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During geological storage of carbon dioxide in deep saline aquifers part of the stored carbon dioxide dissolves inthe brine. This dissolution trapping is one of the key trapping mechanisms of CO2 and its understanding importantwhen making estimates of the performance of the storage. Dissolution occurs in the carbon dioxide and brineinterfaces, i.e. into brine in contact with the edges of the free phase carbon dioxide plume and into residual brineleft inside the plume after the push stage.In this modeling study the scale effect of dissolution trapping for CO2 in a deep saline aquifer and the use ofa push-pull CO2 injection-withdrawal test in quantifying field scale dissolution trapping, and in particular therelevant spatial and temporal scales of this process, is investigated. A push-pull test consists of two stages. First,a push stage during which supercritical carbon dioxide is injected into the formation; then, a pull stage duringwhich formation fluid is withdrawn. The second stage needs not be initiated immediately after the first, a waitingperiod of varying duration may be applied. Different withdrawal fluid compositions are obtained depending on theresting period between the injection and the withdrawal stages. The different waiting times between injection andwithdrawal of CO2 permits buoyancy to act for different periods and alter the carbon dioxide plume shape. Thedifferent plume shape can in turn give rise to different carbon dioxide-brine interfacial areas, where mixing anddissolution occurs.In comparing scenarios with different waiting time between injection and withdrawal this effect of mixing wasstudied. The injection-withdrawal was simulated into a sandstone target layer located at a depth of 1600 m, withproperties similar to the Heletz formation where an injection experiment is planned. Simulations of the push-pulltest were carried out with the TOUGH2/ECO2N simulator. The preliminary results indicate that a test sequencewith multiple push-pull stages in a series could be useful tool for analysis of the dissolution trapping.