A study on the impact of storage boundary and caprock morphology on carbon sequestration in saline aquifers

Structural trapping is known to be the primary storage mechanism in geological carbon sequestration (GCS), where the injected CO2 rises upwards due to buoyancy forces and becomes trapped under an ultra-low permeability layer. Although it is relatively common in GCS studies to assume a planar caprock for the synthesised models, in a real scenario this is not always the case as the caprock might exhibit some small- or large-scale topography changes. Moreover, little is known about the impact of the caprock morphology on the CO2 plume migration and the storage capacity. In this work, we performed a preliminary study of the effects of boundary conditions on the CO2 plume migration and dissolution. This was performed because most of the case study models which are employed for GCS studies are part of larger reservoirs. The obtained results were used in the simulation models of the second part of the work, to model an infinite-acting reservoir appropriately. Three different volume modifier values of 10(5), 10(7) and 10(9) were considered on either one side or both sides of the reservoir for both horizontal and tilted caprock models. The CO2 dissolution in the tilted models was seen to be higher once the multiplier was on the opposite side of the slope. Horizontal models closed on one side (closed faults, salt walls, etc.) were also found to exhibit more significant dissolution than models which were open from both sides. We subsequently investigated the impact of caprock morphology on the CO2 plume advancement and its structural and dissolution trapping mechanisms by performing numerical simulations on nine synthetic models. The dissolution and migration distance are seen to be at a maximum for tilted reservoirs, where the CO2 has more space to migrate upwards and to interact with more formation water. The lowest dissolution occurred where the significant portion of the injected CO2 was trapped in a sand ridge or an anticline. Moreover, the possibility and also the amount of structural trapping was evaluated using an analytical method, and the results showed a fair match with the ones from the numerical simulation. We believe that this methodology could be applied for site screening prior to performing numerical simulations. (c) 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.