  The data-driven Marchenko method is able to redatum wavefields to arbitrary
locations in the subsurface, and can, therefore, be used to isolate zones of
specific interest. This creates a new reflection response of the target zone
without interference from over- or underburden reflectors. Consequently, the
method is well suited to obtain a clear response of a subsurface reservoir,
which can be advantageous in time-lapse studies. The clean isolated responses
of a baseline and monitor survey can be more effectively compared, hence the
retrieval of time-lapse characteristics is improved. This research aims to
apply Marchenko-based isolation to a time-lapse marine dataset of the Troll
field in Norway in order to acquire an unobstructed image of the primary
reflections, and retrieve small time-lapse traveltime difference in the
reservoir. It is found that the method not only isolates the primary
reflections but can also recover internal multiples outside the recording time.
Both the primaries and the multiples can then be utilised to find time-lapse
traveltime differences. More accurate ways of time-lapse monitoring will allow
for a better understanding of dynamic processes in the subsurface, such as
observing saturation and pressure changes in a reservoir or monitoring
underground storage of hydrogen and CO2.
