Effect of CO2 phase on its water displacements in a sandstone core sample: experimental study

Abstract

CO2 capture and storage have been considered as a key strategy to tackle CO2 high concentrations in
the atmosphere. The captured CO2 is injected into deep saline aquifers, depleted hydrocarbon reservoirs
and coal beds as gas, liquid, and/or supercritical phase. The CO2 phase may affect its injection,
migration, and displacement efficiency. Research work on CO2 storage has mainly focused on the
trapping mechanism, risk assessment, storage site selection, etc. However, CO2 phase effect on its
injection and displacement efficiency has largely been neglected. In this paper, experimental work was
designed to investigate the impact of CO2 phase on the pressure and production profiles as the
experimental pressure increases.
The results show that CO2 phase significantly affects the differential pressure profile, relative
permeability of CO2, and residual water saturation in a sandstone core sample. The differential pressure
profiles of gaseous CO2 and supercritical CO2 phases were significantly different from that of liquid
CO2 phase, particularly before the CO2 breakthrough. The increase in the experimental pressure caused
an increase in the differential pressure profile of the sub critical CO2 phases (gaseous and liquid CO2)
but a reduction in that of the supercritical phase. The relative permeabilities of the three CO2 phases
were in the range of 11-21 % while the residual water saturations (Swr) were in the range of 36 to 42 %.
In general, the relative permeabilities of both gaseous and supercritical CO2 phases are quite close. The
relative permeabilities of liquid CO2 phase are higher. The increase in pressure caused an increase in
the relative permeability and a decline in the Swr. The scale of the change depends on CO2 phase. Thus,
our results reveal the high impact of CO2 phase on its injection, and displacements efficiency.