CO2 Sequestration

[Relative Permeability; Residual Saturation; Wettability]

1. As the properties of CO2-phase vary considerably from that of an oil-phase, unlike an oil-water system, to what extent, the relative permeability of a CO2-brine system is expected to differ?

In such cases, to what extent, the elevated IFT (capillary forces) and the lower viscosity ratio (viscous forces) in a CO2-brine system – would influence the resulting residual saturation in pores?

Further, can we capture the incomplete brine displacement by CO2 – leading to an elevated residual brine saturation - resulting from (a) ‘CO2 channeling’ caused by heterogeneity of rock sample; and (b) ‘fingering’ caused by mobility ratio?

Whether conventional constitutive models remain to be sufficient – towards predicting relative-permeability and capillary pressure - under dynamic, long-term wettability alteration – associated with a CO2-brine system? In such systems, how exactly to capture the hysteresis and scanning curves caused by a wettability gradient in space?

Or,

a relative simpler, instantaneous wettability alteration in the relative permeabilities would suffice?

In either case, how to go about - upscaling the pore-scale time-dependent wettability alteration process - connected to the capillary pressure function?

2. Whether the suppressed endpoint relative permeability values of CO2 (generally, less than 0.3); and the elevated endpoint relative permeability value of residual saturation brine (mostly, greater than 0.4) has any field relevance?

Whether the shifting of relative permeability curves – caused by the low viscosity of CO2 – remains responsible - for an elevated brine saturation @ laboratory-scale experiments - using core samples?

Can we rule out gravity-segregation (which causes vertical heterogeneity of saturation resulting from simultaneous ‘upward movement of CO2’ and ‘downward movement of brine’) and the ‘capillary end effect’ (capillary pressure getting vanished @ the end of the core sample, upon enhancing the saturation of wetting-phase) in such cases?

3. If wettability is not assumed to be static in time and uniform in space, then, to what extent, the efficiency of CO2 injection – remains influenced by the ‘wettability’ behavior of a CO2-brine system – given the fact that – wettability remains to be a dynamic process, which depends on surface chemistry, exposure time, composition of fluids and reservoir pressure & temperature?

Whether a relatively ‘stronger water-wet’ ‘CO2-brine system’ – would bring down – ‘CO2 injection efficiency’?

4. How about the dependency of relative permeability of CO2/brine on (a) flow rate changes; and on (b) residual brine saturation – considering the effects of capillary and viscous forces? Or, what exactly causes a model that remains to be dependent on saturation-time paths generated by the respective drainage-imbibition cycle?

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