--> Abstract: Characterization of the 3-D Architecture of Deep-Water Reservoirs From Outcrop Analogues in the French Alps and Application to the Namorado Field (Offshore Brazil), by P. Joseph, O. G. de Souza, Jr., R. Eschard, D. Granjeon, O. Lerat, and C. Ravenne; #90933 (1998).

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Abstract: Characterization of the 3-D Architecture of Deep-Water Reservoirs From Outcrop Analogues in the French Alps and Application to the Namorado Field (Offshore Brazil)

Joseph, P. - IFP; O. G. de Souza Jr. - Petrobras/E&P; R. Eschard, D. Granjeon, O. Lerat, C. Ravenne - IFP

The Eocene Annot Sandstone in the French Alps corresponds to a turbiditic system up to 1000 m thick, which has filled large morphologic gutters induced by tectonic activity. Detailed field studies have recently been undertaken on well-exposed 3D outcrops at a reservoir scale (kilometric), in order to analyze and reconstruct the architecture of deep-marine gravity deposits. This reconstruction is based on the measurement of vertical sedimentological sections, the mapping of sand units, the calibration and interpretation of continuous photo-mosaics of the outcrops. Then 3D grid blocks of the geometry and facies distribution of the reservoir units are built using geomodeling and geostatistical tools, and seismic modeling is performed in order to analyze the seismic response.

Some of these sites have been used to provide guidelines for the 3D reservoir modeling of the Namorado field (Upper Albian - Cenomanian), which is one of the most important producing oil fields on the Brazilian shelf (Campos basin). The turbidite reservoirs are trapped in a narrow and sinuous depression (a few kilometers wide), controlled by the movement of the underlying Aptian evaporites. The Namorado reservoir sandstones are organized in three major sequences (U1, U2 and U3), between 20 to 110 m thick, which are each subdivided in three packages (Fig. 1):

- a sandy unit, with a kilometric extension and up to 30 m thick, beginning frequently by an erosion surface and composed of coarse-grained channelized and amalgamated pebbly sandstones, sometimes graded, resulting from high-density turbiditic flows. Minor amounts of thin Bouma turbidites and hemipelagic mudstones correspond to overbank and inter-channel deposits.

- a mixed unit, composed of alternating shaly and sandy beds, organized in Bouma low-density turbidites, associated with carbonate debris-flows and slumps. This unit is interpreted as a channel-levee system, a few meters deep (thinning-upward sequences and lateral evolution to hemipelagic mudstones).

- a shaly unit composed of hemipelagic shales and bioturbated marls, which corresponds to a break in the sand supply and has been interpreted as the equivalent of a maximum flooding surface.

This organization is very similar to the sequences identified in the Cîme Dieu de Delfy site, in the Sanguinière area (Fig. 2):

- the amalgamated channelized sand unit corresponds to a prograding system during the base level fall. Periodic pauses in the sand supply induced some shale breaks (partly eroded by the subsequent sand deposits), which act as permeability barriers inside the sand package: their size and frequency may be quantified using photo-mosaics calibrated with sedimentological sections.

- channel-levee systems are organized in genetic sequences related to the development of overbank deposits during channel activity, followed by the filling and abandonment of the channel. These sequences constitute compensation cycles in which individual beds pinch out rapidly: their length and thickness may be quantified in order to derive geostatistical parameters for the reservoir stochastic modeling (lithofacies proportions, correlation lengths).

- small Bouma turbidites dominated by parallel laminations and shaly interbeds appear as continuous layers at the outcrop scale and confirm the interpretation in terms of major abandonment surfaces (MFS).

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil