Sublacustrine channel-levee system of the Caruaçu member, southwest Recôncavo Basin, Bahia, Brazil

Abstract

Caruaçu Member (Maracangalha Formation) is an oil and gas producer in Recôncavo Basin, Brazil. This unit crops out in the coast of Todos os Santos Bay, near the Aratu Navy Base, in the Great Salvador, and in the Bom Despacho Ferry Station in the Itaparica Island. Caruaçu shows channel-fill and proximal levee facies in the first locality and sheet sands in the latter. In the southwest of the Cassarongongo and Taquipe fields area, these sandstones can be recognized in logs and have characteristic reflections in seismic lines. The channel cut is represented by white (negative polarity) reflections and channel filling is marked by black (positive polarity) reflections, which onlap the white ones. Levees are marked by elevations in the channel borders, which are channels flowed down the slope of the Maracangalha deltaic complex and sporadically formed crevasse-splay deposits. In the southeast Recôncavo, channels flowed into a large splay area, whose sheet sands coalesced laterally and vertically into thick sand bodies. Caruaçu sandstones form unconventional oil and gas traps as they frequently do not present oil or gas/water contact. In the deepest part of the basin, they behave as tight-gas sands.