The aim of this paper is to investigate the effects of CO2 sequestration on groundwater abstraction above the storage formation. Large-scale (10Mt/yr) CO2 injection in underlying saline aquifers is considered using a fully compositional simulator to study the pressure distribution, CO2 leakage and inter-layer brine flow. Structural, residual and solubility CO2 trapping are taken into account while the model domain is considered to have no-flow boundaries to simulate CO2 injection under the context of either pressure not being able to be dissipate quickly (due to other CO2 injection processes, for instance) or the formation being self-contained. Changes in salinity are affected by groundwater abstraction and although not caused by injection itself, can be magnified by such processes. We also conclude that the time at which CO2 leakage, pressure perturbations and upward brine flow are at their peak in overlying aquifers (layers above the injection site) may be significantly after injection has ceased (50-150 years in some cases) and could potentially cause groundwater movements, land surface uplift or rock fracturing long after the injection phase has ended.