Scarparo Cunha1, Armando Antonio1, Seirin Shimabukuro1, Rogério Loureiro
(1) PETROBRAS, Rio de Janeiro, Brazil
Seismic and geophysical log interpretation coupled with chronostratigraphic framework is the most commonly used technique for stratigraphic analysis. Despite its usefulness, this methodology does not always provide a sufficiently high resolution. In order to improve the stratigraphic resolution some additional non conventional techniques are required. In fact, chemiostratigraphy and cyclostratigraphy allow resolutions as high as 100 ka on a field-reservoir scale. The multiple-scale technique consists of transferring the stratigraphic correlation from basin-scale to field-reservoir scale by integrating different methodologies, as shown in the example below. The seismic and well log signature of lower Oligocene Braarudosphaera Chalk has been recognized throughout the subtropical South Atlantic Ocean. This stratigraphic marker is characterized by its paleoecological and biochronostratigraphic significance and 13C - 18O content. Because of its unique chemical, physical and paleontological signature the marker provides a reliable datum on both regional and field-reservoir scales. In some areas, the Oligocene section above the Braarudosphaera Chalk can be subdivided into biostratigraphic units ranging from 1 to 0.3 Ma in time span. These biozones can be subdivided by using elemental concentration and 13C - 18O logs, which show close relationship with biofacies and conventional lithological-geophysical logs. In this way, the resolution obtained can reach values of 0.1 Ma or more. Besides, the application of a high-resolution cyclostratigraphic approach permits to estimate average deposition and accumulation rates for these chemical units, which are usually composed of rhythmic deposits.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.