Traveltime changes

Figure 28 shows the traveltime changes along the base of the reservoir, obtained by subtracting each traveltime curve from the baseline traveltime curve. In the center at the steam injector, traveltime delays occur. The first three monitor surveys show traveltime delays of about 10 ms, and the fourth and fifth monitors show increasing traveltime delay at about 15 and 20 ms respectively. This indicates that the steam zone is expanding and heating adjacent rock. To the west of the injector, traveltime pull-ups of about 10-15 ms occur during the first three monitors. This is consistent with a pressure front propagating to the west. At monitor surveys 4 and 5, the traveltime change decreases somewhat, probably due to a thermal front moving out radially and decreasing the velocity. To the east the traveltime changes are small, indicating that not much fluid flow is occurring in that direction.