Two experimental time-lapse converted-wave surveys were acquired by Imperial Oil Resources Ltd. at Cold Lake, Alberta, where bitumen is produced from the Clearwater Formation by means of cyclical steam stimulation of the reservoir. The survey consisted of seven source lines and one common receiver line. The P-P and P-S data from three common CDP/CCP lines were processed fully for each survey. The P-S data processing flow included post-NMO spiking deconvolution, f-k filtering and spectral balancing to enhance the important reflections and boost the higher frequencies. Each pair of P-P and P-S lines was interpreted on a workstation and Vp/Vs ratios were calculated from the Grand Rapids to Devonian interval transit times. Values of Vp/Vs over the steamed zone ranged from 2.01 to 2.20 and over the cold reservoir averaged 2.20, which is in agreement with the theoretical values. In general, there is a good correlation between low Vp/Vs ratios (below 2.1) and the locations of steam injection wells.
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