Seismic interpretation of the Redwater Leduc Reef, Alberta

Taher M. Sodagar, Donald C. Lawton

Approximately 400 line-km of 2D seismic data were reprocessed and interpreted characterize the Redwater Reef in order to assess its potential for large-scale storage CO₂. The seismic data, of various vintages, were reprocessed to a common datum order to provide a uniform character for interpretation of the reef margin and characterize the internal geometry and facies of the reef. to of in to Interpretation of formation tops in the seismic data was constrained by synthetic seismograms generated from sonic and density logs available from two on-reef and four off-reef wells in the region. The synthetic seismograms tied reasonably well with the surface seismic data for the key formations. Generally, reflections dip gently towards the southwest direction in the 2D seismic datasets and there are no observable faults in the area encompassed by the Redwater Reef. Devonian age Upper Leduc and Mid-Leduc edges are identified clearly on the 2D seismic lines. Thickening of the reef rim and thinning inside and central of the reef are characteristics of the reef interpreted along individual lines and interpolated through isochron maps. The Cooking Lake and deeper seismic events show time-structure (velocity pull-up) beneath the reef due to higher velocity of the Leduc Formation carbonates compared with the off-reef Ireton shales. A restricted embayment (Duvernay Fm) was mapped from the seismic interpretation into the reef buildup in near the northwest flank and south-west boundaries. Depth-converted seismic event maps compensate for the velocity pull-up beneath the reef except where the shale embayments occurs, since only a single interval velocity for the reef was used in the depth conversion process. Some evidence of dolomitization in the Middle Leduc and Cooking Lake formations was interpreted in seismic lines along western side of the reef. Otherwise, internally to the reef buildup and away from the Duvernay embayments, the seismic character of the Leduc Formation is generally quite featureless.