DISCUSSION

It appears that the bright reflection disk centered on the injector well and the time delay beneath must indicate the extent of the steam zone, not merely hot fluid. The rock physics analysis has shown that the steam zone should be expected to show velocity decreases of up to 40%, whereas hot water or oil increases velocity by only 10% or less. Finite difference modeling of a reasonable steamflood velocity model shows strong diffractions and bright reflections emanating from the steam zone, that can be interpreted to match similar features in the field data. This analysis implies that the steam zone is about 40 m in diameter at the top of the P reservoir, 80 m in diameter at the base of the P reservoir, and heading to the north and west faster much faster than the south and east. This correlates with core measurements that the top part of the reservoir is at least one order of magnitude less permeable than the bottom part, and that for at least 13 months of steam injection, substantial heating had arrived at the T1 temperature monitor well to the west, but not the T2 well to the east.

My analysis suggests that the hot oil ring may be seismically transparent, but that the hot water ring might be visible since it causes about a 10% velocity increase. Close inspection of the time slices in Figures 37 to 41 shows a thin dark gray ring surrounding the white steam disk. This ring is about 15 m thick and corresponds to time pull-up (velocity increase) in the migrated profile sections. The dark gray amplitude suggests it is of opposite reflection polarity to the steam zone, which matches the predicted hot water properties. This dark gray ring may be the seismic view of the hot water steam condensate.

I have predicted that a large area of the 7-spot pattern would be subject to a fast-propagating cold high-pressure front. This pressure front should be seismically visible since it causes a 20% increase in velocity. Finite difference modeling shows that the high-pressure front can cause time pull-ups on seismic events due to velocity increase. The velocity models of Figures 30 to 34 show that the pressure front is propagating to the west, but not the east. Correlating the pull-up to features in the time slices of Figures 37 to 41 suggests that the pressure front propagates both north and west, but not south or east. Since the steam front is also observed to propagate to the northwest, but not the southeast, after 1 year of steam injection, it appears that mapping the early pressure front movement can be used to predict subsequent thermal and steam front fluid-flow propagation directions, many months in advance. This may be the most important result of my analysis of the Duri 4-D seismic monitoring data set.

 

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Figure 30 Reservoir velocity at 2 months

 

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Figure 31 Reservoir velocity at 5 months

 

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Figure 32 Reservoir velocity at 9 months

 

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Figure 33 Reservoir velocity at 13 months

 

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Figure 34 Reservoir velocity at 19 months

 

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Figure 35 3-D migrated inlines from the first three 3-D surveys. Baseline survey (left), first monitor after steam injection (center), and second monitor survey (right).

 

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Figure 36 3-D migrated inlines from the last three 3-D surveys. Third monitor survey after steam injection (left), fourth monitor (center), and fifth monitor survey (right).

 

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Figure 37 3-D migrated time slice at the base of the reservoir after 2 months of steam injection. T1 and T2 are the temperature observation well positions.

 

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Figure 38 3-D migrated time slice at the base of the reservoir after 5 months of steam injection. T1 and T2 are the temperature observation well positions.

 

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Figure 39 3-D migrated time slice at the base of the reservoir after 9 months of steam injection. T1 and T2 are the temperature observation well positions.

 

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Figure 40 3-D migrated time slice at the base of the reservoir after 13 months of steam injection. T1 and T2 are the temperature observation well positions.

 

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Figure 41 3-D migrated time slice at the base of the reservoir after 19 months of steam injection. T1 and T2 are the temperature observation well positions.

 

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Figure 42 Temperature observation well data to the west (T1) and east (T2) of the steam injector.