Abstract

The Recincavo Basin is a Late Jurassic-Early Cretaceous asymmetric rift system in Northeastern Brazil. Its sedimentary column of up to 8,000 m thickness can be divided in (1) a fluvial-aeolian-lacustrine pre-rift sequence and (2) a syn-rift sequence, composed of lacustrine, deltaic and fluvial shales and sandstones. The syn-rift lacustrine shales of the Neocomian Candeias Fm. (Gomo Mb.) have been recognised as the most important source interval, containing type I kerogen.

Aiming to better understand the timing of petroleum generation and accumulation, source rock expulsion efficiency, migration pathways and related compositional changes, an integrated geochemical and basin modelling study has been performed in the Recincavo Basin. Petroleum potential and compositional kinetics have been evaluated on source rocks of the Gomo Mb. with TOC ranging from 0.5 to 5% and vitrinite reflectance from 0.4 to 1.0%. Three dip cross sections have been modelled with the Temiscomp 2-D software. Geochemical data have been used as input parameters and to calibrate modelling results. Temperature, pressure, vitrinite reflectance, GOR and petrophysical data have also been used to constrain modelling.

Two major styles of petroleum migration have been observed: (1) the Late Jurassic pre-rift accumulations, characterised by downward migration of petroleum from the source rocks to underlying carrier beds followed by updip secondary migration, with normal faults acting as conduits; (2) the syn-rift Late Neocomian reservoirs, with lateral and vertical migration from source rocks to overlying reservoirs.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah