Time-lapse schedule

A total of seven 3-D seismic data sets have been acquired over the injector pattern of Figure 1. The timeline of the seismic surveys is shown in Table 1 with respect to the start of steam injection. Two baseline surveys were collected 3 days apart prior to steam injection in July 1992 for comparison with surveys taken during steam injection. The repeatability of the seismic measurements was confirmed with two baseline surveys to ensure that changes in repeated 3-D surveys were due to subsurface conditions, not acquisition-related variations. Continuous steam injection started in August 1992 and continues at the present time. Five 3-D seismic monitor surveys were acquired at intervals of 2, 5, 9, 13, and 19 months after the start of steam injection.