At 2 months, the steam zone is already visible, and shows up as a 10-15% decrease in velocity, and bright diffractions and reflections at the injector location (Figures 30 and 35). Because the velocity decrease is not maximal compared to core measurement predictions for steamed rock, steam saturation may only be about 25% on average vertically. The width of the steam zone appears to be about 50 m, and is fairly radial as shown in Figure 37. A steam leak is apparently visible from the time delays in the overburden at about 75 ms pseudodepth.
To the north and west of the injector, a transient pressure front propagates away from the injection well. It is marked by a 20% increase in P-wave velocity, which matches predictions made by the steamflood model and the Duri core data. To the immediate west of the injector, a small increase of 10% in P-wave velocity may correlate with a ring of hot water (condensed steam), which is seen to form an annulus in the time slice of Figure 37. Beyond that, to the east, relatively little change in velocity has occurred. However, a polarity reversal is developing along the base of the P formation reflector, which may indicate that gas saturation increases are changing the seismic impedance within the reservoir, with little effect on the velocity; or that heating in the K formation below the main reservoir is changing the impedance contrast at the P/K boundary. These results suggest that heat from the injector has not arrived at either of the temperature observation wells at this time, which correlates with the well data of Figure 42.