Burundi

Positioned between 2o30’and 4o30’ Latitude South and between 28o50’ and 30o53’30’’ Longitude East, Burundi is located in East Central Africa, bordered to the North with Rwanda, to the West by the Democratic Republic of Congo, and to the East and South by Tanzania, with a total surface area of 27,834 sq.km, of which 92,2% is land and 7,8% is water.

Burundi Exploration Activities

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Introduction

Burundi Map of Petroleum explorationOften called “The Heart of Africa,” Burundi is located between 2°45’ and 4°30’ latitude south and covers an area of 27,834 square kilometers. It is a landlocked independent state which borders with Rwanda, Tanzania and Democratic Republic of Congo, thus forming part of the Central African Region.  

Various studies have been conducted since 1959 for petroleum exploration both on the Rusizi Basin and in the Lake Tanganyika Basin. These Basins are part of the East African Rift System and are located between Burundi, Democratic Republic of Congo, Tanzania and Zambia. This Rift System is dated from Cenozoic (Tertiary) and is divided into two branches : the Eastern arm and the Western arm. The Lake Tanganyika and the Plain of Rusizi belong to the Western branch and consists of sedimentary basins marked by deep Lakes (Malawi, Tanganyika).

In Burundi, those basins cover an area of 2,968.1 km2. Geological studies, gravimetric, aeromagnetic and seismic surveys have been conducted in the two basins and the average sediments thichness is estimated to be more than 3,000 meters.

The exploration area of Rusizi and Lake Tanganyika basins have been divided into four blocks : A (793,1 km2), B (697,1 km2), C (664 km2) and D (813,4 km2). Block A is on Rusizi basin which is an onshore while B, C and D are offshore in Lake Tanganyika basin from North to South respectively.

The Government of Burundi continues to encourage oil companies to invest in petroleum exploration. It is also reviewing the Petroleum Code dated in 1976 for attracting more investors.

Blocks C & D are granted to A-Z Petroleum Products Limited and Surestream Petroleum Limited respectively for exploration. Since the decrease of petroleum crude prices, the field works are suspended but the companies plan to conduct a 2D seismic campaign soon.

Burundi is sufficiently watered, rich with an abundant hydrology and rainfalls out pours for nine months per annum, with a subsequent  ecosystem favoring tourism.

Burundi presents 5 topographical zones:

  1. Rusizi /Tanganyika Plain;
  2. Mumirwa region;
  3. Congo Nile Ridge: including the great secondary forest of Kibira;
  4. Central plateaus featuring rolling hills; and
  5. Depressions of the East and North East featuring tree-dotted savanna;


Location of Burundi in the East African Rift System

Sedimentary Basins in Lake Tanganyika

  • On same trend as Lake Albert discoveries (Uganda)
  • Age of Basin Late Miocene to Recent
  • No volcanics
  • Similar structural regime to lake Albert
  • Neogene exceeds 3km in potential kitchen areas
  • Seeps on western side of basin


History of Oil Exploration in Burundi

  • 1983-1984 : ‘Probe’ academic seismic grid acquired by Duke University (reprocessed by Surestream Petroleum in 2011)
  • 1984 : Kenting Aeromagnetic survey acquired
  • 1984-1985 : Project Geo-Rift studied lakebed geology,  supported by Elf Aquitaine
  • 1986-1987 : Amoco acquire seismic onshore and drill 2 shallow dry wells
  • Neogene  section through all sandston failed due to lack of seal
  • Expect rapid geological changes into lake to south with incoming of seals and source rocks

Petroleum related activity concentrated in 1980s, initially academic work (seismic and lakebed studies) then licence held by Amoco in 1986-7 resulting in two stratigraphic wells in shallow extension of basin onshore. Probe seismic acquired by Duke University forms main geophysical database accompanied by Kenting aeromagnetic survey. Followed by long period of inactivity in 1990s and early 2000s prior to discovery of Lake Albert fields on trend.


Lake Tanganyika Tectonic Elements

Lake Tanganyika covers a set of basins – it is not a single basin. These are of different ages. The presence of Permo-Triassic section onshore in DRC suggests the southern basins are composite rifts of Permo-Triassic and Neogene age while the Burundi wells suggest the N-S trending northern basins are entirely Neogene in age. Burundian waters contain parts of two basins as outlined above. Sedimentary isopachs are from maping of Project Probe seismic.

  • Lake Tanganyika contains several basins separated by Basement Highs;
  • Northern basins are Neogene, southern basins date in part to Permian;
  • Burundi waters cover two of these basins:
    • Ruzizi Basin, poorly controlled by seismic, up to 4km of section indicated by aeromagnetics
    • Kigoma Basin, well controlled by seismic, up to 5km of section in Congolese waters.



Northern Lake Tanganyika Tectonic Elements

The Ruzizi Basin, which is poorly defined by seismic, is separated from the Kigoma Basin by the large Ubwari Basement High, an extension of the Ubwari peninsula in DRC. Faulting in both basins follows ancient Basement trends and there are discrete areas of structuring where these trends overlap. Thus Neogene faults only a few million years old are controlled by lines of Basement weakness 2 Billion years old.

Northern Lake Tanganyika Seismic findings

The Probe seismic varies significantly in quality and is generally better in the Kigoma basin from which this line is taken. This clearly illustrates a deep half graben in the west of the basin (in DRC) shallowing into a series of fault blocks in Burundi Block D similar to those which contain most of the Lake Albert reserves. Seismic geometries and facies allow a three fold subdivision of the sequence, with the progressive evolution of a deep basin illustrated. Reservoirs are considered most likely within the basal pre-rift sequence, which is transparent in nature and is thought to be filled by fluvial sands. The overlying rift sequences are likelyt o contain lacustrine ource rocks similar to those being deposited on the lake bed at Present Day.

 

Geological History of Lake Tanganyika, Burundi Sector

No seismic tie is possible at this stage to the onshore wells but dating of these sequences can be predicted by integrating the study of lakebed cores, from which Recent sedimentation rates can be calculated from Carbon , dating and assuming such sedimentation rates can be extended into the past. This suggests the basin is between 8-15 Ma old, thus comparable with Lake Albert.
  • Age of basin thought to be comparable to Lake Albert from extrapolation of sedimentation rates (Carbon Dating of cores)
  • Transition through time from shallow sag basin to narrow deep rift
  • Best reservoirs likely to underlie source rocks as in many other rifts

History of East African Rift System

Northern Lake Tanganyika thus seemed to be one of a series of rifts formed in the Western Branch in the Late Miocene. The area of rifting expanded with time but it is these earliest rifts that are thought to be the deepest and most prospective. Note that the rift shoulders were not uplifted in this interpretation till the Pliocene and thus the topography seen around Burundi is thus very young.

Red volcanics

  • Basin developed in Mid-Late Miocene along with Lake Albert as one of earliest Western Branch rifts
  • Growth of much of rift topography is Pliocene or younger, as in Lake Albert 


South-North Play Cross-Section

A south to north section illustrates plays in both the Kigoma and Ruzizi Basins, plus the major high which separates them. Plays are more speculative in the Ruzizi Basin due to poor seismic definition with depth to Basement controlled by aeromagnetic interpretation. Plays in the offshore basin are also dependant on the incoming of source rocks and seals not seen in the onshore Ruzizi 1 well, as is seen with the Present Day facies distribution below the lake.

  • Section through all Burundi blocks and basins from south to north
  • Ubwari High separates Kigoma and Ruzizi Basins
  • Play types in Ruzizi Basin likely controlled by sand input from palaeo-Ruzizi river : expect rapid facies changes and incoming of source rocks and seals south of Ruzizi 1 onshore well (illustrated below)

Possible Oil Kitchens

Heat flow data and analogue to Lake Albert implied circa 2.5 km overburden required to mature source rocks (need to review temperatures in Burundi wells). Greatest confidence in Kigoma kitchen shown as well defined on seismic and associated with seeps. Oil should migrate eastwards into southern Burundi waters. Small kitchens possible in north (Ruzizi Basin) but depth to Basement very uncertain – need more seismic to confirm


The available data around Lake Tanganyika suggests high geothermal gradients that will mature the proposed source rocks. Geothermal gradients in the two onshore wells are in the region of 65 deg C/100m, which would mature source rocks at around 1500m overburden. The young nature of the oil from the seem (next slide) suggests very high geothermal gradient in that region. Heat flow data from Lake Rukwa suggests an overburden of 2400m will be sufficient. This data, together with seep observations, indicate that oil will be generating in the regions shown

  • Other East African Rift Basins indicate that a sediment thickness of circa 2500m is required for oil generation
  • However, high geothermal gradients in Burundi onshore wells (>60 deg C/km) suggest maturity may be attained at around 1500m
  • Deep kitchens identified that should charge Burundian acreage within deepest parts of basins in Congolese sector


Oil Seeps in Congolese Waters Opposite Burundi

A well known oil seep occurs on the surface of the lake in Congolese waters opposite Burundi Block D. Illustrations here are a satellite image of the slick resulting from the seep and a close up of oil iridiscescence taken from a boat. The oil has been analysed and been shown to be a true oil but Carbon Dating suggests the source rock from which is originates must be very young (Pleistocene). The seeps has been known to be active from the arrival of the first explorers in the area and tar balls were known to be washed up on the beach at the Ruzizi river mouth in the early 1990s. The sustained nature of the seep indicates a large thermal anomaly and kitchen area and the data also proved deeper source rocks can be expected to be mature.

  • Proves petroleum system
  • Carbon dating indicates a shallow young source rock associated with a thermal anomaly.
  • Has been active throughout historical times, estimated 10MMbbls spilled into lake
  • Thought to lie over fault plane but must be charged by extensive source rock and thermal anomaly


Recent and Future Activity in Burundi

  • 2008-2012 : Blocks A-D awarded
  • 2013 : Planned high quality seismic offshore using converted Tanganyika Explorer vessel from Bujumbura

Environmental and Social Impact Assessment

  • Operations did not commence until a full Environmental and Social Impact Assessment was undertaken of all planned seismic and lake-bed coring operations
  • Close cooperation with Lake Tanganyika Authority representing all countries bordering lake
  • Risks were identified and mitigating measures applied , e.g. no seismic operations at night due to risk to fishermen.
  • Other lake operators are now undertaking similar studies