A 3D permanent reservoir monitoring system has been installed for Shell, on a heavy-oil onshore field situated in the north-east region of the Netherlands, in the context of re-development of oil production by Gravity-Assisted Steam Flooding. We have continuously monitored the spatial expansion of the steam chest injected in the reservoir over more than a year. The sources and receivers are buried below the weathering layer to reach the seismic repeatability required for measurement of weak 4D signal. Efforts are made to attenuate source and receiver ghost that has been identified as the main cause of residual 4D noise in land permanent monitoring. A 3D migration has been applied to the data to focalize the diffracted 4D signal. The very high sensitivity of our buried system coupled with appropriate de-ghosting and migration allows us to track very small variations of the reservoir physical properties in both the spatial and calendar domains. A “daily 4D-movie” of the reservoir property allow us to propose a scenario which explains the unexpected behavior of the production and confirms that the steam does not follow the expected path to the producer wells but rather a more complicated 3D path within the reservoir.


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