Potential Field Analysis of the East African Rift in Eastern Tanzania—Guiding Seismic Survey Planning

Abstract

Recent oil discoveries in the Kenyan Lokichar Basin, on the eastern branch of the East African Rift System, indicate more extensive oil potential within the rift systems than previously thought. A combination of legacy aeromagnetic data together with proprietary airborne gravity and magnetic surveying over the Kilombero Trough, Kilosa Basin, Kidatu Basin and Pangani Basin in eastern Tanzania provided the base geophysical datasets to investigate the potential for thick accumulations of Tertiary and or Karoo sediments within these sections of the eastern branch of the rift. Previous geological investigations suggested basin depths of 2 km to 8 km are possible in the region. The objective of the potential field surveys was to identify thicker prospective sections of the Tertiary basins for evaluation by seismic surveying. Regional structural interpretation of the legacy aeromagnetic data identified major long-lived fault systems controlling intra-rift basin development, and provided a qualitative assessment of depth-to-basement, constituting a significant advance in the understanding of the basin evolution than could be gleaned from satellite spectral and topographic data. Naudy and Euler automated depth-to-basement methods were employed in conjunction with manual 2.5D forward modelling on the proprietary datasets to quantitatively evaluate basin depths and geometry. Using density contrasts typically expected for Precambrian basement, Karoo and Tertiary sequences, 2.5D forward modelling of the airborne gravity data showed the potential for up to 7 km of basin sediments within the rift, and highlighted the possibility of Tertiary rifting within the Kilombero Trough. Follow up 2D seismic work has confirmed the prospective basin geometry, and has identified intra-basin structures of exploration interest.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015