SEISMIC GEOHISTORY AND DIFFERENTIAL INTERFORMATIONAL VELOCITY ANALYSIS IN THE ANAMBRA BASIN, NIGERIA

Abstract

The methods of seismic geohistory analysis and differential interformational velocity analysis have been applied using datafrom some interpreted seismic sections within the Anambra basin. These two techniques for basin analysis have been appliedin the basin in an attempt to aid the identification of anomalous velocity zones. Results from the seismic geohistory analysis indicatethat some faults arising probably from compressional stresses, due to the upliftment of the Abakaliki anticlinorium, were observed to be significant mostly in the northern and southeastern regions of the basin. These faults which originated in the Santonian are probably related to the first folding episode in the evolution of the Benue Trough. The Maestrichtian / Campanian faults observed towards the north of Anambra River-3 well may also have been influenced by these stresses or are directly related to the Post-Maestrichtian folding episode in the Benue Trough. The fault system KP identified on the seismic section is a Pre-Eocene event which cuts across from the south of Okpo-1 and Nzam-1 to the north of Iji-1 well. Sediments to the north of Nzam-1 well site have experienced more faulting during the Lower-Maestrichtian times. Fault systems that occurred after the Paleocene times are more prominent in the southern parts of Nzam-1 towards Iji-1 well sites. Generally most ofthe major faults occurred in the Paleocene. The major 'DIVA' anomaly observed southeast of Anambra River-1 well correlateswith the zone of overpressures within which liquid hydrocarbon, water and gas have been discovered in the basin. The Maestrichtian to Paleocene sediments in the southern and mainly in the southwestern sector of the Anambra basin should be the major sedimentary strata with liquid hydrocarbon potentials, whereas the Lower Cretaceous and particularly the Santonian sediments exhibit the highest potentials for gaseous hydrocarbons.