Seismic stratigraphy of the Campanian-Maastrichtian section of the Calumbi Formation in the Carapitanga field (Sergipe-Alagoas Basin)

Abstract

Oil and gas reserves from Calumbi Formation are partially preserved in the Carapitanga field, mostly in deposits of Campanian and Maastrichtian age rocks of the Sergipe-Alagoas Basin, a brownfield in the northern area of the basin. Despite their important role in regional hydrocarbon production, the depositional sequences of the field have been little discussed in academia. In order to contribute to the deposition sequence models of the Upper Cretaceous, the available field seismic was analyzed from the perspective of Sequence Stratigraphy concepts. The results suggest three depositional sequences of short duration (3 – 10 Ma), with an imbalance between ups and downs, which contrasts with the assumptions of sequence models. These are distributed in three canyons up to 10 km wide, 282, 202 and 102 m thick, respectively, located in the Pre-Campanian, Campanian and Mastrichian transition. The first sequence is formed by four system tracts, with small imbalance between two transgressive events of shorter duration compared to two regressive events, which record the sedimentation of low and transgressive tracts, corresponding to the best candidates for reservoir rocks of the field. The second, younger sequence preserves three events of regression and one of transgression; and the third sequence has similar behavior, but with a longer fall duration. The base level variation pattern is not very harmonic and contrasts with the sine curve adopted for prediction of depositional geometries in passive margin basins and with the models interpreted to the north of the basin, where four sequences were identified. The five recorded peaks of fall appear to be related to the high frequency glacioeustatic fluctuations of the Upper Cretaceous.