Multiple 3-D seismic surveys have been acquired at time-lapse intervals over a heavy oil reservoir in the Duri field, Indonesia, to monitor the progress of an active steamflood. Time-lapse 3-D seismic images show dramatic and complex changes in the reservoir zone over a wide area, compared to baseline seismic data recorded prior to steam injection. Careful consideration of steamflood fluid-flow, rock physics measurements, finite-difference seismogram modeling, 3-D seismic imaging and velocity analysis leads to an integrated interpretation of the 4-D data set.
Anticipated large decreases in seismic P-wave velocity Vp near the injection well correlate with the presence of a hot steam-saturated zone. Unanticipated large increases in Vp and reflectivity changes in an annulus around the steam zone are consistent with a high-pressure front, in which initial free gas in pore space is raised above the bubble point pressure and dissolves into liquid oil. Horizontal and vertical anisotropy in flow directions inferred from these seismic observations correlate with two temperature monitor wells, and in situ measurements of upper and lower reservoir permeability. Since the pressure front propagates out from the injector at least one order of magnitude faster than either the thermal or steam fronts, monitoring it may be useful for predicting future flowpaths of heated oil and steam, months in advance.