Discerning small time-lapse traveltime changes by isolating the seismic response of a reservoir using the Marchenko method

4D seismic studies aim to observe time-lapse changes in the subsurface between a baseline and a monitor study. These changes are generally small, and the seismic response from a deep reservoir can be concealed by reflections from shallow structures. Here, we introduce a novel way of isolating the reservoir response by means of the Marchenko method. First, this two-step approach removes the overburden interactions, and the second step eliminates the underburden reflections. Finally, the difference in traveltime is found by correlation of the (isolated) responses of the baseline and monitor study. An additional benefit of isolating the reservoir response is that internal multiples are more distinctly observed. These multiples have propagated through the reservoir more than once, therefore, their response experiences a larger traveltime perturbation, and provides further confirmation on the traveltime difference between the 4D studies.