Abstract: New 3D Visualization and Analysis Tools Improve Prospect Evaluation in a Deep Offshore Environment

Marini, Iunio; Maurizio Cardamone; Luca Bertelli - ENI/Agip

The emerging trend of seismic data interpretation, moved quickly during the past few years towards a huge increase of the project database magnitude. Larger and larger areas need nowadays to be analyzed through the usage of conspicuous multi-volume 3D attributes, while a severe exploration-to-production cycle time reduction has become a hard constraint for seismic interpreters. Upon this scenario, not only data integration, but also a robust methodological path is required. This implies the need of developing a direct geological approach on large multi-attribute 3D datasets. The final expectation is to implement a real time problem solving capability concerning generation of a geological and sedimentological model; definition of interesting targets (objects, leads); detailed prospect assessment and well proposal.

The case history here presented concerns the study of an exploration license located in the Nigeria deep offshore. The study was carried out over 1700 sq. km. acreage of a multi-volume 3D seismic dataset (migrated stack, continuity, AVO attributes, acoustic impedance). The area is located just beyond the Niger Delta Province. Its geological history is a part of the West African margin evolution. The sequence of interest ranges from the Late(?) Miocene to the Plio-Pleistocene with a physiographic setting varying around the slope to basin transition.

Methodology. An innovative methodology was implemented here as required by the specific needs (massive use and effective integration of different 3D seismic attributes over a 1700 sq. km. area, tight project schedule) and by the requested goals (develop a geological and sedimentological framework for the sequences of interest, suggest new plays and prospective areas, define and map all the possible targets). The adopted work flow took full advantage of the 3D visualization methodology that enabled a volume based interpretation opposite to a routinary horizon based approach. This allowed us to develop and validate quickly and effectively large to medium scale sedimentological models, even dealing with the largest 3D data volumes.

Geologic and Sedimentologic Model. For each of the major sequences, direct visualization analysis were carried out focusing on their internal structure. This was effectively achieved using the peculiar features of the voxel visualization software: slice animation, opacity control, interactive view point setting, illumination, connectivity. The original drainage system of this "slope to basin" setting was reconstructed simply observing the pattern given by the most reflective bodies. Deep incised and filled canyon were recognized in the slope. Early depositional stages, following an intense erosional activity, were characterized by linear trends and the deposition of small sized lobes at the channel termination. Detailed images allowed to distinguish even secondary branches or lobe tributary systems. Rejuvenation can result in the previous lobe incision by the feeder channel itself: further, a younger lobe will be deposited downward.

The analysis of the present Sea Bottom surface, allowed to obtain a model of the "basin to slope transition" physiography and of the active depositional systems, helping to understand similar subsurface elements.

Prospect recognition and analysis. The voxel connectivity function, implemented in the visualization software, enabled the direct detection of geophysical bodies. A number of objects were easily "captured" and analyzed by seismic character using the available attributes. Continuity, AVO fluid prediction and seismic inversion were thus used to obtain an attribute based quantitative prospect ranking.

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