A field study report of the Semliki basin in the Albertine Graben, Western Uganda
Abstract
The field study is conducted for 12 days in the Kibuku area within the Semliki Basin in Western
Uganda the area which lies onshore south of Lake Albert basin on the eastern side of the
Albertine Graben which lies in the western branch of the East Africa rift system with the rift
flanks rising to approximately a height of 400m above the Graben on the eastern side. It is
bounded by an escarpment to the east and south and River Semliki to the west. These rift flanks
are underlain by the Basement Complex rocks which have undergone intense metamorphism that
led to the formation of vast types of structures. This report comprises a detailed compilation of
findings from the field and is made up of seven chapters that give a detailed account of the
objectives, materials and methods, lithology and stratigraphy, basin and facies analysis,
structures, Geophysics of the Semliki basin and discussion of results which help in understanding
of the petroleum play of the area. Many different facies types are identified in the area, as well as
their significance in the formation of good reservoir rocks and seals. The sedimentary structures
include faults and plunging folds (anticlines) that would be good structural traps for
hydrocarbons. The presence of hot springs with in the area are indicative of the presence of high
enough geothermal gradients for oil maturation. The geophysical logs that are interpreted imply
that the sediments are thick enough and comprise of alternating layers of thick sand stones
overlain by clays. Vast structural and stratigraphic data collected are then analyzed to make
conclusions about the petroleum potential of Semliki basin where the basin is generally filled
with Middle Miocene to recent age sediments exhibiting a fining upward sequence (characteristic
of fluvial systems) from conglomerates (overlying the basement rock) to sands to silts up to
clays. It is structurally wedge shaped and majorly comprises faults, joints, laminations and
bedding planes, cross beds, foliations, quartz veins, unconformities, and soft sediment
deformation structures. It is concluded that the study area has a good working petroleum system
evidenced by the abundance of excellent reservoirs, regionally mature source rocks, traps, intra
formational and regional seals as well as hydrocarbon-migration pathways in the basin.