Methods and systems for monitoring a petroleum reservoir

Computational methods and systems for monitoring a petroleum reservoir are disclosed. A baseline survey is used to generate baseline data for a petroleum reservoir. Subsequent monitor surveys generate monitor data at different stages of production on the reservoir. The baseline data is reconstructed as if it was acquired at the locations of the sources and receivers of the monitor surveys, and the monitor data is reconstructed as if it was acquired at the same locations of the sources and receivers of the baseline survey. For each monitor survey, two four-dimensional ("4D") difference data sets are generated from the baseline and monitor data and from the reconstructed data. The 4D difference data sets are combined to reduce background and produce 4D signal data that provides reliable and accurate interpretation of production activity on the reservoir.