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.
shore Brazil are found in Oligocene/Miocene sand-rich turbidites of contrasting architectural types. Reservoirs are sand lobes with thickness of 50 m, width of 1-5 km wide, and length of 2-10 km that display compensation stacking patterns. The reservoirs show bright reflections in a single amplitude trough corresponding to a relative decrease in impedance. In the study area, turbidite successions have high structural dips and complex spatial distribution. Their individual geometries are very difficult to map using conventional 3-D data.Detailed mapping of the geometry of Campos Basin turbidite reservoirs is required to guide the drilling of high-cost horizontal and multilateral wells needed for development of deepwater fields. An interpreter needs more than conventional 3-D structural and stratigraphic seismic visualization techniques for identification of compensation stacking patterns. Our group adapted some conventional stratal surface visualization techniques for better 3-D delineation of turbidite reservoirs in seismic volumes. This was important because a single frequency-independent horizon for attribute slicing could not be recognized. Adaptations were combined with enhancements to common volume visualization techniques by adding topological reconstruction methodologies for delineating sand bodies. These procedures became necessary because current visualization techniques are based only on physical values of seismic samples. Our study finds turbidite attribute strengths within stacking patterns that generally have subtle or nonvisible differences.The 3-D seismic visualization methodology in this article has an adaptive approach that can be summarized as:Adaptive windows of seismic traveltime data are transformed to horizon slices to map different depositional subsystems. Each depositional subsystem becomes topographically detectable from slices derived from 3-D seismic attribute volumes. Studies of Recent age analogs and geologic models guide this procedure. Such an approach better visualizes high-order stratigraphic sequences and can isolate thin, discontinuous reservoirs within channel/levee and lobe systems.Petrobras has studied outcrops and seafloor sonar images from Campos Basin to get a better description of the geometry and heterogeneities of subsurface turbidite reservoirs. In particular, Machado et al. (1998) studied Carapebus Formation, which contains the main turbidite reservoirs. This formation is still being deposited. Using side-scan sonar images and swath bathymetry from the seafloor, they identified low-sinuosity braided channels, pebbly mudstones (debris flows), and sand-rich turbidites in troughs and lobes. This showed that sedimentary processes such as channel avulsion control the geometry of turbidites in flat regions. Analysis of these modern depositional systems allows recognition of important types of reservoir heterogeneities, which can be also found in older turbidite systems.Importance of understanding turbidite architectural types and reservoir models. Oligocene/Miocene sand-ri...
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