Perturbation theory has been used widely in many applications in seismology, more recently for time-lapse problems. Time-lapse is a cost-effective approach for monitoring the changes in the ﬂuid saturation and pressure over a period of time in a reservoir.The difference data during the change in a reservoir from the baseline survey to monitor survey are described through applying the perturbation theory. We deﬁned a form for the difference reﬂection data, ∆RPP (θ), in order of physical change or baseline interface contrast and time-lapse changes. A framework for linear and non linear time-lapse difference data is formulated using amplitude variation with offset (AVO) methods. The linear forms are equivalent to those of Landro (2001) and higher order terms represent corrections appropriate for large contrasts. We conclude that in many plausible time-lapse scenarios increase in accuracy associated with higher order corrections is non-negligible.
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