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fax 01-972-952-9435. AbstractAfter producing 400 million barrels of oil along the last five years, Marlim Sul field, situated in Campos Basin, Brazil, applied its first time-lapse seismic acquisition. The oil is being produced from six different reservoirs, each one with different characteristics. The main common point of them is the water drive mechanisms, and therefore the flow path of the injection water is the prime purpose of this 4D action. Almost all producers have seen the breakthrough of water, sometimes after the forecasted time, sometimes before. The seismic data were acquired by a streamer steering system and received special attention in terms of velocity analysis and crossequalization process. The preliminary analysis indicates some interesting conclusions. The water path seems to be less regular than expected from flow simulation and indicates a trend in rock permeability. This knowledge allows a better match of the model, and a better control of production and injection rates. In addition, some areas are less flooded than expected, wich permits the proposal of new infill drillings, in order to recover this additional oil, depending on the economic analysis, as well as a new infill well, proposed before the acquisition, is not in the better position, and may be relocated or cancelled. Furthermore, the communication of two blocks, situated one above the other, was strongly suggested by the presence of an anomaly related to increase of gas saturation in the higher block derived from the depletion of the lower one. These simple conclusions reveal the power of time-lapse seismic acquisition, and evidence the importance of a permanent reservoir monitoring for the optimization of recovery factor and the profitability of the exploitation project.

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