Summary Seismic characterization of the Devonian Nisku Formation in the Wabamun area, Alberta, Canada has revealed two primary groups of anomalies. The first group is interpreted to be footprints of geological discontinuities which are induced by dissolution and karsting in a geologic formation shallower in the stratigraphy. Even though there is no evidence to indicate that the integrity of the Nisku Formation or the overlying caprock has been compromised, such geologic discontinuities should be taken into consideration if supercritical CO2 were to be injected into the Nisku Formation. The second group is interpreted to be due to contrasts in lithology and/or porosity of the Nisku Formation. This interpretation is supported by constraints provided by well control and by seismic modeling. Finally, our analysis has identified favorable low-impedance, potentially high-porosity, locations that could be developed for a CO2 injection site.
Introduction The province of Alberta contributes more than 30% to the total Canadian CO2 emissions, according to recent statistics by United Nations Framework Convention on Climate Change (2007). In an effort to offset the carbon emissions, several CO2 sequestration projects were launched recently in the province. These include the Alberta Saline Aquifer CO2 Project (ASAP), the Heartland Area CO2 Sequestration Project (HARP), and the Wabamun Area CO2 Project (WASP). In the Wabamun area, the Nisku Formation has been advocated as a sink for large-scale CO2 sequestration project (Michael et al., 2008) with injectivity in the order of 1 Mt/year. Seismic characterization was undertaken as part of the first phase of the project, with primary objectives to generate detailed attribute maps of the Nisku Formation and delineate any potential geologic discontinuities in the area that may compromise the integrity of the CO2 storage within this formation. This abstract presents some of the results of the study.
Study Area The proposed CO2 sequestration area is located in the central plains of Alberta, approximately 50 km southwest of the capital Edmonton. The injection target is the Devonian brine-bearing Nisku Formation. The Nisku aquifer sits on the edge of a carbonate shelf and consists predominantly of dolomite minerals. The aquifer ranges in thickness from 40 to 80 m and occurs at a depth between 1800 - 2000 m and its properties, such as temperature and salinity, make it a favorable candidate for CO2 storage (Michael et al., 2008). Furthermore, the overlying Calmar shale makes a good cap rock, which prevents supercritical CO2 from migrating upwards into shallow aquifers. The seismic characterization is focused on a local area, where favorable conditions in terms of seismic coverage and other factors exist.
Approach and Results The seismic characterization is based on analyzing and interpreting a poststack seismic dataset consisting of more than two hundred 2D lines and seven 3D volumes distributed over an area of approximately 20,000 km2. This enormous dataset was available from various exploration programs in the area, and therefore has different acquisition and processing vintages. Thus, prior to interpretation, two primary steps were necessary: data calibration and amplitude normalization.