Abstract
Source rock predictability in Agbada Formation of Niger delta, Nigeria was investigated for an offshore well. This was made possible by the use of composite logs that comprise of gamma ray, resistivity, and neutron and density logs. The fundamental principle was based on both the interpretation of log suite and the concept of sequence stratigraphy in the identification of prolific source beds. Source rocks were identified on the logs based on sequence stratigraphy principles by identifying the maximum flooding surfaces (MFS), flooding surfaces (FS) and condensed sections (CS) which are the saltiest and organically-rich facies. The relative increase in resistivity values associated with high gamma ray, combined with wide separation between the neutron and density log signatures compared with the underlying and overlying facies could depict a source rock. Mature source rock can be identified by the anomalously high resistivity values might be due to the effect of the presence of oil droplets left behind by hydrocarbon migrated updip into the reservoir sandstones. Source rock facies are characterized by high gamma ray values and wide separation of the neutron and density logs (bell-shaped) which could be due to the presence of radioactive elements probably due to the absorption of such elements by the benthic microfaunal, Necreites, Zoophycus and other deep-water burrowing organisms present in the substrate.
Keywords: Source rocks, wireline logs, sequence stratigraphy, resistivity, gamma ray, wide separation