Time-Lapse Crosswell Tomography In the Athabasca Tar Sands

Two crosswell seismic surveys were acquired in the Athabasca Tar Sands at Steepbank oil-sand reservoir before and after the start of the steam injection. The objectives of the survey were to monitor the shape and the movement of the steam zone and identify shale barriers effective enough to prevent steam from flooding the upper part of the reservoir. Since seismic velocities decrease with increase of temperature, any variations in compressional and shear wave velocities may indicate the advance of the steam zone. High resolution tomographic images have been derived from the crosswell data, using direct Pand shear wave arrival times. The direct shear wave arrival times have been identified using travel-time modelling. The initial velocity models have been reconstructed using horizontal rays between two wells and sonic log data.