly water wet condition, gives variation in the predicted trapped volume of CO2. This variation is from about 2 to 13% in different scenarios of this case study. Results of the simulations verify that wettability behaviour has both short and long term consequences in CO2 trapping. In low permeability simulation case, residual CO2 volume is more sensitive to the wettability condition. Results are dependent on the choice of hysteresis models but wetting behaviour of the system is the main subject that is targeted in this study.