Fault-Bounded Trap in Gamba Sandstones, Niungo Field, Pre-Salt South Onshore Gabon, Africa

Ferrand, N., R. J. Theunissen, Perenco, London, United Kingdom

Aggressive development of the Niungo Field by Perenco during 2003 has confounded the pre-existing geological models of the field. Most Pre-salt structures in onshore South Gabon (Rabi, Echira…) are mapped as a four way dip closed anticlines.and Niungo field was originally mapped in this way. Development of the field was almost abandoned after the fail­ure of wells three and four and due to the presence of H?S in the oil. After a new phase of mapping, a successful appraisal well in 2001 led to the installation of surface facilities capa­ble of treating the H?S. The field was brought on stream in 2002 and since then 13 new development wells have enabled a completely new structure of the field to be confirmed. A new fault bounded play along the margin of the Gamba-Dentale basin has been defined.

Mapping of Pre-Salt structures on seismic in South Onshore Gabon is very difficult due to salt collapse features and karstic surfaces which severely affect the velocity field and seis­mic image below the salt. Recent reprocessing and a velocity model driven by well control has helped to understand where the greatest uncertainty is present in the geophysical image. Magnetic data has also helped to define the basin boundary shape.

A history of the field mapping will be presented. The iterative process between the geo­physical and geological models as drilling progressed will highlight how our understanding of this field has changed allowing development to advance.