The concept of time-lapse (or 4-D) seismic monitoring is straightforward: A baseline 3-D survey describing initial reservoir conditions and a subsequent monitor survey (or surveys) recorded after conditions have changed are calibrated, compared, and the intersurvey differences analyzed and interpreted in terms of net variations in pore fluid saturation, pressure, or temperature inside a hydrocarbon reservoir.

Seismic monitoring thus depends largely upon whether “repeatability” of surveys is achievable. Ideally, the difference between surveys should contain nothing but the changes in reservoir properties. However, it is almost impossible to obtain perfectly repeatable (or identical) time-lapse seismic surveys in the real world....

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