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Abstract: 3-D Seismic Stratigraphic Inversion: a Lithology-Based Approach for Seismic Reservoir Characterization in Deep Water Campos Basin

Abreu, C. E B. S.; P. R. S. Johann; L. C. S. Freitas; C. H. L. Bruhn; R. Beer; D.J Sarzenski; Z. Camoleze - Petrobras/E&P

Most barriers to vertical fluid flow are easily recognized in well logs, such as gamma-ray and neutron-porosity logs. Reservoir heterogeneities (e.g. interbedded mudstones and calcite-cemented horizons) in turbidites from deep water Campos Basin usually show subtle responses in conventional seismic amplitude data (Fig. 1); this may be due to their reduced thickness and/or the low acoustic impedance contrast between the non-reservoir layers and the reservoir sandstone. Nevertheless, the mapping of these heterogeneities is very important for defining the reservoir drainage strategy, particularly the positioning and completion of horizontal and deviated wells. Nowadays, a great effort is being undertaken to overcome these obstacles.

The use of 3-D seismic stratigraphic post-stack inversion is proposed to improve reservoir characterization, by using both inverted acoustic impedance and reflectivity images. This technique involves the use of three main types of data: (1) a conceptual, regional stratigraphic model, (2) a well-log derived acoustic impedance model, and (3) a stacked and migrated 3-D seismic volume. The expected results include a better description of the reservoir internal and external geometry, the assessment of reservoir properties in non-drilled areas, and a seismic processing quality control tool, by investigating the final residual volume from the inversion procedure. A great advantage of this methodology is the integration of seismic information and well-log data at the oil-field scale.

The study area, a giant oil field from deep water Campos Basin, includes 26 wells with sonic and density logs, which provided a reliable spatial variant a priori information, the geostatistically-based acoustic impedance model generated from well-log data. The seismic-derived volumes, constrained by well information and conceptual stratigraphic models, enabled a more accurate mapping of the reservoir boundaries (Fig. 2) and the prediction of the reservoir properties (particularly in the inter-well area).

The 3-D seismic stratigraphic inversion procedure consists of five main steps: (1) volumetrically constrained well-seismic calibration, (2) stratigraphic deconvolution, (3) 3-D acoustic impedance modeling, considering the well and stratigraphic information, (4) seismic stratigraphic inversion, (5) interpretation of the high- resolution, inverted seismic volumes. The uncertainties associated to well-log acoustic impedance and seismic data values are also taken into account, controlling the freedom degree in which the final solution is obtained.

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