Figure shows an enlarged version of the reservoir zone, before the onset of waterflooding. The top of the reservoir is at 2 km depth, and the reservoir is 50 m thick. Figure shows the same enlargement, but after one time step of water injection. The two water injection wells are clearly located at 2 km and 3 km distance, at the centers of the water diffusion fronts. The water invaded zones (blue/grey) represent an increase in P impedance in the reservoir, with respect to the initial pre-flood reservoir conditions. Figure shows the S impedance values in the reservoir after one time step of water injection. The (red/grey) water invaded zones represent a decrease in S impedance in the reservoir, with respect to the initial pre-flood conditions. Since the magnitude of shear impedance change is nearly twice as large (although opposite polarity) as the P impedance change in the water invaded zone (Table 1), the water injection shear impedance plume extends a larger distance away from the wells. This implies that shear waves may be more sensitive to monitoring water injection processes in light oil sand reservoirs than P waves.
Figure shows the reservoir P impedance map after two time steps of waterflood. Now the P impedance diffusion front has extended about 300 m away from each injector. The (blue/grey) water invasion zone indicates a substantial increase in P impedance within the waterflood as compared to the initial reservoir conditions with 100% oil saturation in place. Figure shows the S impedance map after two time steps of waterflood. Again, the S impedance front has extended about 300 m away from each injector, and its (red/grey) color indicates a decrease in shear impedance within the reservoir, at about twice the magnitude of the P impedance change, compared to the initial reservoir conditions.