Geomechanical Response of the Tubåen Fm, a Compartmentalized CO2 Storage Reservoir, Snøhvit Norway
Chiaramonte, Laura; White, Joshua A.; Ringrose, Philip
The pressure build-up of large scale CO2 injection projects is one of the biggest challenges towards the development of a carbon sequestration technology. The pressure front creates stress gradients in the subsurface that can lead to dilation or slip along faults or fractures, hydro-fracturing of the caprock and potentially microseismicity. Furthermore potential compartmentalization of the storage reservoir can not only reduced the original estimated reservoir capacity, but exacerbates the pressure increase and associated hazards.
In this work we investigate the geomechanical response to the CO2 injection in the Tubåen Fm at the Snøhvit site focusing on the potential compartmentalization of the storage reservoir. This compartmentalization has been suspected due to the unexpected pressure rise during operations in the storage reservoir that has led to a considerable decrease in the estimated total capacity and to the abandonment injection operations.
The Snøhvit gas field is located offshore in the northern Norwegian Sea (Barents Sea). CO2 is separated from the produced gas and until 2011 it was stored underground in the Tubåen Fm. at approximately 2600 m depth. The Tubåen Fm. corresponds to a delta plain environment dominated by fluvial distributary channels and some marine-tidal influence. It is separated by the producing gas reservoir (Stø Fm.) by the Nordmela 1 and 2 Fms. that contain wide shale layers expected to act as flow barriers. The channelized nature of the Tubåen Fm. suggests the possibility of stratigraphic compartmentalization.
Structurally this area is extensively faulted, characterized by a dominant east-west-trending fault system, where the majority of the faults dip toward the basin axis and define typical horsts and graben geometry. However, it also present faults at high angles to this trend, leading to complex fault interactions and making fault compartmentalization a strong possibility as well.
Given the geometry of major faults and fractures in and above the reservoir, available estimates of the in situ stress tensor, and reservoir characteristics, we use a coupled hydromechanical approach to understand the geomechanical response of the system to the CO2 injection, focusing in particular on addressing the potential reservoir compartmentalization and its impacts on injection performance, CO2 distribution and migration outside of the storage interval.
AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013