Print this pageAptian Sequence Stratigraphy of the Southeastern Border of the Potiguar Basin, Rio Grande Do Norte, Brazil, Comprising Several “Pre-Salt” Oil and Gas Occurrences
The onshore Potiguar Basin, Rio Grande do Norte State, Northeastern Brazil, is well known to have an important petroleum system in the Late Aptian Alagamar Formation. STARFISH OIL & GAS participated in the drilling operation of four wells in the Southeastern border of the basin, discovering oil and gas in sandy reservoirs belonging to the Alagamar Formation (Late Aptian). Aptian Age is known to be marked by one of the largest eustatic rises in the geological record which influenced the stratigraphy of a series of basins in the world. In the Potiguar Basin, the marine invasion was made by at least six minor transgressions. Throughout dynoflagellate correlation, it is estimated that marine waters came from the Central Atlantic Ocean or even from the Tethys sea. Each transgression marks a maximum flood surface which constitutes a fourth-order genetic sequence boundary (sensu Galloway, 1987). Marine invasions were ephemeral events. The younger one is more important and marks the boundary of a third-order genetic sequence. Soon after each minor transgression , salty lacustrine conditions (“lac-mer”, sensu Hsü, 1973) dominated, which in an arid climate developed evaporites. Systems tracts along this depositional span are made of alluvial fans and its braided fluvial and deltaic deposits (Upanema Member), isolated lagoons with development of stromatolites , tepees and evaporites, plus shoreface “tempestites”, and lacustrine organic-rich shales (Ponta do Tubarão Beds). The highstand systems tract of the third-order sequence is made up by deltaic deposits of the Galinhos Member. Oil and gas are found in the Upanema Member in fairly- good reservoir conditions. Truly marine conditions are developed only in the Albian Ponta do Mel Formation.
AAPG Search and Discover Article #90100©2009 AAPG International Conference and Exhibition 15-18 November 2009, Rio de Janeiro, Brazil