Petroleum Systems Modelling of Presalt Source Rocks in Lower Congo Basin Angola

Abstract

The Lower Congo Basin is situated in the Central Salt Province, one of the most highly prospective areas for hydrocarbon exploration in western Africa. Presalt hydrocarbon potential has been established in shallow water areas of the basin in Congo and the Republic of Cabinda. Successful discoveries have targeted carbonates of the Toca formation, which is the Presalt reservoir. To investigate Presalt hydrocarbon potential in the ultradeep, we performed 2D petroleum systems modelling in seven transects across ultradeep water blocks 46 to 50 of Lower Congo Basin. This petroleum systems modelling focuses on the maturity of the postulated Presalt source rocks and relates it to the other petroleum systems elements, and relative timing of generation/expulsion, migration, accumulation and trap formation. Maturity modelling of the Presalt source rocks indicates a working petroleum system. The Neocomian source rock intervals mostly show high transformation ratio values in the deepest graben. The Barremian source rock is immature in some places but mostly above 15% transformation ratio (onset of expulsion sensu Pepper and Corvi, 1995) and becomes very high in the grabens. Vitrinite reflectance modelling of the Neocomian source shows that it has mostly passed the main oil window and some parts even reach the dry gas window. The Barremian source rock is mostly in the late oil window. Hence, modelling results predict that the generated (primary in-source cracking sensu Pepper & Corvi, 1995) hydrocarbons are of both liquids and vapour phase. Based on the results from 2D modelled transects, charge chance of success (CoS) maps were created by interpolating the charge CoS for all the modelled transects which are constrained by the sediment overburden map. The 2D petroleum systems modelling results indicate excellent hydrocarbon potential of the Presalt source rocks in ultradeep blocks of Lower Congo Basin.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015