Hunting CO2 leakage systems
Ingrid Anell, SUCCESS PostDoc, UNIS.
Utah’s southwest landscape is dominated by wide-spread successions of sedimentary rock, a veritable utopia of cliff and canyon exposures for the eager sedimentologist. It is colorful landscape with unique exposures of strata ranging from the Cambrian to the Tertiary. The region is situated atop the Colorado Plateau, a flat-lying largely un-deformed uplifted area, surrounded by complex folded and faulted mountain chains. The 1000-1500 m of epeirogenic uplift of the plateau occurred some 5 Myr ago and rivers immediately began to cut down intensely into the sediments creating the present cliff faces, revealing millions of years of deposits. Prior to this Utah was a flat landscape hovering just above or just below sea-level.
Fig. 1 The first part of our Utah expedition was focused on field-work for a Master Project on detailed analysis of fault cores, a project which will contribute to a global database on fault core architecture, linked to the Imperva project of CIPR, UiB and UNIS. Here a fault exposure from the Permian Cutler Group, near Arches National Park
Fig. 2 Prograding clinoforms in the Cretaceous Ferron Sandsstone Member within the San Rafael Swell
An important part of furthering our understanding of the Longyearbyen CO2 reservoir is linking the large porous Triassic prograding clinoforms in the northwest Barents Sea to the more unconventional onshore Triassic reservoir deposits. Our aim is to recognize how to link seismic scale observations to field-observations and better grasp the three dimensional characteristics and development of prograding clinoforms. In Utah we had the chance to observe both large-scale prograding successions on km-scale as well small-scale down-lapping features (Fig. 2). The incised cliffs provided excellent 3D exposures of the prograding systems.
Fig. 3 Bleached fractures at Humbug flats in rocks of mid-Jurassic age
In the Humbug Flats the fieldwork was focused on fault-tip processes. Here, the hanging wall of a larger fault hosts a series of smaller faults and multiple fractures and deformation bands. Within the Jurassic Entrada Formation, in mainly red-colored units, many fractures near the faults, and spreading from the fault-tips (were the throw reaches zero), have been bleached pale yellow by CO2-CH4 bearing fluid (Fig. 3). The bleaching varies from a few mm to several cm, and sometimes whole sections up to meter-scale. The leakage and spread of CO2 in Utah is a natural laboratory for studying the behavior of CO2 to better analyze future sequestration repositories. The analysis of these fractures is part of an ongoing research project of the Longyearbyen CO2 Lab (Ogata et al., 2012).
Fig. 4 The Utah landscape at Humbug Flats, showing the bleached pale yellow sandstone reservoir
References: Ogata, K., Senger, K., Braathen, A., Tveranger, J. and Olaussen, S. (in press) - The importance of natural fractures in a tight reservoir for potential CO2 storage: case study of the upper Triassic to middle Jurassic Kapp Toscana Group (Spitsbergen, Arctic Norway) - Advances in the Study of Fractured Reservoirs, Geological Society of London Special Publication.