Experimental study of the effect of variation in in-situ stress on capillary residual trapping during CO ₂ geo-sequestration in sandstone reservoirs

During a geo-sequestration process, CO ₂ injection causes an increase in reservoir pore pressure, which in turn decreases the reservoir net effective stress. Changes in effective stress can change all the reservoir and cap-rock properties including residual saturations. This article presents the results of an experimental work carried out to understand the potential change in the volumes of residually trapped CO ₂, while the porous medium tested underwent change in the net effective stress under in-situ reservoir conditions of pore pressure and temperature. The experimental results obtained show that an initial 1725psi (11.9MPa) decrease in the net effective pressure caused 1.4% reduction in the volumes of residually trapped CO ₂, while another 1500psi (10.3MPa) reduction caused a further 3.2% drop in the residual saturation of CO ₂.