A focus on the thermal history of the East African Margin  
 
providing new direct constraints for exploration
 
 

   

Quantitative thermal history analysis of selected areas of Kenya, Tanzania, Madagascar & Mozambique will answer key questions for exploration
 

 

Proposed work program – expressions of interest sought
May 2004
 

A focus on the thermal history
of the East African margin

EXPRESSIONS OF INTEREST SOUGHT

  Quantitative thermal history analysis in a frontier margin – securing a basic understanding of the real limits to source rock maturation and burial histories  

 

Introduction


Following discussions with prospective key players in petroleum exploration on the east African margin (principally Kenya, Tanzania, also Mozambique and Madagascar), Geotrack proposes the Thermal History Reconstruction (THR) of selected wells and possible outcrop sections in this region. THR is a method employing an appropriate suite of techniques designed to define by direct measurement key thermal parameters for constraining basin evolution – such parameters are:

  • timing of maximum paleotemperature(s),
  • magnitude of heating,
  • amount of erosion,
  • heatflow (or gradient) history, and
  • reliability of conventional maturity data.

Although some models for petroleum systems for the region have been in the public domain for many years, none has been underpinned by firm constraints on the thermal history, using such specialist techniques as AFTA (Apatite Fission Track Analysis), and U-Th/He dating. Other important complementary techniques are VR (vitrinite reflectance) and fluid inclusion data. Integration of these new constraints with current basin models and local geological knowledge will be key to refining petroleum systems for the prediction of commercial petroleum occurrences.

Statement of the problem – e.g. Kenya and Tanzania

 

Despite the uncertainties facing frontier exploration around the world, strong enthusiasm for portions of the east margin of Africa is driven by the presence of prolific high-quality reservoirs and potential world-class source rocks.
Both structural and stratigraphic plays are believed to be present, though greater confidence in various structural plays awaits acquisition of additional seismic data to verify structural details. It is speculated that portions of areas like the Simba-Pemba trend, affecting both Tanzania and Kenya (figure to right, taken from Antrim PESGB/HGS abstract publication) has acted in the past as a paleo-high, with significant burial and heating on the flanks. The presence of seeps on Pemba Island serves to reinforce a model in which migrating hydrocarbons (during the Paleogene) were reservoired in Cretaceous and/or Tertiary units at that time. Also central to this model is denudation of the continental margin supplying the overburden and heating mechanism to the offshore source rocks, the timing, location and magnitude of which have not been quantified.
Other features along the margin, such as the Davie Inversion Ridge off Kenya, are also speculated to represent important inversion structures that may serve as either valuable foci for hydrocarbons, or alternatively, offer additional risk to the play profile, by having reduced the integrity of the trap at some time after entrapment.
In summary, petroleum system models in this area rely strongly on assumed values for various key basin elements … such as sediment supply, basin inversion (timing and magnitude), and heatflow and maturity history. Great advances in constraining these elements should be expected by using high-quality thermal history analytical tools, based on AFTA, thus ultimately adding far greater confidence to our understanding of the petroleum system(s).

 

Study logistics

Relevant government agencies from Kenya, Tanzania, Mozambique and Madagascar have been contacted and all have offered their support, and access to available well material and relevant outcrop samples.
This study, undertaken in collaboration with Alconsult International (Calgary), which has considerable exploration experience worldwide, including E. Africa, will commence with subscriptions from at least two companies. It is anticipated that the “study” will in fact consist of a number of single well studies from various basins, or a collection of outcrop samples, using initially both AFTA and VR. Complementary techniques, U-Th/He, ZFTA and fluid inclusion data, will complement the initial data set, as demanded. The sample material will be collected in Kenya and Tanzania (Mozambique and/or Madagascar), and expedited to Geotrack’s laboratory in Melbourne. Well information and more regional background information have been promised from each of the host countries.
We are presently refining the well selection list (and onshore localities) based on advice from interested parties and invite your suggestions.

 

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