The Effect of Aquifer/Caprock Interface on Geological Storage of CO2

Abstract

Abstract The migration of CO 2 stored in deep saline aquifers depends on the morphology of the top of the aquifer. Topographical highs, such as anticlines, may trap CO 2 and limit the distance migrated, or elevated ridges may provide pathways enabling CO 2 to migrate further from the injector. For example, seismic data of the Utsira formation at the Sleipner storage site indicates that a branch of the CO 2 plume is moving to the north [1] . It is therefore important to study the interface between the aquifer and the caprock when assessing risk as CO 2 storage sites. Undulations in the top surface of an aquifer may either be caused by sedimentary structures [2] , or by folding. In addition, irregularities may be generated by faulting [2] . Large-scale features are detected using seismic data (i.e. structures with amplitudes greater than 10 m), and such structures will generally be included in reservoir or aquifer models. However, smaller- scale features could also have an effect on a CO 2 plume migration, and this is the topic of our study. We have conducted simulations in models with a range of top-surface morphology, and have examined the distance migrated and the amount of dissolution. The results from this study suggest that the effects of sub-seismic variations in the topography of the aquifer/caprock interface are unlikely to have a significant impact on the migration and dissolution of CO 2 in a saline aquifer, compared with tilt or permeability anisotropy. The results were most sensitive to the kv/kh ratio during the injection period.