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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
4-D Multi-component Seismic Modeling of CO2 Fluid Substitution in the Redwater Devonian Reef, Alberta, Canada
(1) Geoscience, University of Calgary, Calgary, AB, Canada.
The Devonian Redwater reef in Alberta, Canada, is being evaluated for geological storage of CO2 for the Heartland Area Redwater CO2 Storage Project. It is located close to large sources of CO2 in the Redwater-Fort Saskatchewan-Edmonton region. The Leduc reef at Redwater is one of the largest Devonian reefs in the Western Canada sedimentary basin and is the third largest oil reservoir in Canada. The main objective of the study was to build a 3D geological model of the reef, from the reef interior to off-reef, and examine the seismic response of the reef to CO2 saturation in the Leduc Formation. Fluid replacement and 3D seismic modeling were undertaken to generate PP and PS synthetic seismic data to study the consequences of CO2 saturation on the seismic response of various reef facies and formations below the reef, based on seismic attributes.
Common shot multi-component 3D ray tracing modeling was undertaken to evaluate variations in the seismic response of the Redwater reef margin for CO2 saturation in the Upper Leduc interval. The input geological model was based on well data and depth-converted seismic data from approximately 400 line-km of 2D seismic data were previously reprocessed and interpreted in the area. P-wave and P-S wave ray tracing synthetic seismic reflections demonstrate similar seismic attributes for the Mannville, Nisku, Ireton, Cooking Lake, and Beaverhill Lake Formations, but with lower dominant frequency in PS data. Seismic sections and time structure maps display positive structure below the reef for both PP and PS, due to the lateral velocity change from on-reef to off-reef, but are compensated in the depth maps.
Terminations and the lateral position of the Upper Leduc and Middle Leduc events are obvious on the pre-stack time-migrated sections and improved on the depth-migrated section on PP data while it is less evident in PS data. Higher amplitudes at the base of Upper-Leduc member are evident near the reef margin due to the higher porosity of the foreslope facies in the reef rim compared to the tidal flat lagoonal facies within the center of the reef for both PP and PS data. 4D seismic modeling predicts a sensible amplitude change and travel-time difference (4ms) for the seismic data before and after CO2 saturation. High amplitude reflections occurring at the top of upper-Leduc, top of the rim, and base of upper-Leduc near the reef edge provide good markers to observe and monitor CO2 saturation with 3D seismic data.