Abstract: Temperature and Maturation 2-D Modeling in Southern Campos Basin

Coelho, D F.S. - Petrobras/E&P; Johansen, H. - Geologica A. S.

This work was carried out to better understand the temperature, maturation history and timing of hydrocarbon generation with respect to reservoir deposition, considering the complexities that arise when the salt structural evolution is a major player in the geologic history of an area. For that, we made use of a 2-D geologic modelling package, which allows a realistic structural reconstruction of the geology and consequently, thermal history, of an area. Figure 1, shows the geological section used in the modeling. It takes into account the pillows, domes and diapirs of the regional salt layer as well as the heavily faulted carbonate platform. The complex structuring can have a big impact on the thermal conductivity and heat flow distribution, thus affecting the temperature and maturation history.

Bottom Hole temperature and vitrinite reflectance were used to constrain present day temperature and heat flow, as well as the maturation history, in the southern part of the basin. A uniform McKenzie Model was presumed for the heat flow history. The thermal conductivities were obtained from acceptable ranges in the literature since this data was not available.

The structural restoration of the section, including the heavily faulted Albian carbonate platform, was made assuming a vertical shear model. The salt (Late Aptian) restoration was based on the assumption that salt volume was conserved along the section and that the salt depocenter would be located over the depocenter for the Early Aptian sequence, thinning to a 200m thick salt in the western limit of the cross-section and to zero in the eastern limit. The salt in the Salt Domes Province was restored back to previous geologic times by first displacing the mass of the salt domes and finally the regional salt mass. Sensitivity analysis was carried out on several geological parameters relevant for the thermal maturation of the area.

The results show that the salt distribution evolution was the main geological parameter controlling the thermal evolution of the pre-salt sediments. Its impact in the post-salt sediments was minor. Results also suggest that the salt layer formed a regional seal until the end of Late Cretaceous. Salt windows, providing migration pathways, were effective only after Late Oligocene. The Early Aptian pre-salt source rocks, if present, are expected to be the main mature source of petroleum in the deep water region.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil