- Copyright © 2002 Society of Exploration Geophysicists
In July 1995, VAALCO Energy was awarded the Etame Marin permit which encompasses 3074 km2 in the northern portion of the Congo Basin offshore southern Gabon (Figure 1). The Congo Basin developed and evolved as a result of rifting and subsequent drifting of the African continent from South America. An upper Aptian salt series divides the underlying syn-rift sediments and structures of the basin from the overlying drift-sag sediments, which have been structured by post-Albian salt tectonics. The dominant salt features are subparallel “salt walls” that extend 10–50 km.
Between 1969 and 1992, various operators (including Shell, Elf, and Esso) drilled 25 subsalt tests in the area on the basis of 2D seismic. For the most part, their primary objective was the middle Aptian Gamba sandstone reservoir, with porosities of 25–30% and permeabilities of 1–3 darcies. These early exploration efforts accumulated 6000 km of 2D seismic and discovered two noncommercial oil fields of approximately 10 million barrels each. Production on trend from this world class reservoir includes the onshore Gabon fields of Rabi-Kounga and Gamba-Ivinga (estimated ultimate recovery, ∼1.2 billion barrels).
VAALCO and partners acquired a 400 km2 3D seismic survey in 1997 and drilled the discovery well for Etame Field in June 1998 on the basis of poststack depth-migrated data. The discovery well tested 3700 b/d from a 13-m interval in the Gamba sandstone. A subsequent well, although successful, reinforced the need for better seismic resolution below the salt walls and a better velocity model to delineate the low-relief drape structure that defines Etame Field. Prestack depth-migration processing was performed on the 3D survey by Paradigm Geophysical in 1999, and two very successful appraisal wells followed in 2001.
Geologic and exploration history
VAALCO Energy is the operator of the Etame Marin block and …