Ane Lothe

Reservoir geology of the Utsira Formation at the first industrial-scale underground CO2 storage site (Sleipner area, North Sea)

Abstract At the Sleipner fields in the North Sea, CO2 is being injected into sands of the Miocene-Pliocene Utsira Formation, which is overlain by thick Pliocene shales. The highly porous (35%–40%) and extremely permeable (approximately 2 D) Utsira sands are organized into approximately 30 m thick packages. These packages are separated by thin (predominantly 1 m thick), low-permeability shale layers, which are assumed to contain potential fluid pathways of erosive or deformational origin. A 6.5 m thick shale layer close to the top of the sands separates an eastward thickening sand wedge from the main sand package below. Migration simulations indicate that the migration pattern of CO2 below the shale layer would differ strongly from that within the sand wedge above. Time-lapse seismic data acquired prior to the start, and after three years, of injection confirmed a reservoir model based on these findings and showed that the thin shale layers act as temporary barriers and that the 6.5 m thick shale layer does not fully inhibit upward migration of CO2.

Reservoir geology of the Utsira Sand in the southern Viking Graben area - a site for potential CO2 storage.

Since October 1996 Statoil has started to inject CO2 coming kom the Sleipner Vest Fieldin the southem Viking Graben area into a saline aquifer at a depth of approximately 900 m. This is the first case of industrial scale CO2 storage in the world (1 million tons per year). Careful monitoring of the behavior of the storage facility is hence required. To this end different time-lapse seismic surveys have been planned (presented in a companion paper: Brevik et al., this volume). In this paper the interpretation of the base survey acquired before injection is presented. The most likely pathways for CO2 migration in the vicinity of the injection point have been indicated

CO2 Storage Capacity Estimates for a Norwegian and a Swedish Aquifer Using Different Approaches – From Theoretical Volumes, Basin Modelling to Reservoir Models

Open dipping aquifers might offer a unique possibility to store huge quantities of carbon dioxide. Many different modelling approaches have been used to quantify possible storage capacities often giving very diverse results. In this study, we applied three different methods to calculate and model theoretical volumes, structural trapping volumes using a basin modelling tool and capacities obtained from dynamic reservoir simulations. We tested end-member scenarios for different critical parameters. The results for two stratigraphic confined open/semi-closed dipping saline aquifers, the Garn Formation (Norwegian Sea, Norway) and the Faludden sandstone (Baltic Sea, Sweden) show broad variations. For the Garn Formation CO2 storage capacities vary from 2.0 to 8.4 Gt. Taking into accounts all results, we estimated a representative storage capacity ranging between 2.0 and 3.5 Gt. In the case of the Faludden sandstone the different modelled scenarios give a spread from 10 to 836 Mt and a representative capacity of 250–435 Mt was defined. We will show and discuss how the different estimates are calculated, how they are related to each other and finally exclude unreliable results. Furthermore we compare our results with published data from the same areas. This will demonstrate the complexity and difficulty of a direct comparison of geological CO2 storage estimates and pinpoint to the need for a general strategy to compare modelling results for geological CO2 storage estimates.