Seismic Stratigraphy Analysis and Hydrocarbon GenerationPotential of the Late-cretaceous–tertiary Formations From the Coriole Subbasin (Somalia Coastal Basin)
Abstract
The Coriole basin is the fifth largest sedimentary basin developed on the onshore of Somalia,
between larger Mudugh basin in the north-east and Juba-Lamu basin, at the south-west. It also
has a relatively thick infill (> 5 km) of sediments belonging to the Mesozoic and Cenozoic
which might have created favourable conditions for the development of the Petroleum system
elements (source, reservoir, seal, trap and migration). The major purpose of this research was
to create a seismostratigraphic framework and determine the structural style of the Coriole
basin that controls the hydrocarbon entrapment configuration within the thick Cretaceous to
Recent sedimentary infill through the interpretation of 2D seismic data of a total length of 205
km. This kind of research has never been carried out before, and therefore, it has both academic
and practical interest. To achieve these objectives, we integrated the interpretations from seven
(7) 2D seismic profiles with well top formation data obtained from Afgoi-2 well. This enabled
to map the extent of eleven (11) seismic horizons. In order to determine the maturity of the
Upper Cretaceous rocks and Tertiary rocks and to evaluate the time of hydrocarbon expulsionmigration-
accumulation, a series of Time Temperature Index (TTI) burial history curves were
generated and analyzed. TTI results demonstrated that the Jesomma-Auradu Equivalent
Formation began to expel some crude oil approximately 9.48 Ma (Tortonian stage Late
Miocene), implying that these formations with average TOC (0.5 wt%) values may have
possibly generated normal-light oil and wet gas condensate products, and are still in the early
oil generating phase (Waples, 1985). The overlying stratigraphic layers are generally immature
where the Obbia and Scebeli, and also Somal formations have TTI values ranging from 1.3003
to 3.089. TTI modeling was expanded on other neighboring well sections, including Merca-1,
Coriole-1, Afgoi-1 and demonstrated common temporal source rock maturation trends and
hydrocarbon expulsion dynamics. The TOC values from Afgoi-2 were used to identify three
source rock intervals. These are: the Jesomma-lower Auradu formation interval (9190'-13710')
with an average TOC value of 0.86 wt % and Seriole-Auradu transition – lower Somal Sand
Member interval (4920'-7330') with an average weight TOC content of 0.90 wt % and Somal
formation with an average TOC of 0.39 wt%. According to our TTI calculations, the first two
intervals are mature and still capable of producing hydrocarbons (light oil products). Their
thicknesses increase towards the Somali Coastal Basin's offshore area. The third source rock
(Somal-Scusciuban-Somal Transition Formations) interval is mostly immature and has no HCproducing
potential. This integrated study revealed that the Coriole section of the Somalia
Coastal basin has three hypothetical (fictional) petroleum systems: a) Jesomma-Auradu
Equivalent (Sagahley-Marai Ascia) Petroleum System; b) Scebeli/ Obbia-Auradu Petroleum
Systems and c) Somal Petroleum Systems. Among them, the most promising in generating
hydrocarbons is the first one, the Jesomma-Auradu-Jesomma Equivalent Petroleum System,
consisting of mature source rock intervals and good quality reservoir. The Jesomma and
Sagahley Marai Ascia formations offer two types of reservoirs: sandstone and carbonate. The
generated isopach and isochore maps enabled us to map the deformations with potential traps
and identify the possible primary and secondary hydrocarbon migration pathways. The results
demonstrated that the area has been affected by wrench tectonism. This research offers an
integrated approach that helps better understand the reasons and explain why the Afgoi-2 well
failed to make any commercial hydrocarbon discovery.
Publisher
University of Nairobi
Subject
Seismic Stratigraphy AnalysisRights
Attribution-NonCommercial-NoDerivs 3.0 United StatesUsage Rights
http://creativecommons.org/licenses/by-nc-nd/3.0/us/Collections
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