Imaging and characterizing time-lapse changes in reservoir properties rely on accurate estimation of the corresponding time shifts and amplitude changes. We evaluated the accuracy of competing time-shift extraction algorithms — cross correlation, nonlinear inversion, dynamic warping, the correlated-leakage method, and the optical-flow-warping method — for estimating 4D time shifts, particularly from subsalt reservoirs. A synthetic model of a Gulf of Mexico field was used for testing these methods. The model contains both subsalt and extra-salt reservoirs. We imposed 4D velocity changes within both reservoirs and in the overburden of the subsalt reservoir. Each of the time-shift extraction methods was evaluated, and each was found to have various strengths and weaknesses. The correlated-leakage and optical-flow-warping methods reproduced the model time shifts most accurately and with the best resolution.

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