Shear wave technology has had a remarkably consistent presence in the Canadian exploration community for almost 40 years. Although publications from the earliest days are sparse, Unocal and CGG were conducting some of the earliest shear-wave experiments in Canada (Omnes, 1978). Since the initiation of the CREWES Project at the University of Calgary in 1988, P-S converted waves have been acquired, processed and interpreted by many exploration companies for more than 25 years, so there is a fair amount of experience in the application of P-S converted waves to land data in the Calgary geophysical community compared to elsewhere in the world. The quality of acquisition, processing and interpretation has steadily improved over that time and the number of geophysicists who are familiar with the use of shear waves in exploration has gradually increased. Nevertheless, it would be an exaggeration to say that multicomponent exploration is widely established in Canada. Some individuals within some companies use it to gain value in their exploration effort.
Several recent examples of adding value with converted waves have primarily been applications to heavy oil in NE Alberta. Mayer et al. (2014) have demonstrated that joint prestack PP-PS inversion produced the best estimates of Pimpedance, S-impedance and density, allowing for excellent reservoir characterization of the Athabasca oil sands reservoir. The zone of interest is the unconsolidated sands of the Lower Cretaceous McMurray Formation reservoir within which the bitumen oil sands reside. Limited angles of incidence are available in the data because of a large velocity increase at the Paleozoic immediately below the McMurray. As a result, density could not be directly estimated using AVO inversion, but it was successfully estimated from the joint PP-PS inversion. Neural network analysis that used the PP and PS PSTM volumes, attributes from the PP and PS AVO analysis and attributes from the PP-PS prestack inversion as inputs further improved the resolution of the results. Figure 1 shows the result of density inversion with neural network analysis. This density inversion indicates the existence of upper and lower sands, which is also indicated by the wells, however there is a transition from bitumen to water within the sands that is not indicated by density.
Toe-to-Heel-Air-Injection (THAI™) is an in-situ combustion process that is used for the recovery of bitumen and heavy oil. It combines a horizontal production well with a vertical air injection well placed at the toe. Compressional and shear velocities for heavy oil are extremely sensitive to temperature. As the oil is heated by the combustion process the velocity decreases causing distinct time-delay anomalies on timelapse (4D) seismic. These time-delay anomalies indicate that the combustion front is moving from the toes of the wells, where the air injectors are located, towards the heels. Downhole thermocouples are used to measure the temperature and hence provide control/calibration points.
Potash and Oil Sands are now the largest and most valuable resources in western Canada, particularly as conventional petroleum supplies are depleted. To a large degree, geophysical efforts towards the exploitation of these resources do not need to focus on exploration so much as resource delineation as necessary for mine development or enhanced extraction. Time lapse monitoring should also be an important aspect in oil sand recovery.