Plane-wave modeling

Figure 19 shows a finite difference acoustic simulation of a plane wave source leaving the surface at vertical incidence. The snapshot shows that the plane-wave is delayed by the steam zone in the center at the injection well, compared to the pre-steam synthetic. Diffractions are clearly visible at the center point. The outer limbs of the plane wave are pulled up in time, but the effect is too small to see in a static display.

Figure 20 shows the ``wave-stack'' Schultz and Claerbout (1978) that would have been recorded at the surface for the vertically incident plane-wave source. This wave-stack is similar to an NMO stack section, except it makes no velocity assumption. Note the presence of a strong diffraction associated with the steam zone. Also note the polarity changes and zero crossing along the top reservoir reflection from the steam zone to the high-pressure zone. The wave-stack clearly shows velocity time delay and amplitude focusing below the steam zone, and time pull-up at the survey edges beneath the portion of the reservoir containing the high-pressure front. All of these effects are somewhat visible in the field data sections of Figures 6 and 7.

 

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Figure 14 Velocity profiles of reservoir containing: viscous oil (left), steam (center), and high-pressure dissolved gas (right).

 

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Figure 15 Velocity model before steam injection. Heavy-oil reservoir is at 200 m depth.

 

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Figure 16 Velocity model after 5 months of steam injection. Low velocity anomaly in the center (dark gray) is due to steam, high velocity anomalies on the flanks (white) are due to the high-pressure front.

 

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Figure 17 FD acoustic modeling wavefield snapshots: before steam injection (left), during steam (right).

 

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Figure 18 FD acoustic modeled shot gathers: before steam injection (left), during steam (right).

 

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Figure 19 FD acoustic plane-wave snapshots: before steam injection (left), during steam (right).

 

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Figure 20 FD acoustic plane-wave wavestacks: before steam injection (left), during steam (right).