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Bob Cassie - Discovering Oil in Uganda

Discovery Thinking Forum, ICE 2015 Melbourne

Discovery Thinking Forum, ICE 2015 Melbourne


Discovering Oil in Uganda: Opening the East African Rift Play. Discovery Thinking talk given by Bob Cassie at AAPG International Conference and Exhibition (ICE) in Melbourne, Australia on 14 September 2015.

In the late 1990s the Lake Albert region was largely unexplored and of little interest to the petroleum industry. However, several factors made this area attractive to Hardman Resources and their joint venture partner, Energy Africa (both later acquired by Tullow Oil):

  • Attractive geology with signs of an active oil source, reservoir and seal;
  • Successful rift basin analogs existed elsewhere;
  • As there was little interest from other companies, it was possible to acquire a large exploration area with high equity and reasonable terms (including the exploration commitments).

However, the basin was remote, and the development economics were unclear.

Regional gravity and magnetic data suggested the basin contained up to 6000 m of sedimentary section. Multiple seeps had been identified around the basin, and analysis of the best known seeps indicated the presence of a lacustrine algal source and a mixed terrestrial and lacustrine source. The distribution of seeps suggested a widespread, mature source, and/or good migration. A comparison to other rift basins suggested a number of trapping styles, including tilted fault blocks in pre-and syn-rift sections and drape over fault blocks, could be expected.

Executing an exploration program in this remote area, with little access to services and support, was challenging. In 2003, an initial 1589 km seismic survey was recorded across the whole lake by Hardman, in co-operation with the University of Syracuse, using a converted fishing boat and a small acquisition system. This provided a very cost effective overview of the basin and identified a number of leads. Subsequently, an onshore and transition zone seismic survey was acquired to define prospects for drilling.

All the identified prospects shared a common risk, seal against basement faults. The largest prospect would have required a deviated well drilled from shore, through a major fault to a bottomhole location in the lake – a high risk option for an initial well in a remote area. The joint venture, therefore, decided to test the play concept with simple vertical, onshore wells and drilled both the Mputa and Waraga prospects.

The success of the initial wells demonstrated the potential of the basin and subsequent exploration has discovered 1.7 billion barrels of oil in 17 fields. More than 80 exploration and appraisal wells have been drilled with a 90% exploration success rate.

Lessons learned include:

  • Be prepared to do something different (in terms of the areas to explore and how to do it);
  • “Cautious optimism” is useful (don’t talk yourself out of a project too early!);
  • Sometimes it can be easier to execute a program than you might first think – particularly if you are prepared to do something different.

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