At 19 months, the steam zone has expanded even further outward towards the northwest as seen in the time slice of Figure 41. More heat has been transferred into the reservoir, as seen by the pronounced velocity decreases to the east and west of the injector in Figure 34. The pressure front has propagated almost completely out of the survey area, and is trailed by a strong thermal front toward the west. For the first time, a substantial velocity decrease is observed to the east in Figure 34. The suggestion from the seismic data that heat has now propagated in both the east and west directions is supported by the temperature logs of Figure 42, in which the first heating at the eastern observation well T2 has been recorded.
The steam disk has a full -40% change in velocity, which suggests that the entire reservoir volume is saturated with steam in a 100 m diameter disk centered on the injector. The temperature log for the T1 well on the west shows temperatures of over 300 F, which implies that the steam front has propagated a full 100 m from the injector to the west. The time slice of Figure 41 seems to show the edge of the steam front has just arrived at the T1 well, which is in nice agreement with the well data. Extrapolating this seismic and well tie, the time slice suggests that steam has propagated perhaps as far as 150 m or more to the northwest of the injector.