Mamba: Supergiant Gas Discovery After 60 Years of Exploration in East African Coastal Basins

Orsi, Marco
[email protected]

East Africa coastal basins record recent fantastic exploration success after long neglect by the industry. Eni is among the major players having discovered in 2011-12 the Mamba gas supergiant in the Rovuma Basin of Mozambique with an estimated potential of 75 tcf in place. Exploration in East Africa started during the 50s, why the big discoveries came 60 years later?

The onshore and shallow water exploration carried out from the 50s to the 80s brought only few gas discoveries at that time deemed not commercial. The lack of oil discoveries was probably the main reason that discouraged further investments and the offshore basins remained virtually unexplored. The long sleepy phase of exploration lasted for 20 years, which ended in the first years of the 21st century. New geological ideas and the opportunity given by LNG technology to export gas towards the growing pacific markets determined a new surge of interest in the East African coastal basins.

In 2006 Eni was awarded the license Area 4 in Mozambique thus becoming one of the first E&P players to enter the virtually unexplored Rovuma Deep Water Basin. It was not the first time for Eni in the Rovuma where in 1982 Agip (now Eni) discovered the Mnazi Bay gas field in the Tanzanian onshore that until 2010 remained the only discovery in the basin.

The experience gained from the exploration in Tanzania during the 70s and the 80s and the few data acquired by other operators in Mozambique, convinced the geologists of Eni that Area 4 was located in the sweet spot of the basin. After the first reconnaissance 2D acquired in 2008, the huge potential of the tertiary gas play became evident. A high quality 3D seismic survey was then recorded in 2010 over the main prospect called Mamba, thus enabling the detailed definition of the geological model and the de-risking of the prospect.

Mamba South 1, the first well drilled in 2011 by Eni and its partners Galp, Kogas and ENH, encountered a total of approximately 300 m gas pay in Eocene and Oligocene reservoirs with outstanding quality and thickness thus confirming the validity of the pre drill geological model and the huge potential of the discovery. Following the success of Mamba South 1, an aggressive drilling campaign was implemented aiming to conclude the exploration and appraisal phase by the first half of 2013. Up to February 2013, 8 wells were successfully drilled confirming the potential of the Mamba Complex in Area 4 at 75 tcf of gas in place.

The Mamba gas discovery is an excellent example of how new ideas, new technologies and changed economic environment can lead to extraordinary exploration successes in basins long neglected by the industry.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013